THE FCETAL MEMBRANES OF MAN. 



245 



- h 



x- am 



(the allantois), and conducts the allantoic blood-vessels from the 

 pelvic portion of the intestine to the chorion. 



This cord is a characteristic structure for the human embryo, the 

 significance of which is still in dispute. KOLLIKER and His have 

 given somewhat different explanations of it. KOLLIKER brings the 

 cord into relation with the development of the allantois. He makes 

 the fundament of this important embryonic appendage arise, as in 

 other Mammals, from the hind gut of the embryo, and approach the 

 serosa as a thick vascular connective-tissue growth lined with a narrow, 

 short epithelial 

 tube, without 

 previously de- 

 veloping inside 

 itself a large 

 epithelial sac. 

 He also main- 

 tains that the 

 connective- 

 tissue part of 

 the short allan- 

 toic cord, or 

 bell y-s talk, 

 grows around 

 on the whole 

 inner side of 

 the serosa, and 

 into the epi- 

 thelial villi. 



His regards 

 as unwar- 

 ranted " the 



assumption, in opposition to the actual state of affairs, that the 

 human embryo at first separates itself from, the part of the blasto- 

 dermic vesicle which is employed for the chorion, and subsequently 

 unites with it again by means of the fundament of the allantois." 

 He does not admit that the fundament of the embryo in Man is 

 ever wholly constricted off from the chorion, as in the remaining 

 Mammals, and he recognises in the belly-stalk " the bridge of 

 connection between the fundament of the embryo and the 

 chorionic part of the original blastodermic vesicle, which has 

 never been severed." According to . him the allantois in the 



Fig. 141. Human embryo with yolk-sac, amnion, and belly-stalk of 

 15 to 18 days, aftei COSTE, from His ("Menschliche Embryonen"). 



His has untwisted somewhat the posterior end of the body in com- 

 parison with the original figure, in order to bring into view the 

 right side of the end of the body, the left side being represented 

 in COSTE'S fig. 4. The chorion is detached at am 1 , am, Amnion ; 

 am 1 , the point of attachment of the amnion to the chorion drawn 

 out to a tip ; bst, belly-stalk ; Sch, tail-end ; us, primitive seg- 

 ment ; dg, vitelline blood-vessels ; ds, yolk-sac ; h, heart ; vb, 

 visceral arch. 



