18 



MORPHOLOGY OF THE 



turn is more developed, and that the spleen is situated much 

 farther to the left side of the body. In a word, this embryo 

 represents a more advanced stage of development than the 

 previous ones. The jejunum forms a long, extensive loop, 

 which, together with its mesentery, almost completely con- 

 ceals the duodenum. The ca3cum lies in the median line of 

 the body, close to and caudad from the pyloric extremity of 

 the stomach. The terminal portion of the ileum takes a 

 straight course to the umbilicus, where it joins the remaining 

 portion of the small intestine to form the numerous coils con- 

 tained within the cavity of the umbilical cord. The colon 

 descends, makes a curve with its convexity to the left, and 

 lies between the kidney and the jejunal loop, and close to its 

 termination seeks once more the median line of the body. 

 In this plate the outline of the caecum is not distinctly de- 

 fined, on account of its position. It lies with its mesenteric 

 border facing dorsad, and this would seem to be the most 

 natural position for it to occupy directly after its entrance 

 into the abdominal cavity. 



It will be remembered that in the former embryo the 

 jejunum formed a short loop ventrad from the duodenum, 

 and that the ca3cum was extra-abdominal. In this embryo 

 the jejunal loop is much more extensive, and the caecum is 

 intra-abdominal as well as the colon, and a short stretch of 

 the ileum. The extra length of the jejunal loop approxi- 

 mately corresponds to the length of the colon, caecum, and 

 ileum which were previously extra-abdominial; hence it 

 seems reasonable to conclude that the first step in the en- 

 trance of the intestine is a simultaneous entrance of its 

 extremities. 



It has been my fortune to observe several embryos whose 

 intestines were entirely intra-abdominal, with the exception 

 of a small coil of the ileum, which was situated from one to 

 three cm. from the caecum. These embryos varied greatly 

 in size, and the variation is quite sufficient to account for 

 the range of from one to three cm. 



Hence we conclude that there exists in the cat a definite 



