16 



MORPHOLOGY OF THE 



here in coils together with the ileum, caecum, and a portion 

 of the colon. The colon may be traced into the abdominal 

 cavity proper, where it takes its position just to the left of 

 the median line of the body. 



As we have already seen, the presence of the intestines 

 within the cavity of the umbilical cord is chiefly due to a 

 rapid and tremendous growth of the liver. Unfortunately, 

 it has been impossible for me to determine the exact force, 

 or conditions, which cause their entrance into the abdominal 

 cavity. The period of their entrance is certainly a very 

 variable one, and, indeed, one is tempted to think that it is 

 almost ungoverned by the size or the length of the embryo, 

 and possibly only by a certain stage of development. At one 

 time it seemed to me as though it might possibly be ex- 

 plained by means of the mesenteric attachment. The 

 mesenteries of a 15 mm. embryo have exactly the same 

 attachment as in the adult cat. It is a curious fact that, 

 were it possible to exert traction upon that part of the jeju- 

 nal loop which crosses the third portion of the duodenum on 

 its way to the cavity of the umbilical cord, and should this 

 be continued until the jejunum, ileum, caecum, and colon 

 were drawn within the abdominal cavity proper, and then 

 if at a given moment this traction should cease, one would 

 find the intestines arranged as they are in the adult animal, 

 with this exception, that the caecum and colon, being the 

 last to enter the abdomen, would naturally lie ventrad from 

 the other coils of intestine, whereas in the adult cat they lie 

 dorsad from them. And not only this, but the arrangement of 

 the mesenteries would be found to be identical with those of 

 the adult cat. Although it is impossible to give at present the 

 reason of the entrance of the intestines into the abdomen, it 

 is my belief that they have a definite order of entrance, and 

 obviously it cannot be the theoretical one just described, 

 although it seems to me possible that at some later date 

 this order may be found to be applicable to the human em- 

 bryo. 



Fig. 10 represents the dissection of an embryo 62 mm., 



