248 Professor Clark on a Case 



The human placenta is developed when the umbilical vesicle 

 begins to disappear: and what it is that determines the part of 

 the uterus on which it is formed has been already described. 

 The subdivisions of the umbilical vessels distribute themselves 

 essentially to those tufts of the exochorion which are in the region 

 where the decidua was reflected. The tufts gradually grow to- 

 gether in the third and fourth months of pregnancy, and thus 

 the foetal placenta is smooth on its inner surface and presents 

 numerous inequalities on the external : which inequalities are the 

 several collections of the prolonged and subdivided villi of the 

 exochorion. On every one of the villi as a stem, and on all 

 their subdivisions as branches, are distributed corresponding- sub- 

 divisions of the umbilical vessels which directly anastomose. 



As the abdomen gradually closes the only opening left is the 

 navel, which is near the tail end. The umbilical cord consists 

 externally of a layer from the amnion, which passes from the 

 cuticle of the foetus : beneath this is the vascular sheath originally 

 derived from the allantois, which on the one hand is lost in the 

 aponeurosis of the abdominal muscles, on the other in the endo- 

 chorion. It immediately surrounds the vessels, as well as the layer 

 of cellular membrane which they derive from the peritoneum, and 

 which with the vessels contains also a gelatinous fluid, gradually 

 to be absorbed by the foetus, and called the gelatine of Wharton. 

 Thus the original external membrane of the ovum, the exochorion, 

 has at no time any direct connection with the cord, or with the 

 embrvo*. 



* Besides these parts the cord at the earliest period of its formation, when it is wide 

 towards the abdomen, contains a loop of intestine, the umbilical vesicle, and the allantois. 



