436 THE ANATOMY OF VEKTEBRATED ANIMALS. 



in the cai-pus intercalated between the proximal and the 

 distal series. The digits are five, ungulate, and provided 

 with small claws. 



There is a bone in the penis. The testes do not leave the 

 abdomen, but come down into the gi-oin in the breeding 

 season. Yesiculse seminales and prostatic glands are 

 present. In the female the uterus is, in many genera, 

 completely divided into two cornua, each of which opens 

 separately into the vagina; bxit, in the rest, the comua 

 unite into a corpus uteri. 



Some genera depart widely from the rest in particular 

 points; for example, in the Porcupines, the haii's on the 

 dorsal region of the body are very much enlarged, acquire 

 a peculiar structvire, and form the so-called " quills." Some 

 of the Porcupines have prehensile tails. 



In Cavia and Hydrochcerus the toes are reduced to three, 

 and the nails have almost put on the character of hoofs. 



The Squirrels have the short pollex almost opposable. 



The femui" in some Rodents has a well-developed third 

 trochanter ; and in Dipus, the Jerboa, the long metatarsals 

 become ankylosed together into a cannon bone. 



In the Porcupines, the suborbital foramen is enormous, 

 and an anterior fasciculus of the masseter muscle arises 

 from the maxilla, and traverses the foramen to its insertion. 



The Hamster (Cricetus) has great cheek pouches, pro- 

 vided with special retractor muscles connected with the 

 spines of two lumbar vertebrae. 



In some genera, the stomach, which is iisuaUy simple, 

 tends to become complex. Thus the cardiac division of 

 the stomach of the Beaver is provided with a special glan- 

 dular mass. The cardiac end of the oesophagus of the 

 Dormouse is glandular and dilated like the proventiculus 

 of a bird. And, in Arvicola, the stomach becomes deeply 

 consti'icted, and a groove leads from the oesophagus towards 

 the pyloric end, reminding one of certain Artiodadyla. 



In some few genera, the ureters open into the fundus of 

 the bladder, or near it. 



Although the genera and species of the Ecdentia are 



