644 



MAMMALIA. 



corresponds to the size of the brain lodged within it. It, however, 

 presents one point of physiological in- Fig. 299. 



terest, serving to prove still more de- 

 monstratively, that the temporal bone is 

 merely an adjunct to, and not essentially 

 a constituent part of, the cranium ; for 

 here the petrous portion of the temporal 

 bone, wherein is lodged the organ of 

 hearing, is entirely detached from the 

 skull, to which it is only fastened by a 

 ligamentous connection. This remarkable 

 arrangement is no doubt intended to pre- 

 vent the stunning noises that would else 

 be conveyed from every side to the ear, 

 by cutting off all immediate communica- 

 tion between the auditory apparatus and 

 the osseous framework of the head. 



The cervical vertebrae, in conformity 

 with the shortness of the neck, are exceed- 

 ingly thin ; and some of them are not 

 unfrequently anchylosed into one piece. 



The thorax is composed in the ordinary 

 manner ; but the posterior ribs are only 

 fixed to the transverse processes of the 

 corresponding vertebras. Behind the tho- 

 rax the whole spine is flexible, its move- 

 ments being untrammeled by any pelvic 

 framework, or posterior extremity ; so that, 



as in fishes, the broadly expanded tail is 



the great agent in locomotion ; and, from 



the horizontal position of this mighty oar, 



it is better adapted to enable the animal 



to plunge headlong into the depth, and to 



rise again to the surface, with all expedi- 

 tion, than if it had been placed vertically, 



as it is in fishes. 



The only vestiges of a pelvis met with 



in the Whale are, the rudimentary ossa 



pubis represented in the figure. These are 



imbedded in the abdominal muscles, and 



serve to support the external organs of 



