8 PEOCEEDINGS OF THE NATIONAL MUSEUM vol.73 



in Figure 24. The extended breadth of the hind foot at the nails was 

 133 mm., but the difference between the collapsed and extended width 

 was slight. Upon the first and jfifth digits there were little more than 

 nail pits, as in the case of the fore foot, but the nails of the middle 

 digits were long, slender, and almost straight. Unlike the case of the 

 fore foot, the digits of the pes in this genus are capable of con- 

 siderable flexure, even to the cartilages, and the latter may be fl.exed 

 out of the way of the nails, permitting the use of these in scratching. 

 The sole is naked, but is covered with hair in the phocid. In the 

 latter the first and fifth toes are relatively more robust than in the 

 otariid and possible abduction of these digits is much greater, partly 

 because of the more generous width of the interdigital membrane. 

 Thus the greatest width of the foot at the base of the nails was 190 

 mm. in this specimen. Whereas in the otariid the static posture 

 assumed by the hind feet in the water is usually somewhat trailing 

 and relaxed, in the phocid they are usually adpressed and, especially 

 on land, carried straight out behind and unsupported. All five digits 

 have exceedingly slender, almost straight nails. 



OSTEOLOGY 



It is intended here to present not a complete description of the 

 skeleton of two species of pinnipeds as such, but rather to compare 

 critically two skeletons which are considered to be representative 

 of the families Otariidae and Phocidae. Minor differences in the 

 interrelationship of the bones of the skull are not dwelt upon, but 

 rather is it intended to enumerate and attempt to evaluate those 

 differences which are belived to be functional, as well as the phylo- 

 genetic ones, to discover why and to what degree pinnipeds differ fi-om 

 fissipeds, and in just what manner otariids differ from phocids. The 

 osteology of the pinnipeds has been described by a number of others 

 but no one heretofore has investigated the mechanical and myological 

 reasons for their osetological details. 



It has been impossible in the present instance to accumulate 

 skeletons of all, or even satisfactor}^ material representing the ma- 

 jority of, pinnipeds, but comparisons of skulls have been made, 

 family characters as based upon cranial details have been checked 

 over, and where the characters of the otariid or phocid differ from 

 those common to their respective families, these are mentioned. 



Other than of juveniles but one skeleton of Phoca Mspida (No. 

 6297, Mus. Comp. ZooL, Cumberland Gulf, April, 1878, sex un- 

 recorded, by L. Kumlein) could be located, and this is compared with 

 one of a subadult male Zalopus calif omianus (No. 200847, U.S.N.M., 

 from National Zoological Park, December 19, 1915) which is nearer 

 the same age than any other at hand. For comparison certain meas- 



