TBE FCETUS. 



1023 



allantoid cavity, it becomes detached, like certain fibrous or cartilaginous bodies 

 in the synovial or serous cavities ? " (F. Lecoq). 



According to Dastre, the hippoiuanes arise between the chorion and the 

 allantois, and they are formed by the phospliatic matter of the chorion, wliich 

 collects in masses at certain points, where it is enveloped by a mass of the sub- 

 jacent mucous connective substance of this membrane. 



4. The Umbilical Vesicle. 



The iimhilical vesicle is a small fusiform or pyrifonn pouch, lodged in the 

 infundibulum at the extremity of the umbilical cord. Its fundus adheres to 

 the chorion ; the opposite extremity is prolonged to a variable depth in the 

 substance of the cord, and is even continued — in the very young foetus — to the 

 abdominal cavity, by a narrow canal that communicates with the terminal 

 portion of the small intestine. 



This pouch has a red colour, due to its great vascularity. Its walls receive a 

 special artery derived from the anterior mesenteric, its corresponding vein passing 

 to the portal vein. These are the two omphalo-imsenteric vessels. 



In the last months of foetal life, the lunbilical vesicle is always more or less 

 atrophied ; its cavity has disappeared, and it is nothing more than a thin reddish- 

 brown cord. Its vessels also become 



atrophied in the same manner, and nearly F'g- 558. 



always nothing else is found than the 

 artery, reduced to the dimensions of a 

 thread. 



PORTION OF THE ULTIMATE RAMIFICATIONS 

 OF THK UMBILICAL VI:SS1:LS, FORMING THE 

 FOiTAL VILLI OF THE PLACE.NTA. 



5. The Placenta (Figs. 556, 558, 559). 



The placenta is the organ wliich 

 establishes relations between the foetus 

 and the uterus of the parent. It ad- 

 heres to the chorion, of which it is only 

 a kind of dependency. 



In Solipeds, the placenta is composed of a multitude of small tubercles 

 (placent(c), spread uniformly over the external surface of the chorion, which they 

 almost completely cover. Their number and development are greatest in the 

 middle portion of the chorion — in the zone where the principal divisions of the 

 umbilical cord lie beside this membrane. Thence they diminish towards the ex- 

 tremity of the uterine cornua and body. In front of the openings of the uterus — 

 Fallopian tubes and os uteri — they are rare. These small tubercles are formed by 

 an aggregation of extremely vascular vilh, which implant themselves in the follicles 

 of the uterine mucous membrane. The terminal ramifications of the vessels of 

 the cord constitute the vascular apparatus of these viUi (Figs. 558, 559, 560). 



The parts of the uterine mucous membrane which are related to the foetal 

 placentae, are named the uterine or maternal placetrt(v. They are constituted l)y 

 follicular cavities, which are formed beside permanent glandular follicles in the 

 mucous membrane during gestation, but they disappear after parturition 

 (Ercolani). 



This Italian anatomist compared the cavities of the maternal placentae to 

 glands which secrete a kind of uterine milk. Laulanie, from a study of the 

 maternal placenta of the Guinea-pig — and which he regards as a colossal multi- 



