ART. 15 ANATOMY OF THE EARED AND EARLESS SEALS HOWELL 9 



urements and percentages are also presented of the skeleton of an 

 adult cat {Felis catus). 



Some vertebral measurement was needed as a standard of com- 

 l^arison but it was thought advisable to exclude from this the cervical 

 series. The sum of the length of the thoracic, lumbar and sacral 

 vertebrae has therefore been taken as a yardstick. It was found 

 that this measurement in the Phoca skeleton was almost precisely 

 seven-tenths that of the Zalophus. In drawings of single bones of 

 the latter the scale is, therefore, as though the osteological details 

 of this individual were precisely seven-tenths of their true size. At- 

 tention should be called to the fact that classification of the osteo- 

 logical characters as being of myological or phylogenetic derivation is 

 at times arbitrary and purely for convenience. Any character doubt- 

 less become phylogenetic if present for a sufficient length of time. 

 By " transverse process " is meant any ■ vertebral process situated 

 laterad without reference to its homology, as of the atlas or of a 

 sacral vertebra. 



The illustrations give a better idea of the general form of the skull 

 than can a description. That of the Zaloflius is long and narrow, 

 and in the Phoca short and broad, most of the difference in length oc- 

 curring anteriorly. In the Zaiophus the skull is 27 and in the Phoca 

 23 per cent of the body length. In the same order the glenoid-rostral 

 measurement is respectively 70 and 61 per cent of the total length of 

 the skull, and that for breadth to length is 53 and 66 per cent 

 respectively. Beginning rostrad it is seen that there has been a 

 slightly greater recession caudad of the anterior nares, relative to 

 total length of skull, in the Phoca. In the Zalophus there is a Avell 

 defined process formed by the premaxillary tips, which is absent in 

 the Phoca. The reason for this is apparently either muscular or 

 possibly cartilagenous, but nothing to account for it was met during 

 dissection. Similarly the anteorbital processes of the maxillae, pres- 

 ent in Zaloyhus only, should be due chiefly to details of the orbicu- 

 laris oculi, and possibly also the frontalis, but as mentioned later I 

 am not reporting upon the facial musculature. The absence of supra- 

 orbital processes in the Phoca and their presence in Zalophus is cor- 

 related first with the lack in the former of a distinct " interorbital " 

 extension of the temporalis, with the greater size in that animal of 

 the eyes and the true orbits (as distinguished from the anterior 

 temporal fossae), and their more dorsal position, or rather, the more 

 pronounced ability of the eye to look straight up. This more dorsal 

 direction of sight can be accomplished in two ways — {a) by a bowing 

 out and broadening of the zygomatic arches, accompanying which 

 change there must be either a decided increase in the strength of the 



