AQUATIC MAMMALS 



scrotal. The canines are enormously and phenomenally enlarged, 

 especially in males. The greater tuberosity of the humerus is higher 

 than the lesser. The ilium is moderately curved ourward, to a greater 

 extent than in the otariids and less than in phocids, and the femur is 

 without a lesser trochanter. 



Phocidae 



These are the true seals or earless seals, of which there are numer- 

 ous genera, are found locally almost throughout the world, even in 

 some large lakes. The pelage is hairy and never with a furry under- 

 coat, but the pelage of the young, at least in a number of genera, is 

 long and woolly, this being shed either shortly after birth or m utero. 

 The area of the fore foot is reduced, the axilla falls opposite the wrist, 

 and in most sorts these members are of use only for equilibration, on 

 land being employed only for surmounting obstacles; although in the 

 elephant seal {Mboiinga) at least, they are usually placed fairly flat 

 upon the ground. The area of the hind foot is somewhat increased, 

 relative to length of limb, these appendages being plainly indicated 

 as the means for aquatic propulsion, which is accomplished by rhyth- 

 mic lateral movements as by the tail of most fishes. In spite of the 

 apparent inefficiency of terrestrial locomotion, which is accomplished 

 by a caterpillar-like wriggling of the body, with the hind feet elevated, 

 seals have been known to travel overland for many miles, and even 

 through mountainous country, when the freezing of coastal waters 

 has made it advisable for them to seek new aquatic territory. 



The astragalus has a posterior projection as long as that of the cal- 

 caneum and the foot is prevented from assuming a plantigrade posture 

 by the unusual tension of the flexor hallucis longus tendon. There 

 are no cartilaginous prolongations of the digits and the palm and sole 

 are as well haired as the dorsum of the feet. The nails are all well 

 formed, except that they are absent from the pedes of M'nounga. The 

 testes are abdominal. The canines are but moderately developed. The 

 vertebral spines of the anterior thorax are poorly developed. The lesser 

 tuberosity of the humerus is usually higher than the greater, the ilium is 

 markedly and abruptly bent outward, and there is no femoral lesser 

 trochanter. 



I have already discussed the pinnipeds at considerable length 

 (Howell, 1929). Their derivation is a matter of controversy, for al- 

 though both otariids and phocids are known from the Tertiary, they 

 were even then true pinnipeds. It is a commonly accepted belief that 



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