6 FAMILY ODOB^NID^. 



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

 liave slenderness of both body and limbs in tlie one contrasted 

 witli great tliickness 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 skidl. In the Otariidw, the general contour of the skull is 

 strongly Ursine ; in the Odohcmidcv, 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 buUfe. The teeth are all single-rooted, and 

 have in the permanent dentition no distinct crowns. 



On comparing the Odohamidw with the Fhocidcc, the differ- 

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

 tain between the Walruses and Eared Seals, especially in regard 

 to the hind extremities ; these in the Phockhv being directed 

 backward, and useless as organs of terrestrial locomotion.. 

 Hence, in so far as the Odohcvnidw and Otariidw agree in limb- 

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

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

 nipedia, the Phocidce differ far more from either the Odohaniidce 

 and Otariidw than do these latter from each other. This differ- 

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

 bwnida' and Otariidw 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 Phocidw. This is especially seen in the absence 

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

 tory bullie, the position of the carotid foramen, and the non- 

 salient character of the mastoid processes. 



The few points in which the Wakuses differ in myology from 

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

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

 opponeus 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." " C om- 

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

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

 cular muscles are remarkably large."* 



* Proc. Zool. Soc. Lond., 1870, p. 545. 



