38 MOEPHOLOGY OF THE VERTEBRATA. 



The thoracic cavity is separated from the abdominal by a 

 well-developed diaphragm (compare this with pigeon.) The heart 

 is four-chambered, as in all other mammals, and there are two 

 anterior venae cavse. The external jugular vein is very much 

 larger than the internal. 



Of the muscles, attention may be drawn to the plantaris. This 

 muscle is peculiar in being very large, and terminating in a 

 tendon almost as large as the tendo achillis, which runs over 

 the end of the os-calcis, being separated from the tendo achillis by 

 a synovial sac. In the sole of the foot it divides into four tendons, 

 which are perforated for the long flexor tendons of the digits. 

 We mention this muscle because it differs from that of all other 

 mammals in the aspect we have alluded to. 



BRAIN. 



The cerebral hemispheres do not cover the cerebellum, and 

 the fissure of Sylvius is rudimentary. The olfactory nerves are 

 immense. The corpus callosum is relatively small, and its 

 anterior end is but slightly bent downwards. There is only one 

 corpus mammillare, and in the corpora guadrigemina the nates 

 are larger than the testes. The corpora trapezoidea are well 

 developed. 



SKELETON. 



Seven cervical and nineteen dorso lumber vertebrae, twelve of 

 these being dorsal. 



The transverse processes of the atlas are much expanded, and 

 the axis has a prominent long antero-posterior neural spine ; 

 while all the remaining cervical vertebrae have short spines. 



The spinous and transverse processes of the dorsal vertebrae 

 are well developed, the latter and the most anterior transverse 

 processes being especially prominent. At the eighth a process, or 

 metapophysis, springing from the side of the body of the vertebrae 

 between the spinous and transverse processes, becomes developed ; 

 and in the following vertebras this increases in size, till ip the 

 lumbar region it becomes the length of the spinous process. It 

 iB short in the last lumber and obsolete in the sacrum, but is 

 discernable through the anterior caudal vertebrae. 

 • The transverse processes of the lumber vertebrae are exceed- 

 ingly long, and project downwards and forwards. The transverse 

 process: of the first lumber is bifurcated at its extremity. On 

 the ventral sides of the centra of the three most anterior lumbar 

 vertebrae strong median processes are developed, which look 

 downwards and forwards : — to these are attached the crura of the 



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