Reproduction
635
Placenta
Uterus
Urinary bladder
Pubic bone
Urethra
Vagina
Cervix
Rectum
(a)
(b)
Amniotic sac
Cervix
Vagina
Placenta
(c)
Ruptured
amniotic sac
Amniotic
fluid
(e)
(d)
Placenta
Placenta
(partially detached)
Uterus
Umbilical cord
Figure 17–30
Stages of parturition. (a) Parturition has not yet begun. (b) The cervix is dilating. (c) The cervix is completely dilated, and the fetus’s head is
entering the cervical canal; the amniotic sac has ruptured and the amniotic fl uid escapes. (d) The fetus is moving through the vagina. (e) The
placenta is coming loose from the uterine wall in preparation for its expulsion.
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