470 ZOOLOGY SECT. 



claws which may be retractile into a sheath. The first digit of 

 the maims and the first and fifth of the pes are never longer than 

 the others. One tooth on each side in each jaw the last pre- 

 niolar in the upper jaw and the first molar in the lower is always 

 modified to form the carnassial or sectorial tooth with a cutting 

 edge which bites against the edge of the opposed tooth. 



This sub-order comprises the Cats (Felidce), Civets (ViverridcB), 

 Hyaenas (Hycenidce), Dogs (Canidce), Bears (Ursidce), Weasels 

 (Mustelidce), and Otters (Lutridce). 



Sub-order b. Pinnipedia. 



Carnivora in which the limbs are adapted to an aquatic life, the 

 proximal segments being short, the distal elongated and webbed 

 between the digits ; with five well-developed digits in each manus 

 and pes, the first and fifth of the pes being larger than the others. 

 The number of incisors is reduced, and there are no carnassials. 

 The cerebral hemispheres are very richly convoluted. 



This order includes the Eared Seals (Otariidce), the Earless Seals 

 (Phocidce), and Walruses (Trichechidcs). 



\ 



ORDER 6. RODENTIA. 



Vegetable-feeding Eutheria, mostly of small size, with furry 

 (sometimes spiny) integument, clawed digits, and usually planti- 

 grade limbs. A clavicle is usually present. The dentition is 

 diphyodont ; there are no canines, and there are never more than 

 two incisors in the lower jaw and usually only two in the upper 

 all elongated, chisel-like, and growing from persistent pulps ; the 

 premolars and molars are usually few, and in many cases grow 

 from persistent pulps. There is a large csecum. The cerebral 

 hemispheres have in most instances smooth surfaces, and do not 

 much overlap the other parts of the brain. The testes are retained 

 in the abdomen or descend to the groin. The uterus is two-horned 

 or double. The placenta is deciduate and disc-shaped (discoidal). 



This extensive order includes the Rats and Mice (Muridce), 

 Hares and Rabbits (Leporidce), Squirrels (Sciuridce), Jerboas 

 (Dipodidce), Beavers (Castoridce), and Porcupines (Hystricidce). 



ORDER 7. INSECTIVORA. 



Small insectivorous Eutheria with the nose usually produced 

 into a short soft muzzle, with furry (sometimes spiny) integument, 

 clawed digits, and usually pentadactyle plantigrade limbs. The 

 dentition is diphyodont and complete, and all the teeth are rooted ; 

 the incisors are small ; there are never fewer than two incisors on 

 each side of the lower jaw ; the molars are small and provided 

 with pointed cusps. A clavicle is present. The brain is simple 



