PINNIPEDIA. 625 



which they differ mainly in their dentition, aquatic habits 

 and the structure of their limbs. The limbs are short and penta- 

 dactyle, the proximal jDortions being more or less imbedded 

 in the common integument of the body. All the digits are 

 united by a membrane which may or may not project beyond 

 their extremities. Nails are occasionally well developed^ but 

 generally small or even absent. They are all covered with 

 hair, and there is sometimes a fine soft under-fur, which in the 

 fur seal is much developed. The incisors vary in number 

 and are conical ; they are never less than 4- The canines 

 jDroject though not as much * as in the Carnivora. The 

 premolars and molars are all alike, and may be conical and 

 one-rooted, or laterally compressed with three cusps and two 

 roots ; their number varies from five to six. The milk teeth 

 are i f, c y, m ^ and are shed early, either before or shortly 

 after birth. The cranium is generally rounded and capacious. 

 The orbits are open behind and there is no lacrymal bone or 

 canal. The tympanic bulla is large and is prolonged beneath 

 the meatus auditorius ; the paroccipital and mastoid processes 

 are inconspicuous. The condylar foramen is distinct from 

 the foramen lacerum posterius, and an alisphenoid canal is 

 present or absent. The mandible has a coronoid process. 

 The tail is short. Clavicles are absent ; the scapula is 

 large, the spine being nearer the hinder edge. The humerus 

 is short and without entepicondylar foramen. Ulna and 

 radius are separate, and the scaphoid and lunar are fused. 

 The calcaneum has a short tuber calcis. There is always a 

 considerable os penis. The brain is large and well convoluted, 

 the olfactory nerves and anterior commissure small. The 

 colon has a short caecum. The kidneys are lobulated, and 

 Cowper's glands are absent. The mammae, two or four in 

 number, are abdominal. A scrotum may be present or absent. 



They are all aquatic, but come to the land, on which they 

 move clumsily, to breed. They are mainly marine, but some 

 species ascend rivers, or inhabit inland seas and lakes. Their 

 fossil remains are found in Europe and North America from 

 the Miocene onwards. 



There can be no doubt that the Pinnipedia are allied to 



* Except in the walrus. 

 Z-ll s s 



