THE EXTERNAL FORM OF WHALES 27 



deal with one or two other points in the structure of 

 the hind limb. In Balanoptera muscuhis the rudimen- 

 tary femur is attached to the pelvis by two ligaments, 

 one anterior, and the other posterior. In these liga- 

 ments rudiments of muscle appear in the shape of 

 a few fibres. The actual correspondence of these 

 muscles with those of terrestrial mammals depends 

 of course on what view is taken of the homologies 

 of the ischium. If the pelvis is simply an ischium, 

 then the arrangement of the bands of ligament would 

 seem to show that of all femur left is the great 

 trochanter, a process of that bone particularly well 

 developed in many mammals. In Balcena mysticetus 

 there are three recognisable slips of muscle.* 



HAIR 



One of the most universal definitions of the 

 mammalia is the possession of a hairy covering. 

 No other animals have any epidermal structures 

 which are strictly comparable to hairs ; and hairs 

 are present in almost all mammals. The whales 

 indeed are the only exception to the universality 

 of this statement, and they are, after all, only a 

 partial exception. The White whale, Beluga, and 

 the Narwhal, Monodon, appear never to possess 

 any hairs, either as adults or foetuses. But in many 

 other species hairs have been found to persist in 

 the adult condition sometimes in diminished numbers ; 



* STRUTHERS, " Rudimentary Hind Limb of a Great Finwbale," Jour. 

 Anat. P/iys., xxvii., p. 291. 



