THE WAY LIFE BEGINS 69 



follow, some aspects of which, indeed, do not become 

 apparent until maturity. 



Birth 



The outer surface of the egg, immediately after fertiliza- 

 tion, throws out processes which enter the walls of the uterus 

 much as though it were a parasite. As soon as this is done 

 the surface of the egg grows rapidly, so that it becomes an 

 envelop about the embryo which occupies, at the outset, but 

 a relatively small space in the interior. The embryo is 

 attached to the inner wall of the now very much expanded 

 egg by means of a stalk, through which the blood courses to 

 and from the mother as soon as the yolk with which the 

 embryo is supplied is used. The stalk then becomes the 

 navel, or umbilical cord. The villi, or processes which have 

 entered the uterus, withdraw from all portions of the envelop 

 except in the neighborhood of the stalk attachment of the 

 embryo. (Plate IX.) Here they enter more deeply into the 

 uterus and make a circular disk of soft, spongy texture, six or 

 eight inches in diameter and perhaps an inch thick, known as 

 the placenta. 



There is no direct connection between the blood of the 

 mother and that of the growing child. The nutritive serum 

 from the mother is deposited in the placental region of the 

 uterus and there absorbed by the many terminal blood vessels 

 leading through the umbilical cord to the placenta. All of 

 the higher animals have placentas, those of the higher apes 

 and man being almost identical, but the mammals showing 

 different sizes and shapes. 



As the time for birth approaches, the child takes up a 

 position with its head toward the outlet. The muscular walls 

 of the uterus have thickened and grown. By rhythmic con- 

 traction, sometimes long continued, the head of the child is 

 forced through the two envelops which have sheltered it 

 through nine long months, at the same time freeing the fluid 

 within the inner one. The pelvic bones are stretched apart 

 and the child makes its way through the vaginal canal to 

 the outside. It brings with it the cord of blood vessels, which 



