38 Zoology of Colorado 



footed mouse of a different genus (Apodemus), which I obtained 

 on the Kudia River in Siberia, showed a similar ratio; large 

 intestine 14.5 cm., small 35 cm. 



Other interesting features are found in the caecum or blind 

 sac at the junction of the large and small intestines. It is the 

 reduced portion of this which is known in man as the vermiform 

 appendix, and is the seat of appendicitis. In the house mouse, 

 musk-rat and mountain rat the enlarged sac extends beyond the 

 point where the small intestine enters it, and invades the begin- 

 ning of the large intestine. In the house mouse the transition to 

 ordinary large intestine is gradual, but in the other two it is 

 abrupt. In the musk-rat and mountain rat the caecum is very 

 long; in the rock squirrel and Colorado chipmunk (Eutamias 

 quadrivittatus) it is much shorter and broader. In the white- 

 footed mice the caecum is larger than in the house mouse (Mus), 

 but does not invade the large intestine, Striking differences 

 were found between the species of white-footed mice, but we do 

 not know whether they would be constant in larger series. Thus 

 Peromyscus rowleyi showed a caecum about 34 mm. long and 

 comparatively narrow; in P. rufinus it was much shorter and very 

 broad; in P. nasutus it was extremely short and broad, with a 

 large rounded extension beyond the beginning of the large intestine, 

 but not invading it. A similar gibbous basal extension, not so 

 large, was found in the kangaroo rat, Perodipus montanus. The 

 stomach in the three species of white-footed mice just mentioned 

 showed a constriction separating the pyloric end from the remain- 

 ing portion. In our only specimen of the grasshopper mouse, 

 Onychomys palkscens, there was a double constriction, producing 

 a tri-partite stomach. But in the house mouse, Norway rat, 

 kangaroo rat, chipmunk (Eutamias operarius), guinea-pig, musk- 

 rat and rock squirrel there is no constriction at all. The porcupine 

 (Erethizon) was examined by Printz, and he found a sac with a 

 basal constriction at the pyloric end, but not leading to the 

 duodenum, being in fact a sort of pyloric caecum. The heart, 

 lungs, and liver are no less interesting. Thus in Onychomys 

 palkscens the right inferior lobe of the lungs has a small pointed 

 lobule (lobulus azygos) beneath. The same is true of Peromyscus 

 rowleyi and Eutamias quadrivittatus, but the lobule is absent in 

 Perodipus montanus. 



