RODENTS 867 



developed. The intestine has a large caecum, except in 

 Myoxidae. Special anal or perineal or other glands secreting 

 odoriferous substances are frequent. 



The testes are inguinal or abdominal ; only in the hares 

 and rabbits do they completely descend into scrotal sacs. 



The mammae are on the abdomen, or on the abdomen 

 and thorax. The uterus is double or very markedly 

 bicornuate. There is a provisional yolk-sac placenta ; the 

 allantoic placenta is discoidal and deciduate. 



The Rodents are very widely distributed, but are most abundant in 

 S. America, where they form a very characteristic part of the fauna. 

 Out of seventeen existing famiUes, nine are represented there, and four 

 are pecuHar to it. 



The Rodents are divided into four sub-orders :— 



1. Sciuromorpha. — Squirrels {Sciurus), marmots (Arctomys), 



prairie-dogs (Cynomys), and beavers {Castor). 



2. Myomorpha. — Rats and mice {Mus), voles (Arvicola), lemmings 



(Myodes), and jerboas (Dipus). 



3. Hystricomorpha. — Porcupines [Hystrix), agoutis (Dasyprocta), 



guinea-pigs {Cavia), and the S. American capybara {Hydro- 

 chcerus), the largest living Rodent, measuring about 4 ft. in 

 length. 



4. I.agomorpha. — Hares and rabbits {Leptis), and the picas or 



tailless hares {I.agomys), with m.cisors -. 



In the first three sub-orders there is only a single pair of upper 

 incisors, and the three may be united as Simplicidentata, in contrast 

 with the Duplicidentata, where there are two pairs. Only in the latter 

 does the enamel extend to the posterior surface of the incisors, which 

 are alscf pecuhar (in this order) in having well-developed milk pre- 

 decessors. 



Order Carnivora 



This order includes lions and tigers, foxes and dogs, 

 bears and otters, etc. 



Most of the Carnivora feed on aniYnal food, and the most 

 typical forms prey upon other animals and devour their 

 warm flesh. Most are bold and fierce animals, with keen 

 senses and quick intelligence, and often much beauty of 

 form and marking. 



Almost all have well-developed claws ; there are never 

 fewer than four toes. The teeth are always rooted ; the 

 canines are strong and sharp ; some of the back teeth are 

 generally sharp, and specially adapted for cutting. 



