ALIMENTARY TRACTS AND ADJACENT GLANDS 95 



is divisible into two tracts — the duodenum and Meckel's 

 tract (see Mitchell, 1905) — not into three as in man. In 

 this genus the two tracts are not differentiated save by 

 means of the mesentery. Without undue extension the 

 length of the small intestine, between the stomach and 

 caecum, was 655 mm. in one specimen and 725 in another. 

 The collapsed width of the duodenal portion was about 

 7 mm. 



In three specimens of Neotoma the length of the small 

 intestine was 480, 520, and 490 mm. In Teonoma it was 

 much more capacious. The duodenal width was 12 to 13 

 mm., although farther caudad it was not quite so broad; 

 and its length in two specimens was 815 and 825 mm. 



Liver. The medial lobe of the liver is the largest. It 

 is divisible into a right (the larger) and a left lobelet, be- 

 tween which is situated the gall bladder. In Homodon- 

 tomys the medial border of the left lobelet lay superficial 

 to that of the right in two specimens, while in two each of 

 Neotoma and Teonoma the opposite condition obtained. 

 The left lateral lobe is relatively smaller in Homodontomys 

 and Neotoma than in Teonoma, but in the last it is almost 

 if not quite as large as the medial lobe. The right lateral 

 lobe is smaller still, and is divisible into a cranial (the 

 larger) and a caudal lobelet. The flat, caudal lobe lies 

 dorsad of the left lateral and is usually double, but was 

 observed to be single in one individual of Homodontomys. 

 In two specimens of each subgenus the cubic capacity of 

 the liver was found to be constantly about 5 cc. in Homo- 

 dontomys) 6.5 cc. in Neotoma; and 12 cc. in Teonoma. The 

 precise functions of the liver are too involved and as yet too 

 poorly understood for any interpretation of the significance 

 of the much larger size of this organ in Teonoma. Suffice 

 it to say that it probably reflects some detail regarding the 

 normal diet. 



Large intestine. The most interesting part of this is the 



