88 DEVELOPMENT OF THE HUMAN EMBRYO. 



2. In the human subject.* 



Allantois. Bischoff \ inclines to the same view of the development and 

 office of the allantois of the human embryo, as was maintained by Professor 

 Miiller { and many other embryologists, namely, that, as is the case in the 

 embryo of rodent animals, it is developed merely as a narrow vesicle which 

 elongates itself till it reaches the chorion, and is only destined to conduct 

 the umbilical vessels to that structure, having done which, it disappears, 

 the urachus of the urinary bladder being its only remains. In further re- 

 futation of the opinion of Velpeau and other anatomists who consider that 

 after its formation, the allantois increases rapidly, and as in ruminants, sur- 

 rounds the embryo together with its amnion and umbilical vesicle, uniting 

 by one of its layers with the chorion, by the other with the amnion, 

 Bischoff draws attention to three principal circumstances which are opposed 

 to this view. First, no one has yet observed the smallest trace of the 

 allantois, either on the internal surface of the chorion, or on the external 

 surface of the amnion ; both the chorion and amnion are perfectly simple 

 membranes. Secondly, in all cases in which the allantois applies itself 

 upon the other membranes of the embryo, it furnishes these with vessels, so 

 that in pachyderms, ruminants, and Carnivora in which the allantois is thus 

 disposed, the chorion and amnion are at a certain period, richly supplied 

 with vessels ; but in the human ovum nothing like this occurs, no vessels 

 at any period of its existence are ever found in either of these membranes, 

 except at that part where the allantois comes into contact with the chorion 

 and at which the placenta is subsequently developed. Thirdly, if, as as- 

 sumed, the allantois in its development passes at all parts between the 

 chorion and amnion, it imist necessarily invest the umbilical vesicle, on one 

 side or the other ; but this is never found to be the case. 



So far as concerns the refutation of Velpeau's hypothesis, the account 

 of the human allantois recently published by Dr. Max Langenbeck 

 accords with that of Bischoff. But Langenbeck has proceeded further 

 and has given a more satisfactory explanation of the probable nature and 

 ultimate condition of this structure than has been afforded by any previous 

 physiologist. His researches shew that the allantois at an early period 

 comes into immediate relation with the Wolffian bodies in this agreeing 

 withKeichert in his observations on the chick || and, moreover, is concerned 

 more directly, and in a different manner than has yet been described, in the 

 formation of the urinary bladder. At its first development the allantois of 

 the human embryo appears, as has been described by others, in the form of 



* Miiller's Physiology, p. 1572. 



t Entwick. der Saugeth. und des Menschen, p. 129. J Physiology, p. 1582. 



Untersuchungen liber die Allantois. Gottingen, 1847. 

 Miiller's Physiology, p. 1554. 



