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Prenatal Form and Function – The Making of an Earth Suit


Unit 9:   8 to 9 Weeks

  Closer Look: 
  Applying the Science: 
Play Movie - Human fetus 8 to 9 weeks
Movie 9.1 - 8 to 9 Weeks
Play Movie - Fetal Period Begins
Movie 9.2 - Fetal Period Begins

Pacifiers sometimes work well after birth, however, in the womb the embryo often discovers a thumb works best.

By the beginning of the fetal period, synapses, or connections between nerve cells, are found within the cerebral cortex.1 The fetal period continues until birth.

Play Movie - Thumb Sucking Begins
Movie 9.3 - Sucking and Swallowing
mother kissing newborn baby on cheek
A soft kiss on the face evokes the slightest smile from this newborn whose ability to sense light touch over her arms and legs began just 9 weeks after fertilization.


By 9 weeks thumb sucking2 begins and the fetus may swallow amniotic fluid.3 The fetus can also grasp an object,4 move the head forward and back, open and close the jaw, move the tongue, sigh,5 and stretch.6

baby grasping
By 9 weeks the fetus will grasp an object, an action we continue to see in newborns and small children exploring the world about them.
Play Movie - Motion and Sensation
Movie 9.4 - Motion and Sensation

By 9 weeks, the nerve receptors in the face, palms of the hands, and soles of the feet can sense and respond to light touch.7 Following a light touch on the sole of the foot, the fetus will bend the hip and knee and may curl the toes.8

Baby Foot, Feet
Similar to a child having his foot tickled, the 9-week fetus will withdraw if the sole of the foot is lightly touched.
8 weeks 2 day Fetus Foot, Feet
Figure 9.1 - Foot
The Biology of Prenatal Development DVD
Copyright © 2006 EHD, Inc. All rights reserved.

mother daughter, smiling
Long before birth, the female fetus is already developing reproductive cells which may one day help form yet another generation.

The eyelids fuse completely shut by 9 weeks.9

The peristalsis previously restricted to the large intestine begins in the small intestine.10


In female fetuses the uterus is identifiable by 9 weeks11 and, within the fetal ovary, immature germ cells called oogonia, are replicating via mitosis.12 Outside the body, the genitalia begin to differentiate as either male or female.13


In the larynx, the appearance of vocal ligaments signals the onset of vocal cord development.14

Play Movie - Live Long and Prosper
Movie 9.5 - Live Long and Prosper
Play Movie - Vocal Cord Development
Movie 9.6 - Vocal Cord Development
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1 Molliver et al., 1973. 404, 406.
2 Liley, 1986. 13; Liley, 1972. 103.
3 Campbell, 2004. 24; Cunningham FG et al., 2001. 149; de Vries et al., 1982. 311; Petrikovsky et al., 1995. 605.
4 Robinson and Tizard, 1966. 52; Valman and Pearson, 1980. 234.
5 de Vries et al., 1982. 305-307.
6 de Vries et al., 1982. 311.
7 Humphrey, 1970. 16-17; Humphrey, 1964. 96; Humphrey and Hooker, 1959. 77-78; Reinis and Goldman, 1980. 232.
8 Robinson and Tizard, 1966. 52; Valman and Pearson, 1980. 234.
9 Andersen et al., 1965. 648-649; Moore et al., 2000. 53-54; O'Rahilly and Müller, 2001. 465; Pearson, 1980. 39-41.
10 Cunningham et al., 1997. 169.
11 O'Rahilly, 1977a. 128; O'Rahilly, 1977b. 53; O'Rahilly and Müller, 2001. 327.
12 Blackburn, 2003. 7; O'Rahilly and Müller, 2001. 25, 322.
13 Campbell, 2004. 28, 35; Moore and Persaud, 2003. 315; O'Rahilly and Müller, 2001. 336.
14 Campbell, 2004. 29; O'Rahilly and Müller, 1984. 425.