MUSEUM OF COMPARATIVE ZOOLOGY. 



27 



and 16, Plate III). In the latter the acromion is developed almost as 

 much as in the terrestrial carnivores, the crests are high, and the expan- 

 sion of the blade very great. In Phoca the blade is small, expanded 

 about equally anteriorly and posteriorly, the crest moderate, and the 

 acromion process slightly developed. The greater tuberosity of the 

 humerus, though large, does not rise above the base of the head of the 

 humerus, whilst the lesser tuberosity rises as a sharp point to a greater 

 height than the head of the humerus. In Eumetopias and Callorhinus 

 these conditions are reversed, the lesser tuberosity being but slightly 

 developed, whilst the greater is excessively so, rising to a greater height 

 than the head of the humerus, aud extending downwards more than 

 half the length of this bone, — much farther than in Phoca. Differences 

 are also traceable in the form of the bones of the forearm, carpus, and 

 metacarpus. In respect to the digits of the hand, they differ less in size 

 and length in Phoca than they do in the Otariadce and in Posmarus. 



By far the most important differences, however, are found in the 

 posterior organs of locomotion, — the pelvis and the hind limbs. The 

 latter are relatively smaller in the Phocidce than in the Otariadce, and 

 are very differently constructed and adapted to widely different uses, as 

 indicated in the following comparison. 



In the Phocidce the hind limbs are In the Olariadoe the hind limbs are 

 extended backwards in a line parallel somewhat free, and when in a natural 

 with the body ; the legs are so en- position (on land) the feet are turned 

 closed within the integuments of the forward, and serve to raise the body 

 body that they have little or no mo- from the ground.* 

 tion, and the feet are movable only 

 in a relatively small degree, in an 

 obliquely lateral direction. 



* It may be added that the foot is also relatively longer, as compared with the length 

 of the leg, than in Phoca, as shown by the following table, whilst the differences in the 

 size of the outer toes as compared with the middle ones is also greater. 



