AHT. 15 ANATOMY OF THE EARED AND EARLESS SEALS HOWELL 133 



The proximal ends of the metatarsal bones in both animals seem to 

 have been subjected to transverse pressure, indicating that this part of 

 the foot may be narrower than in the ancestral forms. In Zalo'phus 

 this has resulted in making the metatarsal bases narrower and 

 deeper, but in Phoca merely in excessive crowding, with numerous 

 short processes filling all available spaces. A stimulus for this sort 

 of interlocking tarso-metatarsal articulations has probably also been 

 furnished by the fact that the feet of this animal are useless upon 

 land. After removal of the integument it is found that the otariid 

 metatarsus 1 and 2 are bound closely together, while there is a slight 

 amount of transverse play between the others ; in the phocid, 1 with 

 2 and 4 with 5 are so bound, and these, as two units, may be slightly 

 moved transversely from 3. As in the usual land mammal, however, 

 transverse movement of the metatarsals during the spreading of the 

 digits is found to be really very slight. 



In both pinnipeds there has been a strengthening and lengthening 

 of the first and fifth digits and their metatarsals which is of decided 

 use in stiffening both borders of the pes while it is expanded and 

 being forced against the water, but this seems to have been carried 

 to a greater extreme in Zalophus than can now be of real use. There 

 is a suggestion of flattening of the phalanges, especially upon the 

 plantar aspect in Zalophus^ and to some extent in all its digits and 

 metatarsals. This is specialization in the expected direction for an 

 aquatic mammal. 



There is no especial provision, in the way of arrangement of pedal 

 tendons, for the spreading of the otariid foot and the muscles of the 

 foot proper appear to be quite weak. This is not surprising, but one 

 is mildly astonished to be unable to distinguish any special provision 

 in the phocid either, although the plantar muscles are rather strong. 

 From manipulating the pes, however, it seems that spreading the 

 digits does not in this animal consist of purely transverse impulses, 

 but that this action is slightly oblique and consists very largely of 

 extending the first digit and moderately flexing the fifth at the meta- 

 tarsal-phalangeal joint only. Thus interrelated action between cer- 

 tain of the flexor and extensor tendons of the digits would supply 

 the activating power for spreading the toes, but the conformation of 

 these tendons does not disclose their identity. 



CONCLUSIONS 



A discussion of pinniped relationship is of decided secondary im- 

 portance in the present paper, but it is felt that it is desirable to offer 

 some consideration of this question, as well as some weighing from a 

 phylogenetic viewpoint of the anatomical evidence encountered. The 

 order may be characterized as follows: 



