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7 1/2 week embryo, 7.5 week embryo, seven and a half week embryo

Interactive Prenatal Development Timeline

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BODY SYSTEMS SELECTION MENU
Nervous System Cardiovascular Muscular Early Events
Special Senses Respiratory Skeletal General
Blood & Immune Gastrointestinal Endocrine Growth Parameters
Skin Renal/Urinary Reproductive Movement
 




Go to Weeks:
0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12 12-16 16-20 20-24 24-28 28-32 32-36 36-38

Unit 1:   The First Week
     
   
Unit 3:   2 to 3 Weeks
     
  • (2 weeks, 1 day):
  • Early Events3 germ layers
  • Early EventsCloacal membrane
  • Early EventsPrechordal plate
  • Early EventsPrimitive groove
  • Early EventsRostral-caudal orientation
  •  
  • (2 weeks, 2 days): Carnegie Stage 7
  • Blood & ImmuneErythroblasts in yolk sac
  • Blood & ImmuneThree types of blood-forming cells in
  •          yolk sac
  • ReproductivePrimordial germ cells
  • Renal/UrinaryAllantoic diverticulum
  • Early EventsAllantoic diverticulum
  • Early EventsAmnion with two cell layers
  • Early EventsSecondary villi
  • (2 weeks, 3 days):
  • Early EventsNotochordal process
  •  
  • (2 weeks, 4 days): Carnegie Stage 8
  • GastrointestinalForegut, midgut, and hindgut
  • CardiovascularUteroplacental circulation well
  •          established
  • Prechordal plate with 1 retinal field
  • Nervous SystemBrain is first organ to appear
  • Nervous SystemNeural ectoderm
  • Nervous SystemNeural groove and neural folds
  • Nervous SystemNotochordal and neurenteric canals
  • Nervous SystemNotochordal plate
  • Early EventsConnecting stalk
  • Early EventsPrimitive pit (or notochordal pit)
  • (2 weeks, 5 days):
  • Prechordal plate with 2 retinal fields
  •  
  • (2 weeks, 6 days): Carnegie Stage 9
  • Blood & ImmuneNumerous blood islands in umbilical
  •          vesicle
  • MuscularSeptum transversum (primitive diaphragm)
  • GastrointestinalForegut
  • GastrointestinalPharyngeal pouch 1
  • GastrointestinalStomodeum forming
  • CardiovascularBlood vessels emerge simultaneously in
  •          umbilical vesicle, embryo proper, amnion,
  •          and connecting stalk
  • CardiovascularDorsal aortae (paired)
  • CardiovascularFirst pair of aortic arches
  • CardiovascularHeart: Cardiogenic plate, cardiac jelly,
  •          myocardial mantle, and endocardial plexus
  • CardiovascularPaired pericardial cavities
  • CardiovascularPaired tubular heart
  • Nervous SystemCaudal eminence
  • Nervous SystemHindbrain with four rhombomeres
  • Nervous SystemIsthmus rhombencephali demarcates
  •          midbrain and hindbrain
  • Nervous SystemMesencephalon (or midbrain)
  • Nervous SystemNeural groove deepens substantially
  • Nervous SystemPrimary neuromeres
  • Nervous SystemThree main divisions of brain
  • Early EventsCephalic and caudal folds
  • Early EventsNeural crest: Rostral and facial
  • Early EventsPrimitive streak reaches neurenteric
  •          canal
  • Early EventsSomites with central somitocoels: Pairs
  •          1 through 3
   
Unit 5:   4 to 5 Weeks
     
  • (4 weeks, 4 days): Carnegie Stage 14
  • Blood & ImmuneThymus
  • EndocrineParathyrogenic zones
  • EndocrineThyroglossal duct
  • EndocrineThyroid pedical lengthens
  • SkeletalDorsal contour develops depression at
  •          level of sclerotomes 4 and 5
  • MuscularMuscular plates between upper and lower
  •          limb buds
  • Renal/UrinaryGlomerular capsules, partially
  •          vascularized
  • Renal/UrinaryMesonephric corpuscle
  • Renal/UrinaryMetanephrogenic cap emerges from
  •          ureteric bud
  • Renal/UrinaryUreteric buds
  • GastrointestinalAngiogenesis within peri-esophageal
  •          mesenchyme
  • GastrointestinalEpiploic foramen
  • GastrointestinalLesser sac (omental bursa)
  • GastrointestinalSmall intestine forming coils
  • GastrointestinalTongue: Hypopharyngeal eminence
  • RespiratoryArytenoid swellings (right and left)
  • RespiratoryCapillary network surrounds pulmonary
  •          mesenchyme
  • RespiratoryEpithelial lamina of larynx
  • RespiratoryLungs: Right and left primary (or main
  •          stem) bronchi
  • RespiratoryMesenchyme covering esophagus and
  •          respiratory tree separates
  • RespiratoryMesenchyme surrounds bronchi
  • RespiratoryPleura (mesothelium) surrounds part of
  •          mesenchyme
  • RespiratoryRight main bronchus longer than left
  • CardiovascularAtria walls thin, ventricle walls thick
  •          and trabeculated
  • CardiovascularAtrioventricula cushions not fused
  • CardiovascularConotruncal ridges or cushions (remnants
  •          of cardiac jelly)
  • CardiovascularEpicardium
  • CardiovascularOutflow tract still with one lumen
  • CardiovascularPosterior communicating arteries
  • CardiovascularPulmonary arch (sixth aortic arch) forms
  •          from aorta and aortic sac
  • CardiovascularPulmonary capillary network fed by
  •          pulmonary arteries, drain into left
  •          atrium
  • CardiovascularSinu-atrial (SA) node
  • CardiovascularSuperior mesenteric artery and vein
  • CardiovascularUpper limb buds with early marginal
  •          blood vessel
  • Special SensesBrachial plexus
  • Special SensesCervical plexus
  • Special SensesDorsal roots
  • Special SensesHypoglossal nerve roots unite (CN XII)
  • Special SensesLens and retina invaginate to form optic
  •          cup
  • Special SensesPrimordium of cochlear duct
  • Special SensesRami communicantes
  • Special SensesSpinal nerves reach muscle primordia
  • Special SensesUpper limb buds innervated
  • Nervous SystemD1 and D2 no longer identifiable within
  •          diencephalon
  • Nervous System75% of midbrain covered by marginal
  •          layer
  • Nervous SystemAdenohypophysis
  • Nervous SystemAll 16 secondary neuromeres
  • Nervous SystemBrain enlarges 50% since Carnegie Stage
  •          13
  • Nervous SystemBrain: Cerebral hemispheres appear and
  •          begin rapid growth
  • Nervous SystemBrain: Lateral ventricles
  • Nervous SystemCerebellum with intermediate and
  •          ventricular layers
  • Nervous SystemCerebellum: Primordium found in alar
  •          plate of rhombomere 1
  • Nervous SystemCorpora striata primordia connected by
  •          commissural plate
  • Nervous SystemCranial nerve 3
  • Nervous SystemDi-telencephalic sulcus
  • Nervous SystemDorsal and ventral thalami
  • Nervous SystemDorsal funiculus
  • Nervous SystemMamillary region
  • Nervous SystemMedial and lateral longitudinal
  •          fasciculi
  • Nervous SystemMedian ventricular eminence
  • Nervous SystemPontine flexure
  • Nervous SystemPreoptic sulcus extends between optic
  •          evaginations
  • Nervous SystemPreoptico-hypothalamo-tegmental tract
  • Nervous SystemPrimary meninx surrounds most of brain
  • Nervous SystemRhombic lip
  • Nervous SystemSpinal cord wall with three zones:
  •          ventricular (ependymal) zone, mantle
  •          (intermediate) zone, and marginal zone
  • Nervous SystemSubthalamus with medial striatal ridge
  •          emerging
  • Nervous SystemSynencephalon
  • Nervous SystemTegmentum
  • Nervous SystemTentorium cerebelli, medial portion
  • Nervous SystemTerminal-vomeronasal crest contacts
  •          brain (olfactory area)
  • Nervous SystemTorus hemisphericus (TH)
  • Nervous SystemVelum transversum
  • Nervous SystemVentral longitudinal fasciculus
  • Early EventsVentral segment of hyoid arch subdivides
  •  
  • (4 weeks, 5 days): Carnegie Stage 15
  • SkinPrimordium of antitragus emerges from
  •          ventral subsegment of hyoid arch
  • ReproductiveGonad framework found in coelomic
  •          epithelium
  • EndocrineThyroid detached from epithelium of
  •          pharynx in some embryos
  • SkeletalLower limb bud rounded proximally and
  •          tapered distally
  • SkeletalMesenchymal skeleton in upper and lower
  •          limbs
  • SkeletalRight and left neural processes
  • SkeletalSclerotomic material around notochord
  •          (rhombomere D level)
  • SkeletalVertebrae well defined
  • SkeletalVertebral centra
  • Renal/UrinaryPrimary urogenital sinus
  • Renal/UrinaryUreteric bud extends to pelvis of the
  •          ureter
  • GastrointestinalBladder and rectum are separating caudal
  •          to ureters
  • GastrointestinalDense mesenchyme surrounds much of
  •          gastrointestinal tract
  • GastrointestinalEsophagus elongates, passes dorsal to
  •          carina and between main stem bronchi
  • GastrointestinalGall bladder and cystic duct
  • GastrointestinalLiver: Hepatic ducts
  • GastrointestinalVentral pancreas appears as an offshoot
  •          of the cystic duct
  • RespiratoryLobar bud swellings denote areas of
  •          secondary bronchi
  • RespiratoryRemnants of coelomic epithelium forming
  •          visceral pleura
  • CardiovascularAtrioventricular cushions apposed
  • CardiovascularBlood flow divided into right and left
  •          streams through atrioventricular canal,
  •          ventricles, outflow tract, and aortic sac
  • CardiovascularBlood vessels penetrate diencephalon
  • CardiovascularCapillary plexus surrounds esophagus
  • CardiovascularCapillary plexus surrounds lung buds
  • CardiovascularCardiac mesenchyme surrounds ventricles
  •          and outflow tract
  • CardiovascularCommon pulmonary vein drains pulmonary
  •          plexuses into left atrium
  • CardiovascularCoronary arteries (terminal end)
  • CardiovascularForamen secundum begins in septum primum
  • CardiovascularLeft ventricle with thicker walls and
  •          greater volume than right
  • CardiovascularSemilunar cusps
  • Special SensesCapsule present around lens
  • Special SensesCorneal epithelium overlying optic cup
  • Special SensesEar: Endolymphatic duct
  • Special SensesGeniculate and vestibulocochlear ganglia
  •          separating
  • Special SensesLens body now present containing some
  •          lens fibers
  • Special SensesLower limb buds innervated
  • Special SensesOptic stalk
  • Special SensesUtriculo-endolymphatic fold
  • External ear primordia emerges from
  •          caudolateral portion of mandibular arch
  • Face: Lateral and medial nasal processes
  •          bilaterally
  • Lateral nasal processes along
  •          dorsolateral lip of nasal pits
  • Optic chiasm
  • Pigment in retina (external layer of
  •          optic cup)
  • Nervous SystemAdult lamina terminalis
  • Nervous SystemAmygdaloid area
  • Nervous SystemCerebellar plate
  • Nervous SystemCerebellum with marginal layer
  • Nervous SystemFibers of dorsal funiculus reach level
  •          of C1
  • Nervous SystemFirst axodendritic synapses in cervical
  •          spinal cord
  • Nervous SystemFirst nerve fibers
  • Nervous SystemHabenular nucleus
  • Nervous SystemHabenulo-interpeduncular tract
  • Nervous SystemHypothalamic sulcus
  • Nervous SystemHypothalamus
  • Nervous SystemLateral striatal ridge (derived from
  •          telencephalon and comprised mainly of
  •          neostriatum)
  • Nervous SystemLateral ventricular eminence
  • Nervous SystemLocus caeruleus
  • Nervous SystemLongitudinal zones in diencephalon
  • Nervous SystemMarginal layer throughout most of
  •          diencephalon
  • Nervous SystemMaterial for sympathetic trunks
  •          scattered in cervical region
  • Nervous SystemMedian striatal ridge (paleostriatum)
  • Nervous SystemMesencephalic tract of CN 5
  • Nervous SystemMost cranial nerves seen
  • Nervous SystemOlfactory fibers reach brain
  • Nervous SystemOptic groove (also called preoptic
  •          recess)
  • Nervous SystemPostoptic recess
  • Nervous SystemPrimordium of epiphysis
  • Nervous SystemRhombomeres still identifiable
  • Nervous SystemSuperior colliculi and its commissure
  • Nervous SystemSuperior medullary velum
  • Nervous SystemSupramamillary commissure
  • Nervous SystemSynapses among motor neurons in spinal
  •          cord
  • Nervous SystemTectobulbar tract
  • Nervous SystemTentorium
  • Nervous SystemThird ventricle
  • Nervous SystemTrigemino-cerebellar tract
  • Nervous SystemTrochlear nerve root and decussation (CN
  •          IV)
  • Early EventsHand plate emerges from distal upper
  •          limb bud
  • (5 weeks):
  • RespiratoryArytenoid and epiglottal swellings
  • RespiratoryLobar pattern mimics adult pattern
  • RespiratoryT-shaped laryngeal inlet
  • CardiovascularPacemaker cells
   
Unit 7:   6 to 7 Weeks
     
  • (6 weeks, 2 days): Carnegie Stage 18
  • ReproductiveAngiogenesis begins inside gonads
  • ReproductiveGonad grows into oval shape with
  •          irregular surface
  • ReproductiveOstium (abdominal) of uterine tube at
  •          rostral end of paramesonephric duct (in
  •          female embryos)
  • ReproductiveParamesonephric duct forms from rostral
  •          end of mesonephric duct
  • ReproductiveTesticular cords in gonads of male
  •          embryos
  • ReproductiveTesticular cords in male gonad
  • SkeletalElbow regions sometimes identifiable
  • SkeletalEmbryo with cervical and lumbar flexures
  • SkeletalEmbryo with dorsal concavity
  • SkeletalFinger rays with early interdigital
  •          notching
  • SkeletalHumerus: Chondrocytes in phases one
  •          through three
  • SkeletalPrimordium of cartilage within nasal
  •          septum
  • SkeletalSemicircular ducts form in order:
  •          anterior, posterior, and lateral
  • SkeletalToe rays sometimes present
  • MuscularStapedius muscle
  • Renal/Urinary"Common excretory duct is disappearing"
  • Renal/UrinaryCloacal membrane ruptures (stages 18-19)
  • Renal/UrinaryPrimordia of secretory tubules
  • GastrointestinalEsophagus with muscular and submucous
  •          coats
  • GastrointestinalSubmandibular gland primordia
  • RespiratoryBronchial tree with subsegmental buds
  • RespiratoryBronchial tree with well established
  •          segmental bronchi
  • CardiovascularAortic and pulmonary valves assuming
  •          shape of a cup
  • CardiovascularInferior vena cava
  • CardiovascularInterventricular septum: membranous part
  •          begins forming
  • CardiovascularMesenchyme ridges in place of future
  •          mitral and tricuspid valves
  • CardiovascularOrigin of left coronary artery
  • CardiovascularPulmonary and aortic blood flows
  •          completely separate
  • CardiovascularSecondary interventricular foramen
  •          sometimes closing (stage 18-21)
  •          interventricular septum
  • CardiovascularSeptum secundum and foramen ovale
  •          (stages 18-21)
  • CardiovascularSuperior vena cava, inferior vena cava,
  •          and sinus venosus collecting all venous
  •          blood
  • Special SensesBucconasal membrane
  • Special SensesBucconasal membrane detaches opening up
  •          nasal airway
  • Special SensesCrus commune
  • Special SensesEthmoidal epithelium emerges from upper
  •          medial nasal wall
  • Special SensesFrontonasal angle (marks location of
  •          future nasal bridge)
  • Special SensesMesenchyme thickenings mark beginning of
  •          "sclera and its muscular attachments"
  • Special SensesNasal tip emerges
  • Special SensesNerve fibers in retina
  • Special SensesOptic fibers
  • Special SensesRetina's outer lamina heavily pigmented
  • Special SensesVomeronasal nerve and ganglion
  • Special SensesVomeronasal organ marked by groove and
  •          located in fold of lower medial nasal
  •          wall
  • Ear: Stapes primordium surrounds
  •          stapedial artery
  • External ear: Crus helicis forming from
  •          auricular hillocks two and three (from
  •          mandibular arch)
  • Eyelid folds sometimes present
  • Nasolacrimal duct begins as epithelial
  •          strand emanating from nasomaxillary
  •          groove
  • Nostrils, nasal wings, and nasal septum
  •          easily seen
  • Olfactory bulb sometimes with olfactory
  •          ventricle
  • Nervous SystemAdenohypophysis no longer open to
  •          pharyngeal cavity
  • Nervous SystemArchistriatum
  • Nervous SystemBrain: Dentate nucleus in internal
  •          cerebellar swellings
  • Nervous SystemBrain: Pineal recess emerges
  •          representing anterior lobe of epiphysis
  • Nervous SystemCerebrospinal fluid production begins
  • Nervous SystemChoroid plexuses in fourth and lateral
  •          ventricles
  • Nervous SystemCorpus striatum much larger extending to
  •          preoptic sulcus; has subtle groove
  • Nervous SystemExternal cerebellar swellings contain
  •          future flocculus
  • Nervous SystemFour amygdaloid nuclei
  • Nervous SystemFourth ventricle: Choroid folds
  • Nervous SystemHippocampus reaches olfactory region
  • Nervous SystemNeurohypophysis walls are folded
  • Nervous SystemNucleus ambiguus of the vagus (CN10)
  • Nervous SystemProsencephalic septum
  • Nervous SystemRed nucleus
  • Nervous SystemSubstantia nigra
  • Nervous SystemSupraoptic commissure
  • (6½ weeks):
  • SkinVolar pads on palms
  •  
  • (6 weeks, 5 days): Carnegie Stage 19
  • Blood & ImmuneGreater thymic bud
  • SkinCheeks form by merging of maxillary and
  •          mandibular processes
  • SkinMammary gland primordium
  • SkinMammary ridge disappears leaving only
  •          mammary gland primordium
  • ReproductiveFemale duct
  • ReproductiveGonads extend from levels T-10 to L-2
  • ReproductiveRete ovarii (in female embryos)
  • ReproductiveRete testis begins emerging from
  •          seminiferous cords (Stage 19-23) (in male
  •          embryos)
  • ReproductiveTunica albuginea in male embryos
  • EndocrineSuprarenal gland: Cortex
  • EndocrineSuprarenal gland: Medulla populated by
  •          prechromaffin cells
  • SkeletalBeginnings of occipital and sphenoid
  •          bones
  • SkeletalBilateral cartilaginous sternal bars tie
  •          ribs together; sternal bars join
  •          cranially to form the episternal bar in
  •          the midline
  • SkeletalCartilage within otic capsule envelops
  •          semicircular canals and cochlear duct
  • SkeletalCartilaginous styloid process
  • SkeletalEar: Cartilaginous malleus, incus, and
  •          stapes (the middle ear ossicles)
  • SkeletalEctomeninx covers lateral and dorsal
  •          surfaces of brain (laying the foundation
  •          for the flat bones of the skull)
  • SkeletalHumerus, radius, and ulna
  • SkeletalIntervertebral discs form from caudal
  •          condensed portion of sclerotomes
  • SkeletalIschium and illium
  • SkeletalLabiodental lamina: Inner dental lamina
  •          and outer labiogingival band
  • SkeletalLaryngeal cartilages
  • SkeletalOrbitosphenoid cartilage located within
  •          ectomeninx near optic stalk
  • SkeletalOssification begins in maxilla (stages
  •          19 -20)
  • SkeletalPrimitive palate (or intermaxillary
  •          segment)
  • SkeletalRib primordia become cartilaginous
  • SkeletalRibs each have an identifiable head and
  •          shaft
  • SkeletalScapula and clavicle
  • SkeletalSternum: Episternal cartilage created
  •          from fusion of right and left sternal
  •          bars
  • SkeletalTibia and fibula
  • SkeletalTrachea: Tracheal cartilage
  • SkeletalU-shaped labiodental lamina form along
  •          upper and lower oral cavity
  • SkeletalVertebral column represented by
  •          cartilaginous centrum, neural arch, and
  •          short tranverse process
  • MuscularDeltoid muscle
  • MuscularEsophagus: Muscularis layer adjacent to
  •          esophageal plexus
  • MuscularExternal and internal abdominal oblique
  •          muscles
  • MuscularGluteal muscle group
  • MuscularIliopsoas muscles
  • MuscularInfrahyoid muscles
  • MuscularInternal intercostal muscles
  • MuscularLevator scapulae muscle
  • MuscularLimb extensor muscles located dorsally
  • MuscularLimb flexor muscles located ventrally
  • MuscularLongus cervicis and semispinalis
  •          cervicis muscles
  • MuscularMidgut: Muscularis
  • MuscularMuscle tissue forming around phrenic
  •          nerve within septum transversum portion
  •          of diaphragm
  • MuscularPectoralis major muscles
  • MuscularPharyngeal constrictor muscle
  • MuscularPlatysma muscle
  • MuscularPremuscle mass of the muscles of
  •          mastication innervated by mandibular
  •          nerve
  • MuscularQuadratus lumborum muscle
  • MuscularRectus abdominis muscle
  • MuscularRectus capitus posterior and
  •          semispinalis capitis muscles
  • MuscularRhomboid and scalene muscles
  • MuscularSerratus anterior muscles
  • MuscularSplenius and longissimus muscles
  • MuscularSternocleidomastoid and trapezius
  •          muscles distinct and innervated by
  •          separate branches of spinal accessory
  •          nerve (CN XI)
  • MuscularThenar and hypothenar eminences
  • MuscularTongue forms from swellings in floor of
  •          pharynx
  • MuscularTongue: Extrinsic muscles identifiable
  • MuscularTongue: Intrinsic muscles identifiable
  • MuscularTransversospinal and erector spinae
  •          muscle groups
  • MuscularUpper limb flexors innervated by
  •          musculocutaneous, median, and ulnar
  •          nerves
  • Renal/UrinaryMajor calyces, cranial and caudal, with
  •          collecting tubules within metanephrogenic
  •          mass
  • Renal/UrinaryMesonephros extends from T-9 to L-3
  • Renal/UrinaryMetanephros extends from T-12 to L-2
  • Renal/UrinaryRenal capsule covers distal collecting
  •          tubules
  • Renal/UrinaryRenal vesicles form in part of
  •          metanephros
  • Renal/UrinaryUreter forms from "proximal segment of
  •          metanephric diverticulum"
  • Renal/UrinaryUrogenital sinus comprised of three
  •          parts: Bladder, pelvic, and phallic
  •          portions
  • GastrointestinalAnal folds adjacent to anal membrane
  • GastrointestinalAnal membrane
  • GastrointestinalCommon coelomic cavity divides into
  •          peritoneal, pericardial, and pleural
  •          cavities
  • GastrointestinalDuodenum: "Assumes the shape of an arc"
  • GastrointestinalGreater omentum
  • GastrointestinalLateral palatine process
  • GastrointestinalLiver: rapid growth, right side greater
  •          than left
  • GastrointestinalMedian mandibular groove disappears as
  •          mandibular processes merge in midline
  • GastrointestinalPalatine fossa (from pharyngeal pouch 2)
  • GastrointestinalPrimitive oral cavity
  • GastrointestinalPrimitive rima oris replaces stomodeum
  • GastrointestinalStomach wall layers: Mucosa, submucosa,
  •          muscularis, and serosa
  • GastrointestinalSubmandibular and parotid gland buds
  • GastrointestinalSubmandibular gland duct
  • RespiratoryBronchial tree: First generation of
  •          subsegmental bronchi complete
  • RespiratoryGlottis, primitive
  • RespiratoryLung sac, right: Oblique and horizontal
  •          fissures define upper, lower, and middle
  •          lobes
  • RespiratoryLung sac: Apex and base
  • RespiratoryLung, left: Oblique fissure defines
  •          upper and lower lobes
  • Cardiovascular"Septum primum fuses with endocardial
  •          cushions" obliterating ostium primum and
  •          creating the ostium secundum
  • CardiovascularApex of left ventricle
  • CardiovascularBrachiocephalic veins, right and left
  • CardiovascularCirculus arteriosus (Circle of Willis)
  •          complete
  • CardiovascularExternal iliac arteries
  • CardiovascularIliac lymph sac
  • CardiovascularIntercostal and subcostal arteries
  • CardiovascularInternal thoracic artery and
  •          costocervical trunk
  • CardiovascularLeft subclavian artery feeds left
  •          axillary and vertebral arteries and left
  •          thyrocervical trunk
  • CardiovascularMesenteric lymph sac
  • CardiovascularMesonephric artery feeds mesonephros,
  •          gonads, and suprarenal glands
  • CardiovascularOrigin of right coronary artery
  • CardiovascularPaired common iliac veins feed inferior
  •          vena cava
  • CardiovascularPapillary muscles
  • CardiovascularPontine, superior cerebellar, and
  •          anterior and posterior interior
  •          cerebellar arteries replace
  •          myelencephalic and metencephalic arteries
  • CardiovascularPrimitive cavernous sinus drains
  •          primitive maxillary and supraorbital
  •          veins
  • CardiovascularPrimitive marginal sinus drains
  •          diencephalon
  • CardiovascularPrimitive tentorial sinus drains
  •          cerebral vesical
  • CardiovascularPrimitive transverse and sigmoid sinuses
  • CardiovascularPulmonary arteries (right and left)
  • CardiovascularRight subclavian artery originates from
  •          brachiocephalic artery and feeds right
  •          thyrocervical trunk and axillary and
  •          vertebral arteries
  • CardiovascularSplenic vein
  • CardiovascularTricuspid and mitral valves
  • Special SensesAnterior chamber between iridopupillary
  •          membrane and thickened ectoderm
  • Special SensesAuditory tube and primtive tympanic
  •          cavity form from tubotympanic recess
  •          pharyngeal pouch 1)
  • Special SensesCeliac, superior mesenteric, and
  •          inferior mesenteric preaortic ganglia
  • Special SensesChoana
  • Special SensesCochlear duct tip grows upward
  • Special SensesEsophageal plexus formed by vagal nerves
  •          (CN X)
  • Special SensesFacial nerve (CN VII) branches: Chorda
  •          tympani, greater petrosal, posterior
  •          auricular, and digastric
  • Special SensesFacial nerve (CN VII) reaches
  •          cervicomandibular region
  • Special SensesGlossopharyngeal nerve (CN IX)
  •          innervates stylopharyngeus premuscle mass
  • Special SensesHypoglossal nerve (CN XII) innervates
  •          separating tongue muscles
  • Special SensesLinguogingival groove
  • Special SensesNasolacrimal duct forms from
  •          maxillonasal groove
  • Special SensesNasolacrimal ducts extend from medial
  •          eyes to primitive nasal cavity
  • Special SensesNerve fibers begin extending from retina
  • Special SensesOptic fibers enter chiasmatic plate
  • Special SensesPrimitive nasal cavity
  • Special SensesPrimordial vitreous body
  • Special SensesSuperior, middle, and inferior cervical
  •          ganglia
  • Special SensesTrigeminal nerve (CN V) with opthalmic,
  •          maxillary, and mandibular divisions reach
  •          their destinations
  • Special SensesUtricle, endolymphatic duct, and
  •          endolymphatic sac
  • Special SensesVagal trunks, anterior and posterior,
  •          extending into abdomen
  • Eyelids: Upper and lower lids present
  •          and growing
  • Nervous SystemAdenohypophysis: Lateral lobes of pars
  •          tuberalis
  • Nervous SystemAdenohypophysis: Pars intermedia
  •          emerging
  • Nervous SystemBrain: Internal capsule formation
  •          underway
  • Nervous SystemCerebral hemispheres cover half of
  •          diencephalon
  • Nervous SystemDorsal and ventral cochlear nuclei
  • Nervous SystemFourth ventricle: Lateral recesses
  • Nervous SystemGanglion of nervus terminalis
  • Nervous SystemGlobus pallidus externus in the
  •          diencephalon
  • Nervous SystemHabenular commissure
  • Nervous SystemHippocampus: Gyrus dentatus
  • Nervous SystemIntermediate layer in dorsal thalamus
  • Nervous SystemInterpeduncular fossa
  • Nervous SystemLemniscal decussation
  • Nervous SystemLower limb nerves (femoral, obturator,
  •          sciatic, common peroneal, and tibial)
  •          identifiable
  • Nervous SystemMedial accessory olivary nucleus
  • Nervous SystemNeurohypophyseal bud
  • Nervous SystemNuclei of forebrain septum
  • Nervous SystemNucleus accumbens
  • Nervous SystemOccipital pole of cerebral hemispheres
  • Nervous SystemOptic stalk with barely discernible
  •          lumen
  • Nervous SystemParaphysis marks dividing line in roof
  •          between telencephalon and diencephalon
  • Nervous SystemPrimitive filum terminale
  • Nervous SystemRadial nerve innervates upper limb
  •          extensors
  • Nervous SystemRhombomeres no longer distinguishable
  • Nervous SystemSubcommissural organ
  • Nervous SystemZona limitans intrathalamica between
  •          dorsal and ventral thalami
  • (6 weeks, 6 days):
  • GastrointestinalCloacal membrane ruptures
  • (7 weeks):
  • MovementHead rotates
  • ReproductiveOvaries
  • CardiovascularThe heart has four chambers and is
  •          nearly complete.
  • CardiovascularThe heart rate peaks at 165 to 170 beats
  •          per minute.
  • GeneralCrown-heel length 2.2 cm
   
Unit 9:   8 to 9 Weeks
     
   
Unit 11:   10 to 11 Weeks
     
   
Unit 13:   3 to 4 Months
     
  • (13 weeks):
  • SkeletalTeeth are growing
  • GeneralCrown-heel length 15 cm
  •  
  • (14 weeks):
  • MovementGirls move their jaws more than the boys
  •          do
  • Nervous SystemCerebellum resembles adult structure
  • GeneralCrown-heel length 17 cm
  •  
  • (15 weeks):
  • GeneralCrown-heel length 19.5 cm
  •  
  • (16 weeks):
  • MovementQuickening
  • GastrointestinalColon lined with villi
  • RespiratoryCanalicular stage begins
  • GeneralCrown-heel length 21 cm
   
Unit 15:   5 to 6 Months
     
  • (21 weeks):
  • SkinPeriderm disappears
  • SkinStratum corneum
  •  
  • (22 weeks):
  • Nervous SystemBehavioral states
  •  
  • (23 weeks):
  • GeneralBrain weight 100 grams
  •  
  • (24 weeks):
  • GeneralCrown-heel length 34.5 cm
   
Unit 17:   7 to 8 Months
     
   
Unit 19:   9 Months to Birth
     
  • (37 weeks):
  • GastrointestinalFetus drinks an estimated 15 oz (or
  •          450cc) of amniotic fluid/day
  •  
  • (38 weeks):
  • CardiovascularHeart beats 54 million times before
  •          birth
  • Nervous SystemSpinal cord ends at third lumbar
  •          vertebrae
  • GeneralBrain weight 350 grams
  • GeneralCrown-heel length 50 cm
  • GeneralHead circumference 35 cm
  • GeneralTime to be born!
   
Fertilization
Play Movie - Cell Division
Week 1 ends
Play Movie - 1 to 2 weeks, implantation and HCG
Week 2 ends
Play Movie - 2 to 3 week embryo, amnion, germ layer
Week 3 ends
Play Movie - 3 to 4 week embryo, folding of the embryo
Week 4 ends
Play Movie - 4 to 5 week embryo, The Heart in Action
Week 5 ends
Play Movie - 5 to 6 week embryo, hand plates develop
Week 6 ends
Play Movie - 6 to 7 week embryo, hand movement
Week 7 ends
Play Movie - 7 to 8 week embryo, fingers, toes
Week 8 ends
Play Movie - 8 to 9 week fetus, reflexive movement
Week 9 ends
Play Movie - 9 to 10 week fetus, sucking, swallowing
Week 10 ends
Play Movie - 10 to 11 week fetus, eyes roll, yawns
Week 11 ends
Play Movie - 11 to 12 week fetus, nails, fingerprints
Month 3 ends
Play Movie - 3 to 4 month fetus, the rooting reflex
Month 4 ends
Play Movie - 4 to 5 month fetus, bronchial tree
Month 5 ends
Play Movie - 5 to 6 months fetus, responds to sound
Month 6 ends
Play Movie - 6 to 7 month fetus, response to light
Month 7 ends
Play Movie - 7 to 8 month fetus, behavioral states
Month 8 ends
Play Movie - 8 to 9 month fetus, firm hand grasp
Month 9 ends
Play Movie - 9 months to Birth, ready for Birth
Birth
1124 events on this timeline
Click any picture to see more!
Unit 2:   1 to 2 Weeks
     
  • (1 week, 1 day):
  • EndocrinePositive pregnancy test
  • Early EventsAmnioblasts present; amnion and amniotic
  •          cavity formation begins
  • Early EventsBilaminar embryonic disc
  •  
  • (1 week, 2 days): Carnegie Stage 5b
  • EndocrineCorpus luteum of pregnancy
  • Early EventsCells in womb engorged with nutrients
  • Early EventsExocoelomic membrane
  • Early EventsIsolated trophoblastic lacunae
  • GeneralEmbryonic disc 0.1 mm diameter
  •  
  • (1 week, 4 days): Carnegie Stage 5c
  • Early EventsIntercommunicating lacunae network
  • Early EventsLongitudinal axis
  • Early EventsTrophoblastic vascular circle
  • (1 week, 5 days):
  • Early EventsImplantation complete
  • GeneralEmbryonic disc diameter: 0.15 to 0.20 mm
  •  
  • (1 week, 6 days): Carnegie Stage 6
  • Blood & ImmuneBlood islands in umbilical vesicle
  • Renal/UrinaryAllantois
  • CardiovascularAngiogenesis in chorionic mesoblast
  • CardiovascularBlood vessels in villi
  • CardiovascularConnecting stalk
  • CardiovascularPrimordial blood vessels
  • Early EventsAmnion with single cell layer
  • Early EventsChorionic villi
  • (2 weeks):
  • Early EventsEmbryonic epiblast gives rise to
  •          primitive streak and primitive node and
  • Early EventsYolk sac
  • Early EventsYolk sac
   
Unit 4:   3 to 4 Weeks
     
  • (3 weeks, 1 day): Carnegie Stage 10
  • EndocrineThyroid primordium emerges from floor of
  •          pharynx
  • GastrointestinalCloaca
  • GastrointestinalLiver: Hepatic plate (endoderm)
  • GastrointestinalMidgut emerging
  • GastrointestinalOropharyngeal membrane
  • GastrointestinalPharyngeal arches 1 and 2
  • GastrointestinalPharyngeal cleft 1
  • GastrointestinalSecond pharyngeal cleft and pouch
  • RespiratoryPharyngeal groove and ridge with
  •          laryngotracheal sulcus
  • RespiratoryRespiratory outgrowth
  • CardiovascularAtria (right and left) far apart
  • CardiovascularBulbis cordis
  • CardiovascularCommon umbilical artery
  • CardiovascularEndocardial tubes fuse forming tubular
  •          heart
  • CardiovascularHeart begins beating
  • CardiovascularLeft ventricle, right ventricle,
  •          conotruncus
  • CardiovascularPericardium
  • CardiovascularPrimary head vein
  • CardiovascularSinus venosus
  • CardiovascularTubular heart begins folding
  • CardiovascularUmbilical arteries
  • CardiovascularUmbilical veins (right and left)
  • Special SensesOptic primordia fill neuromere D2
  • Special SensesOtic plates
  • Nervous SystemChiasmatic plate
  • Nervous SystemMesencephalic flexure
  • Nervous SystemNeural tube
  • Nervous SystemNeuromeres D1 and D2 (in diencephalon)
  • Nervous SystemOptic sulcus in forebrain
  • Nervous SystemPontine region identifiable near cranial
  •          nerves VII and VIII
  • Nervous SystemSegment D in rhombencephalon
  • Nervous SystemSome secondary neuromeres
  • Nervous SystemTelencephalon
  • Nervous SystemTelencephalon (or telencephalic) medium
  • Early EventsBody cavities
  • Early EventsHyoid arch
  • Early EventsMandibular arch and maxillary process
  • Early EventsNeural crest: Trigeminal, facioacoustic,
  •          glossopharyngeal-vagal, and
  •          occipitospinal
  • Early EventsSomites: Pairs 4 through 12
  • (3 weeks, 2 days):
  • Renal/UrinaryNephrogenic cord emerges (at 10 somites)
  •  
  • (3 weeks, 3 days): Carnegie Stage 11
  • ReproductivePrimordial germ cells begin moving from
  •          umbilical vesicle to hindgut
  • SkeletalFace: Maxillary and mandibular processes
  •          (bilaterally)
  • Renal/UrinaryCloacal membrane
  • Renal/UrinaryMesonephric duct emerges from
  •          nephrogenic cord
  • Renal/UrinaryNephric vesicles
  • GastrointestinalCystic primordium
  • GastrointestinalHepatic diverticulum
  • GastrointestinalLiver
  • GastrointestinalMembrane between future mouth and throat
  •          may begin to rupture
  • CardiovascularAngiogenesis along surface of central
  •          nervous system
  • CardiovascularAortic sac
  • CardiovascularAtrioventricular canal
  • CardiovascularCapillary plexus begins forming around
  •          brain and spinal cord
  • CardiovascularConotruncus
  • CardiovascularConus cordis emerging from right
  •          ventricle
  • CardiovascularEndocardium
  • CardiovascularHeart contractions produce peristaltic
  •          blood flow
  • CardiovascularInterventricular septum
  • CardiovascularPrimordium of myocardium
  • CardiovascularSinus venosus separating from left atria
  • CardiovascularTrabeculated outpouches along primary
  •          cardiac tube representing primordia of
  •          left and right ventricles
  • CardiovascularTrigeminal and otic arteries
  • Special SensesFacio-vestibulocochlear ganglia (CN VII,
  •          CN VIII)
  • Special SensesGlossopharyngeal and vagal ganglia
  • Special SensesOptic evagination (starting at 14
  •          somites)
  • Special SensesOtic vesicle
  • Special SensesTrigeminal ganglia (CN V)
  • Nervous SystemLamina terminalis
  • Nervous SystemMesencephalon contains tectum and
  •          tegmentum
  • Nervous SystemNeural crest production and migration
  •          continue
  • Nervous SystemNeurohypophysial primordia
  • Nervous SystemNeuropore (near brain) closes
  • Nervous SystemNotochord
  • Early EventsSegmentation of mesoblast alongside
  •          neural tube bilaterally
  • Early EventsSomites: Pairs 13 through 20
  • (3 weeks, 3 days - 5 weeks, 6 days):
  • Nervous SystemAll eight rhombomeres (Rh 1 through Rh
  •          7, Rh D) - Present in stages 11 through
  •          17
  •  
  • (3 weeks, 5 days): Carnegie Stage 12
  • EndocrineTelopharyngeal bodies
  • GastrointestinalAlimentary epithelium invades stroma of
  •          liver
  • GastrointestinalAlimentary epthelium proliferates in
  •          primordia of stomach, liver, and dorsal
  •          pancreas
  • GastrointestinalFirst part of pancreas
  • GastrointestinalGastric portion of foregut elongates (25
  •          to 28 somites)
  • GastrointestinalHepatic primordium with abundant
  •          vascular plexus
  • GastrointestinalOmental bursa
  • GastrointestinalOropharyngeal membrane is ruptured
  • GastrointestinalPharyngeal arch 3
  • GastrointestinalPharyngeal arches with dorsal and
  •          ventral parts
  • GastrointestinalUmbilical vesicle elongates
  • RespiratoryCervical sinus
  • RespiratoryLaryngotracheal groove
  • RespiratoryLung bud
  • RespiratoryTracheo-esophageal septum
  • CardiovascularAtrioventricular canal
  • CardiovascularCommon cardinal veins (right and left)
  • CardiovascularDescending aorta
  • CardiovascularHeart circulates blood to and from
  •          central nervous system, umbilical
  •          vesicle, and chorion
  • CardiovascularHepatocardiac channels (right and left)
  • CardiovascularInternal carotid arteries
  • CardiovascularRostral and caudal cardinal veins along
  •          brain and spinal cord feeding common
  •          cardinal veins
  • CardiovascularSeptum primum and foramen primum
  •          sometimes present
  • CardiovascularSinu-atrial foramen prevents backflow
  •          into sinus venosus
  • CardiovascularSinus venosus collects veinous blood
  •          from entire embryo
  • CardiovascularUnidirectional circulation
  • CardiovascularVitelline arteries and veins
  • Special SensesHypoglossal cord (CN XII) enters
  •          pharyngeal arch 4
  • Special SensesOtocyst nearly closed
  • Nasal discs form part of ectodermal ring
  • Nervous SystemBrain involves 40% of neural tube
  • Nervous SystemBrain: Embryonic commissural plate
  • Nervous SystemEctodermal ring complete
  • Nervous SystemHypoglossal nucleus (CN XII)
  • Nervous SystemLowermost spinal cord formation begins
  • Nervous SystemMamillary recess
  • Nervous SystemMarginal layer in rhombencephalon
  • Nervous SystemMesencephalic flexure at 90 degrees
  • Nervous SystemMesencephalon with two neuromeres: M1
  •          and M2
  • Nervous SystemMotor neurons in basal plate of
  •          rhombencephalon
  • Nervous SystemNeural cord within caudal eminence
  • Nervous SystemNeural tube closes (lower back)
  • Nervous SystemNeurofibrils form in rhombencephalon
  • Nervous SystemPrimary neurulation ends
  • Nervous SystemPrimordia of ventral thalamus and
  •          subthalamus in diencephalon
  • Nervous SystemSulcus limitans
  • Nervous SystemSulcus limitans in midbrain
  • Early EventsSomites: Pairs 21 through 29
  • Early EventsUpper limb primordium at level of
  •          somites 8 to 10
  • GeneralProgressively C-shaped embryo
  •  
  • (4 weeks): Carnegie Stage 13
  • Blood & ImmuneSpleen primordia
  • Blood & ImmuneThymic primordia
  • SkinLower lip forms from merging of
  •          mandibular processes
  • SkinMelanoblasts in epidermis
  • ReproductiveGonadal ridge extends from C-7 to T-8
  •          levels
  • ReproductivePrimordial germ cells migrate to
  •          mesonephric ridges
  • ReproductivePrimordial germ cells number several
  •          hundred
  • EndocrineThyroid bilobed and attached to pharynx
  •          by thryoglossal duct
  • MuscularDiaphragm primordia
  • Renal/UrinaryGlomeruli emerge in mesonephros
  • Renal/UrinaryMesonephric duct attached to cloaca
  • Renal/UrinaryNephric tubules now S-shaped
  • Renal/UrinaryUrogenital sinus
  • Renal/UrinaryUrorectal cleavage line
  • GastrointestinalDiverticulum ilei marks division between
  •          foregut and hindgut
  • GastrointestinalIntestines growing in length
  • GastrointestinalOpening between gut and umbilical
  •          vesicle decreases
  • GastrointestinalPancreas: Ventral pancreas
  • GastrointestinalPharyngeal pouches 1 through 4
  • GastrointestinalPharynx
  • GastrointestinalPleuroperitoneal canals
  • GastrointestinalStalk of umbilical vesicle lengthens and
  •          narrows
  • GastrointestinalStomach assumes shape of a spindle
  • GastrointestinalUmbilical vesicle at height of
  •          development
  • GastrointestinalVitelline duct
  • RespiratoryBronchial buds
  • RespiratoryMesenchyme from coelomic epithelium
  •          surrounds esophagus and lung buds
  • RespiratoryTrachea
  • CardiovascularAnterior, middle, and posterior cerebral
  •          plexuses
  • CardiovascularAorta branches include dorsal
  •          intersegmental, lateral segmental, and
  •          ventral segmental arteries
  • CardiovascularAortic arches 4 and 6
  • CardiovascularArtery from the common iliac artery
  •          feeds each lower limb bud
  • CardiovascularAtrioventricular bundle
  • CardiovascularCardiac contractions still under
  •          myogenic control
  • CardiovascularCeliac artery, superior and inferior
  •          mesenteric arteries
  • CardiovascularCirculatory system "well established"
  • CardiovascularCommon iliac arteries (right and left,
  •          from dorsal aorta bifurcation)
  • CardiovascularContractions well coordinated and
  •          sequential from sinus venosus to atria to
  •          ventricles
  • CardiovascularDuctus venosus
  • CardiovascularFunctioning two-chamber heart
  • CardiovascularGas exchange through placenta begins
  • CardiovascularGelatinous reticulum (or cardiac
  •          mesenchyme)
  • CardiovascularHeart chambers bulging with fluid
  • CardiovascularHeart now functions as two parallel
  •          pumps
  • CardiovascularHeart: Atrioventricular cushions
  •          (rostroventral and caudodorsal)
  • CardiovascularHeart: Myocardium wall 3 to 4 cells
  •          thick
  • CardiovascularLiver: Hepatocardiac vein
  • CardiovascularPrimary head veins (right and left)
  •          drain anterior, middle, and posterior
  •          cerebral plexuses and feed precardinal
  •          veins
  • CardiovascularSeptum primum, foramen primum
  • CardiovascularSmall arteries emerging throughout
  •          mesoderm
  • CardiovascularVentricle walls trabeculated
  • CardiovascularVertebral arteries
  • CardiovascularVitelline veins empty exclusively into
  •          hepatic plexus
  • Special SensesMost cranial nerve ganglia
  • Special SensesTrigeminal, glossopharyngeal, and vagal
  •          preganglia
  • Otic invagination
  • Nervous SystemAdenohypophysial pouch
  • Nervous SystemBrain: Commissural plate
  • Nervous SystemCerebellum
  • Nervous SystemCommon afferent tract
  • Nervous SystemFourth ventricle
  • Nervous SystemInterstitial nucleus (part of medial
  •          longitudinal fasciculus)
  • Nervous SystemIsthmus rhombencephali (a new neuromere)
  • Nervous SystemOculomotor (CN III) and trochlear nuclei
  •          (CN IV) in mesencephalon (midbrain) and
  •          isthmus respectively
  • Nervous SystemRetinal and lens discs
  • Nervous SystemTerminal-vomeronasal neural crest
  • Early EventsAmnion surrounds connecting stalk and
  •          vitelline stalk
  • Early EventsHyoid arch sudivides into dorsal and
  •          ventral segments
  • Early EventsLimb buds - the first sign of arms and
  •          legs
  • Early EventsLower limb buds
  • Early EventsUmbilical cord emerging
  • Early EventsUpper and lower limb buds
   
Unit 6:   5 to 6 Weeks
     
  • (5 weeks, 2 days): Carnegie Stage 16
  • SkinApical epidermal ridges
  • SkinMammary ridge
  • SkinMaxillary and premaxillary fields still
  •          widely separated
  • SkinNipples emerge from mammary crest
  • ReproductiveGonad region separates from mesonephros
  • ReproductiveGonadal primordium
  • ReproductiveLabioscrotal swelling
  • ReproductiveUrogenital fold and groove
  • ReproductiveUrorectal septum
  • EndocrineSuprarenal gland: Cortex primordium
  • EndocrineSuprarenal gland: Medulla
  • EndocrineThyroid detaches from pharynx
  • EndocrineThyroid with right and left lobes
  •          connected by an isthmus
  • SkeletalCartilage in mandibular arch
  • SkeletalHand area with central carpal region and
  •          digital plate with marginal vein
  • SkeletalPre-chondrocranium: Otic capsule, nasal
  •          capsule, and parachordal condensations
  • SkeletalPrimordia of primary palate
  • SkeletalRibs: Primordia now present for all 12
  •          pairs
  • SkeletalVertebral column with 36 levels of
  •          ganglia and myotomes
  • MuscularExtraocular premuscle masses receive
  •          cranial nerve fibers [oculomotor (CN
  •          III), trochlear (CN IV), and abducens (CN
  •          VI) nerves]
  • MuscularGluteal mesoderm
  • MuscularInfrahyoid premuscle masses
  • MuscularLimb mesoderm
  • MuscularSternocleidomastoid-trapezius premuscle
  •          mass with spinal accessory nerve (CN11)
  • MuscularThigh and thigh mesoderm
  • MuscularTongue premuscle mass
  • Renal/UrinaryMetanephros at level of sacrum
  • Renal/UrinaryUrethral plate
  • GastrointestinalLesser omentum (ventral mesogastrun)
  • GastrointestinalMesentery from end of duodenum to
  •          proximal half of colon
  • GastrointestinalPeritoneal cavity
  • GastrointestinalRectum
  • GastrointestinalStomach: Greater and lesser curvatures
  • GastrointestinalYolk stalk disappears
  • RespiratoryBronchial tree expanding
  • RespiratoryCervical sinus diminished in size
  • RespiratoryEpiglottis
  • RespiratoryPrimitive Larynx
  • CardiovascularAnterior, middle, and posterior cerebral
  •          arteries
  • CardiovascularAtrioventricular (AV) node
  • CardiovascularAtrioventricular cushions fuse with
  •          interventricular septum
  • CardiovascularCircle of Willis almost complete
  • CardiovascularConotruncal septum
  • CardiovascularEndocardial cushions (rostroventral and
  •          caudodorsal) begin fusing around
  •          atrioventricular canal forming right and
  •          left atrioventricular canals and two
  •          separate blood streams
  • CardiovascularExternal carotid artery
  • CardiovascularForamen primum disappearing
  • CardiovascularHepatic portal vein
  • CardiovascularInfundibulum of right ventricle
  • CardiovascularJugular lymph sac
  • CardiovascularLateral atrioventricular cushions
  • CardiovascularMesencephalic artery
  • CardiovascularMyelencephalic artery
  • CardiovascularPerilental blood vessels
  • CardiovascularPrimitive renal plexus
  • CardiovascularRight ventricle feeds sixth (pulmonary)
  •          aortic arches; left ventricle feeds
  •          fourth aortic arches
  • CardiovascularSemilunar valves (aortic and pulmonary)
  •          are forming
  • CardiovascularVentricles each with three parts: inlet,
  •          trabecular pouch, and outflow tract
  • CardiovascularVentricles enlarge and deepen
  •          side-by-side forming an ever growing
  •          interventricular septum
  • Special SensesCeliac plexus
  • Special SensesCochlear nerve present
  • Special SensesFemoral and obturator nerves innervate
  •          rostrolateral part of lower limb
  • Special SensesHypoglossal nerve (CN XII) reaches
  •          tongue
  • Special SensesIntercostal nerves
  • Special SensesLumbar and sacral plexuses
  • Special SensesMusculocutaneous, radial, ulna, and
  •          median nerves enter upper limb bud
  • Special SensesNasal pits face more ventrally, still
  •          widely separated
  • Special SensesNasofrontal groove
  • Special SensesOlfactory fibers connect nasal pits with
  •          brain
  • Special SensesOlfactory fibers enter brain
  • Special SensesOlfactory tubercle present
  • Special SensesPeroneal and tibial nerves innervate
  •          caudomedial part of lower limb
  • Special SensesPhrenic nerve
  • Special SensesPigment in retina visible externally
  • Special SensesPrimordium of cochlear pouch
  • Special SensesTibial nerve innervates foot area
  • Auricular hillocks on hyoid arch
  •          (antitragus and helix)
  • Auricular hillocks on mandibular arch
  •          (tragus and crus)
  • Nervous SystemAlar lamina emerging with dense rhombic
  •          lip
  • Nervous SystemAll cranial nerves identifiable
  • Nervous SystemArchipallium, paleopallium, and
  •          neopallium
  • Nervous SystemArea epithelialis
  • Nervous SystemBrain: Primordial plexiform layer in
  •          area of future temporal lobe
  • Nervous SystemCajal-Retzius cells
  • Nervous SystemCommissure of the trochlear nerve
  • Nervous SystemDiencephalic subthalamic nucleus
  • Nervous SystemDorsal and ventral thalami separated by
  •          groove
  • Nervous SystemDorsal funiculus fibers reach medulla
  •          oblongata
  • Nervous SystemEpiphysis cerebri
  • Nervous SystemGlial cells identifiable adjacent to
  •          neurons
  • Nervous SystemGreater petrosal nerve
  • Nervous SystemInfundibular recess and infundibulum
  • Nervous SystemInterventricular foramen large
  • Nervous SystemMarginal ridge
  • Nervous SystemMedial and lateral ridges of corpus
  •          striatum are continuous
  • Nervous SystemMedian forebrain bundle
  • Nervous SystemNeurohypophysial outgrowth
  • Nervous SystemOlfactory tubercle
  • Nervous SystemPontine flexure deepens
  • Nervous SystemPosterior commissure
  • Nervous SystemRecurrent laryngeal nerve
  • Nervous SystemReticular formation more defined
  • Nervous SystemRetinal fissure closes
  • Nervous SystemSplanchnic nerve
  • Nervous SystemSulcus limitans hippocampi
  • Nervous SystemSuperior laryngeal nerve
  • GeneralFrontonasal prominence
  • GeneralSecond pharyngeal arch more prominent
  • GeneralThird pharyngeal arch recedes
  • (5½ weeks):
  • SkeletalInitial tooth formation
  • (5½ weeks - 6 weeks):
  • MovementSubtle movement begins
  • (5 weeks, 5 days - 7 weeks, 1 day):
  • SkinMelanocytes in epidermis
  •  
  • (5 weeks, 6 days): Carnegie Stage 17
  • SkinFacial growth centers grow and begin
  •          merging forming nose and upper jaw
  • ReproductiveGenital eminence forms phallus or
  •          genital tubercle
  • ReproductiveGonad grows into oval shape with
  •          irregular surface
  • SkeletalAuditory ossicles identifiable in
  •          mesenchyme
  • SkeletalCartilage in occipital sclerotomes (1-4)
  • SkeletalDigital rays in hand plate
  • SkeletalFemur: Chondrification begins
  • SkeletalFoot with rounded digital plate
  • SkeletalHypoglossal foramen (or canal) through
  •          sclerotome 4 (area of future occipital
  •          bone)
  • SkeletalOdontogenic epithelium ermerges in six
  •          areas (four maxillary and two mandibular)
  • SkeletalPrimary palate components (right and
  •          left) fuse in midline
  • SkeletalPrimitive palatine groove
  • SkeletalVertebral centra begin chondrification
  • MuscularPrimordia of orbital muscles
  • Renal/UrinaryCalices
  • Renal/UrinaryMesonephros can produce urine
  • Renal/UrinaryPelvis of the ureter with three main
  •          divisions
  • Renal/UrinaryVesico-urethral canal
  • GastrointestinalBiliary ducts within liver
  • GastrointestinalDorsal and ventral pancreas fuse but
  •          retain separate ducts
  • GastrointestinalDuodenum enlarges proximal to and distal
  •          to bile and pancreatic ducts
  • GastrointestinalEsophagus developing a submucous coat
  •          surrounding epithelium
  • GastrointestinalIntestinal loop begins umbilical
  •          herniation
  • GastrointestinalPrimordial vermiform appendix
  • GastrointestinalStomach regions include gastric canal,
  •          fundus, corpus (or body), and pyloric
  •          antrum
  • RespiratoryTrachea: Precursors of tracheal
  •          cartilages
  • CardiovascularAnterior choroid artery
  • CardiovascularCondensing mesenchyme around junction
  •          between left and right atria and cardiac
  •          tube is precursor to mitral and tricuspid
  •          valves
  • CardiovascularOutflow tract rotates counterclockwise
  • CardiovascularRight and left atrioventricular canals
  •          totally separated
  • Special SensesAll parasympathetic cranial nerve
  •          ganglia identifiable
  • Special SensesAll spinal nerves present
  • Special SensesCell islands in olfactory tubercle
  • Special SensesCrescentic lens cavity
  • Special SensesGeniculate ganglion separate from
  •          vestibulocochlear nerve
  • Special SensesGlobular process emerges from each
  •          medial nasal process
  • Special SensesNasal fin connecting nasal disc and
  •          surface epithelium
  • Special SensesNasofrontal grooves
  • Special SensesOlfactory tubercle with cellular islands
  • Nervous SystemCapillaries between adenohypophysis and
  •          hypothalamus
  • Nervous SystemCommissure of the oculomotor nerves
  • Nervous SystemCortical nucleus in amygdaloid body
  • Nervous SystemDentate and isthmic nuclei in cerebellum
  • Nervous SystemDura begins forming in basal area
  • Nervous SystemEpiphysis cerebri with intermediate
  •          layer
  • Nervous SystemFirst hint of septal nucleus
  • Nervous SystemFrontal and tempororal poles of cerebral
  •          hemispheres
  • Nervous SystemGustatory fibers separate from common
  •          afferent tract
  • Nervous SystemHemispheric stalk
  • Nervous SystemIntermediate layer in tectum
  •          mesencephali
  • Nervous SystemInterventricular foramen
  • Nervous SystemMesencephalon with intermediate layer
  • Nervous SystemSomites: Pairs 38 and 39
  • Nervous SystemSpinal cord reaches caudal tip of body
  • Nervous SystemSubarachnoid space
  • Nervous SystemSynapses in spinal cord between
  •          interneurons and primary afferent neurons
  • Nervous SystemVentral thalamus with intermediate layer
  • (6 weeks):
  • Blood & ImmuneBlood forming in liver
  • SkinMilk lines
  • SkeletalHandplates develop subtle flattening
  • SkeletalMedial skull cartilages: Parachordal,
  •          hypophyseal, and trabecular
  • SkeletalTooth buds (primary teeth)
  • GastrointestinalIntestines fill base of umbilical cord
  • GeneralCrown-heel length 1.6 cm
   
Unit 8:   7 to 8 Weeks
     
  • (7 weeks, 1 day): Carnegie Stage 20
  • SkinFacial processes no longer
  •          distinguishable
  • ReproductiveOvaries full of primitive oogonia,
  •          intermediate pregranulosa cells, and
  •          mesenchyme
  • ReproductiveTestes with short straight tubules
  • SkeletalUpper limbs with slightly flexed elbows
  • MuscularDiaphragm: Central tendon
  • Renal/UrinaryRenal vesicles with S-shaped lumina
  • GastrointestinalSubmandibular gland: Solid epithelial
  •          ducts enlarge and begin to branch
  • CardiovascularAdenohypophysis with new capillaries on
  •          rostral surface
  • CardiovascularScalp vascular plexus
  • Special SensesCochlear duct tip growing horizontally
  • Special SensesLens cavity completely filled
  • Special SensesOptic commissure
  • Special SensesOptic fibers extend to optic chiasma
  • Nervous SystemBrain: Inferior colliculus (in
  •          mesencephalon)
  • Nervous SystemCerebral hemispheres expand beyond
  •          lamina terminalis
  • Nervous SystemCerebral hemispheres extend over
  •          two-thirds of diencephalon
  • Nervous SystemInterpeduncular groove
  • Nervous SystemMedial septal nucleus
  • Nervous SystemNigrostriatal fibers
  • Nervous SystemNucleus of diagonal band
  • Nervous SystemSacrocaudal spinal cord formation
  •          (secondary neurulation) complete
  • Nervous SystemSensory pathways: Cuneate and gracile
  •          decussating fibers
  • Nervous SystemSeptum verum
  • Nervous SystemSpinothalamic tract
  • (7 weeks, 1 day - 8 weeks):
  • GastrointestinalStomach: Folds in stomach wall
  • (7 weeks, 2 days):
  • CardiovascularArteries and veins of heart complete
  •  
  • (7 weeks, 3 days): Carnegie Stage 21
  • SkinVolar pads begin to emerge on fingertips
  • SkeletalChondrocranium with dorsum sellae and
  •          hypophysial fossa
  • SkeletalDens (of second cervical vertebrae)
  • SkeletalWrists slightly flexed
  • GastrointestinalSubmandibular gland: Solid ducts with
  •          definitive branches
  • CardiovascularAnterior and posterior choroid arteries
  • CardiovascularLeft superior vena cava disappears
  •          (Stages 21-23)
  • CardiovascularScalp vascular plexus moving toward
  •          vertex
  • Special SensesCornea: Substantia propria layer
  • Special SensesFibers of optic nerve reach brain
  • Eyelids growing rapidly
  • Nervous SystemAnterior and inferior horns of lateral
  •          ventricle
  • Nervous SystemBrain: Insula within cerebral hemisphere
  • Nervous SystemC-shaped lateral ventricle
  • Nervous SystemCerebral hemispheres cover 75% of
  •          diencephalon
  • Nervous SystemCerebral hemispheres cover more than
  •          half of diencephalon
  • Nervous SystemCortical plate within primordial
  •          plexiform layer
  • Nervous SystemGlial and neurilemmal (Schwann) cells
  •          within cranial nerves
  • Nervous SystemGlobal pallidus internus
  • Nervous SystemInternal fiber layer of cerebellum
  • Nervous SystemLateral olfactory tract
  • Nervous SystemPrimordium of dentate nucleus
  • Nervous SystemPyramidal cells in hippocampus
  • Nervous SystemSubthalamic nucleus proper,
  •          entopeduncular nucleus, and globus
  •          pallidus externus within subthalamus
  • Nervous SystemSulcus transversus rhombencephali
  • Nervous SystemVentral part of lateral geniculate body
  • (7½ weeks):
  • SkinFingertips thicken
  • SkinPlantar pads toes
  • CardiovascularEKG pattern similar to adult
  •  
  • (7 weeks, 5 days): Carnegie Stage 22
  • SkeletalEndolymphatic and jugular foramina
  • SkeletalHands can reach one another and fingers
  •          can overlap
  • SkeletalOptic foramen, foramen rotundum,
  •          internal acoustic foramen
  • SkeletalOsteoblasts emerge
  • Renal/UrinaryLarge glomeruli present within
  •          metanephros
  • GastrointestinalSubmandibular gland: Secondary branching
  •          with lumen formation starting at oral end
  •          of duct
  • CardiovascularChordae tendineae (Stages 22 and 23)
  • CardiovascularIntradural veins (sinuses)
  • CardiovascularScalp vascular plexus 75% of the way to
  •          the vertex
  • Special SensesCochlear duct's second loop growing
  •          upward
  • Special SensesScleral condensation
  • Special SensesTragus and antitragus taking shape
  • Eyelids continue growing rapidly over
  •          the surface of the cornea
  • Nervous SystemBrain: Claustrum
  • Nervous SystemBrain: Cortical plate within cerebral
  •          hemispheres
  • Nervous SystemBrain: Internal capsule with connections
  •          to epithalamus, dorsal thalamus, and
  •          mesencephalon
  • Nervous SystemBrain: Putamen
  • Nervous SystemCerebral hemispheres cover 75% of
  •          diencephalon
  • Nervous SystemCommissural plate thickens
  • Nervous SystemCortical plate expanding rapidly
  • Nervous SystemFolds in roof of third ventricle
  • Nervous SystemNerve fibers between neopallial subplate
  •          and internal capsule
  • Nervous SystemSuperior colliculus
  • Nervous SystemThalamocortical fibers
  •  
  • (8 weeks): Carnegie Stage 23
  • ReproductiveDuctus deferens
  • ReproductiveInterstitial cells forming within testis
  • ReproductiveTesticular tubules
  • EndocrineMale embryos are making testosterone
  •          already!
  • SkeletalAnterior inferior iliac spine
  • SkeletalCostal cartilage
  • SkeletalEnamel organ
  • SkeletalFemur: Head and acetabular fossa
  • SkeletalGlenoid fossa
  • SkeletalGreater trochanter
  • SkeletalHead of humerus
  • SkeletalInguinal ligament
  • SkeletalJoint development: Cavitation underway
  •          in hip, knee, and ankle (in some embryos)
  • SkeletalJoint development: Cavitation underway
  •          in shoulder, elbow, and wrist (in some
  •          embryos)
  • SkeletalNucleus pulposus (from notochord)
  • SkeletalOssification underway in scapula and
  •          distal phalanges in some embryos
  • SkeletalPelvis: Obturator foramen
  • SkeletalPubic symphysis
  • SkeletalScapular spine and notch
  • SkeletalSkull: Foramen magnum (wide)
  • SkeletalSkull: Ossification underway in some
  •          embryos
  • SkeletalSternoclavicular joint and manubrium
  • SkeletalSuperior and inferior pubic rami
  • SkeletalTrachea: Thyroid cartilage
  • SkeletalUlna: Styloid process and olecranon
  • SkeletalVertebrae cartilaginous (33 or 34 in
  •          number)
  • MuscularAnterior digastric muscles
  • MuscularDepressor anguli oris muscle
  • MuscularEsophagus: Longitudinal muscles
  • MuscularGluteus medius and gluteus minimus
  •          muscles
  • MuscularIliacus muscles
  • MuscularMylohyoid and infrahyoid muscles
  • MuscularObliquus superior capitus muscle
  • MuscularObturator externus, gluteus maximus, and
  •          hamstring muscles
  • MuscularObturator internus muscles
  • MuscularOrbicularis oculi muscles
  • MuscularPosterior belly of the digastric muscle
  • MuscularPsoas tendon
  • MuscularRectus femoris muscle
  • MuscularRectus sheath with anterior and
  •          posterior lamina
  • MuscularTemporal and lateral pterygoid muscles
  • MuscularZygomaticus major muscle
  • Renal/UrinaryBladder: Muscularis layer
  • Renal/UrinaryKidneys at level of first three lumbar
  •          vertebrae
  • Renal/UrinaryMetanephros: Numerous large glomeruli
  • Renal/UrinaryMetanephros: Secretory tubules
  •          elongating and becoming convoluted
  • Renal/UrinarySinusal tubercle
  • Renal/UrinaryUrethra
  • GastrointestinalGastrolienal ligament
  • GastrointestinalNerves reaching intestinal loop
  • GastrointestinalSubmandibular gland: Lumen present in
  •          terminal portions of duct
  • GastrointestinalSubmandibular gland: Mesodermal sheath
  •          surrounds gland
  • GastrointestinalUnfused uvula (edge of unfused palatine
  •          shelf) and secondary palate
  • RespiratoryCostodiaphragmatic recess of pleural
  •          cavity
  • RespiratoryLingula of left upper lobe
  • RespiratoryPseudoglandular stage begins
  • CardiovascularAzygos vein
  • CardiovascularBlood supply to the brain closely
  •          resembles adult pattern
  • CardiovascularHemiazygos veins
  • CardiovascularInferior epigastric artery
  • CardiovascularInferior vena cava valve at junction of
  •          right atrium
  • CardiovascularPericardial sac
  • CardiovascularScalp vascular plexus nearing vertex
  • CardiovascularSubmandibular glands: Angiogenesis
  •          begins around epithelial tree (ducts)
  • CardiovascularSuperior sagittal sinus
  • Special SensesCochlear duct's 2.5 coils nearly
  •          complete
  • Special SensesCranial nerve distribution mimics adult
  •          pattern
  • Special SensesEye: Secondary vitrous body
  • Special SensesLens: Secondary lens fibers emerging
  • Special SensesRetina: Eight layers present
  • Special SensesRetina: Four of the ten adult layers
  •          present
  • Special SensesTympanic membrane
  • Eyelids fusing laterally and medially
  • Optic tract reaches ventral portion of
  •          lateral geniculate body
  • Nervous System"The rhombencephalon...presents striking
  •          resemblance to that of the newborn."
  • Nervous SystemAmygdala area
  • Nervous SystemBrain represents 43% of embryo
  • Nervous SystemBrain: Caudate nucleus and putamen
  •          within corpus striatum
  • Nervous SystemCerebellar commissures
  • Nervous SystemCerebellum with external germinal layer
  • Nervous SystemCerebral hemispheres cover lateral
  •          portion of diencephalon
  • Nervous SystemChoroid plexus now lobular
  • Nervous SystemCortical plate covers nearly all of
  •          neopallial surface
  • Nervous SystemDura lines entire vertebral canal
  • Nervous SystemFasciculus cuneatus and fasciculus
  •          gracilis form the decussation of the
  •          medial lemnisci
  • Nervous SystemGreater palatine nerve
  • Nervous SystemGrey and white matter
  • Nervous SystemHippocampus reaches temporal pole
  • Nervous SystemInferior and superior cerebellar
  •          peduncles
  • Nervous SystemMost cisterns present
  • Nervous SystemPrincipal nucleus of inferior olivary
  •          nuclei
  • Nervous SystemPyramidal decussations
  • Nervous SystemRight- and left-handedness emerges
  • Nervous SystemSuprapineal recess
  • Nervous SystemSuprascapular nerve
  • Nervous SystemVermis of cerebellum
  • GeneralCrown-heel length 4.3 cm
   
Unit 10:   9 to 10 Weeks
     
   
Unit 12:   11 to 12 Weeks
     
   
Unit 14:   4 to 5 Months
     
  • (18 weeks):
  • SkinApocrine sweat glands
  • SkinSweat glands
  •  
  • (19 weeks):
  • SkinMelanin production
  • Nervous SystemSulci on surface of cerebral hemispheres
  •  
  • (20 weeks):
  • GastrointestinalPeyer's patches
  • RespiratorySurfactant production (low levels)
  • GeneralCrown-heel length 28 cm
  • GeneralHead circumference 20 cm
   
Unit 16:   6 to 7 Months
     
  • (25 weeks):
  • GastrointestinalIntestinal lining contains all adult
  •          cell types
  •  
  • (26 weeks):
  • RespiratoryTerminal sac stage begins
  •  
  • (28 weeks):
  • GeneralCrown-heel length 39.5 cm
   
Unit 18:   8 to 9 Months
     
  • (36 weeks):
  • RespiratorySurfactant production accelerates
  • GeneralBrain weight 300 grams
  • GeneralCrown-heel length 48.5 cm
   


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