6 FAMILY ODOB^NHXE. 



more anteriorly. Accordingly, in respect to general form, we 

 have slenderness of both body and limbs in the one contrasted 

 with great thickness of body, and distally a disproportionate 

 reduction of the extremities in the other. The most striking- 

 differences, however, exist in the cranial characters, resulting 

 from the great development of the upper canines in the Wal- 

 ruses, and the consequent modifications of the facial portion of 

 the skull. In the Otariidce, the general contour of the skull is 

 strongly Ursine ; in the Odobcenidce, it is unique, owing to its 

 great expansion anteriorly. In respect to other cranial features, 

 the Walruses differ from the Eared Seals in having no post-orb- 

 ital processes, and in the mastoid processes being not separated 

 from the auditory bullae. The teeth are all single-rooted, and 

 have in the permanent dentition no distinct crowns. 



On comparing the Odobccnidw with the Phocida', the differ- 

 ences in general structure are found to be far greater than ob- 

 tain between the Walruses and Eared Seals, especially in regard 

 to the himl extremities ; these in the Phocida' being directed 

 backward, and useless as organs of terrestrial locomotion. 

 Hence, in so far as the Odobanida' and Otariidcc agree in liinb- 

 aud skull-structure, they both similarly depart from the Phocine 

 type. As already indicated in the synopsis of the suborder Pin- 

 nipcdia, the Phocida' differ far more from either the Odobcenidw 

 and Ota>-iida> than do these latter from each other. This differ- 

 ence is especially emphasized in the skull ; for while the Odo- 

 bwnida' and Otariida' agree in all important cranial characters, 

 aside from the special features correlated with the immense 

 enlargement of the upper canines in the former, they widely 

 differ from the Phocida'. This is especially seen in the absence 

 in the latter of an alisphenoid canal, in the greatly swollen audi- 

 tory bulla?, the position of the carotid foramen, and the non- 

 salient character of the mastoid processes. 



The few points in which the Walruses differ in myology from 

 other Pinnipeds, Dr. Murie states to be "the presence of a co- 

 raco-brachialis, a flexor brevis nianus, a pronator quadratus, an 

 opponens pollicis, and a palmaris brevis," in the possession of 

 which it differs both from Otaria and Phoca, but that in other 

 respects they " muscularly present general agreement." " Com- 

 pared with the Seals \Plioca ] there are two extra peronei and 

 a flexor brevis hallucis." 1 " Though deficient in concha, the auri- 

 cular muscles are remarkably large."* 



:r Proc. Zool. Soc. Lond., 1870, p. 545. 



