662 



RODENTS AND RABBITS 



XXV. 4- 



may be only superficial. The two orders are kept together in one cohort 

 Glires, more as a convenience than because of characters they have in 

 common. The arrangements for gnawing found in the lagomorphs 

 have indeed a superficial similarity to those of rodents, but on inspec- 

 tion the differences appear profound. Continually growing incisors 



Fig. 435. a. Diagram of stomach of Lepus: dashes, cardiac zone; dots, fundus; 

 crosses, pyloric glands. B. L.S. of rabbit stomach, c. Diagram showing the passage 

 of food and caecotrophs traversing the digestive tracts. In the stomach, under the 

 mechanical action of peristalsis the caecotrophs are mixed with the food. In the lowest 

 part of the caecum, the chyme under the action of bacteria is made into caecotrophs, 

 which the animal eats soon after they are expelled from the anus. 



ca. caecotrophs; cae. caecum; cr. waste pellets; ma. alimentary mass; oe. oesophagus; 



p. pylorus; za. zone where the caecotrophs are mixed with the alimentary mass; zc. zone 



of formation of caecotrophs. (b. and c. after W. Harder.) 



are present in both groups, but in lagomorphs the upper pair is accom- 

 panied by a small second pair (hence 'Duplicidentata'). The diastema is 

 common to the two groups, and both have cheek pouches with similar 

 functions. The similarity of the molariform teeth is only superficial, 

 however; in the lagomorphs three premolars remain in the upper jaw 

 and two in the lower. The premolars and the molars all acquire sharp 

 transverse ridges, usually two each, used for cutting rather than 

 grinding, the upper teeth biting outside the lower ones, not inside as 

 in rodents. The masseter is powerful, but simpler than in rodents, and 

 it does not extend into the infra-orbital canal. The temporalis muscle 



