98 



HUMAN EMBKYOLOGY AND MOEPHOLOGY. 



reflexa atrophy, and in this way the discoidal placenta of man is 

 formed. In lower primates (Monkeys) there are two discs 

 (bi-discoidal), and this form occasionally occurs in man. 



vein 



artery 



artery 



muscular coat 

 blood spaces 

 vein 



chorionic villus 

 deeidua serotina 



chorion 

 amnion. 



deeidua vera 

 deeidua reflexa 



cervix. 



Fig. 76.— Showing the arrangement of the Amnion, Chorion, and Deeidua in the 3rd 

 month and the Formation of the Placenta. 



The elements entering into the formation of the placenta are 

 «liagrammatically shown in Fig. 77. They are : 



1st. The deeidua serotina, formed from the mucous membrane 

 of the uterus. 



2nd. The prechorion, from the somatopleure. 



3rd. The allantois from the splanchnopleure. 



4th. The amnion from the somatopleure. 



