SKELETONS OF THE SEAL AND WALRUS. 161 



lower one in breadth. The spine terminates by a short 

 and simple acromion. The humerus is short and thick, 

 and is remarkable for the great development of the inner 

 tuberosity and of the deltoid ridge, which is deeply ex- 

 cavated on its outer side. The inner condyle is per- 

 forated. The scaphoid and lunar bones are connate. 

 Although the pollex or the first digit exceeds the third, 

 fourth, and fifth in length, it presents its characteristic 

 inferior number of phalanges, by which the front border 

 of the fin is rendered more resisting. The pelvic arch is 

 remarkable for the stunted development of the ilia, and. 

 the great length of the ischia and pubes. The femur is 

 equally peculiar for its shortaess and breadth. The tibia 

 and fibula present the more usual proportions, and are 

 anchylosed at their proximal ends. The bones of the 

 foot are strong, long, and are modified to form the basis 

 of a large and powerful fin: the middle toe is the shortest, 

 and the rest increase in length to the margins of the foot ; 

 the inner toe has, nevertheless, but two phalanges, the 

 rest having three phalanges, whatever their length; and 

 this is the typical character, both as to the number of the 

 digits and their joints, in both fore and hind feet of the 

 mammalia. 



In the living walrus and seal, the digits of each ex- 

 tremity are not only bound together by a common broad 

 web of skin, but those of the hind-limbs are closely con- 

 nected with the short tail: being stretched out back- 

 wards, they seem to form with it one great horizontal 

 caudal fin, and they constitute the chief locomotive organ 

 when the animal is swimming rapidly in the open sea. 

 The long bones of seals, like those of whales, are solid. 



With regard to the skull in the seal-tribe, it may be 

 remarked that an occipitosphenoidal bone is formed, as 



14-^ 



