AND ITS APPENDAGES. 647 



first, as we have shown above, a hollow sac ; but, as it spreads out 

 over the surface of the investing membrane of the egg, its two 

 opposite walls adhere to each other, so that its cavity is obliterated 

 at this situation, and it is thus converted into a single vascular 

 membrane, the chorion. This obliteration of the cavity of the 

 allantois commences at its external portion, and gradually extends 

 inward toward the point of its emergence from the abdomen. The 

 hollow tube, or duct, which connects the cavity of the allantois with 

 the posterior part of the intestine, is accordingly converted, as the 

 process of obliteration proceeds, into a solid, rounded cord. This 

 cord is termed the urachus. 



After the walls of the abdomen have come in contact, and united 

 with each other at the umbilicus, that portion of the above duct 

 which is left outside the abdominal cavity, forms a part of the um- 

 bilical cord, and remains connected with the umbilical arteries and 

 vein. That portion, on the contrary, which is included in the ab- 

 domen, does not close completely, but remains as a pointed fusiform 

 sac, terminating near the umbilicus in the solid cord of the urachus, 

 and still communicating at its base with the lower extremity of the 

 intestinal canal. This fusiform sac (Fig. 241, e), becomes the uri- 

 nary bladder ; and in the foetus at term, the bladder is still conical 

 in form, its pointed extremity being attached, by means of the ura- 

 chus, to the internal surface of the abdominal walls at the situation 

 of the umbilicus. Afterward, the bladder loses this conical form, 

 and its fundus in the adult becomes rounded and bulging. 



The urinary bladder, as it appears from the above description, at 

 first communicates freely with the intestinal cavity. The intestine, 

 in fact, terminates, at this time, in a wide passage, or cloaca, at its 

 lower extremity, which serves as a common outlet for the urinary 

 and intestinal passages. Subsequently, however, a horizontal par- 

 tition makes its appearance just above the point of junction between 

 the bladder and rectum, and grows downward and forward in such 

 a manner as to divide the above-mentioned cloaca into two parallel 

 and unequal passages. The anterior or smaller of these passages 

 becomes the urethra, the posterior or larger becomes the rectum ; 

 and the lower edge of the septum between them becomes finally 

 united with the skin, forming, at its most superficial part, a tole 

 rably wide band of integument, the perineum, which intervenes 

 between the anus and the external portion of the urethra. 



The contents of the intestine, which accumulate during foetal life, 

 vary in different parts of the alimentary canal. In the small intes- 



