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CHAPTER XIII. 

 DISSECTION OF THE BABBIT. 



THE rabbit may be taken as a type of the mammalia ; and 

 the following points should be noted as characteristic of the 

 great majority of the members of the group. 



The distinguishing features of the skeleton have been 

 noted in the preceding chapter. 



Externally, the body is covered with hair: the urino- 

 genital and anal apertures are distinct from each other : and 

 there are large external ears. 



As regards the viscera : Mammary glands are present, 

 opening to the exterior on teats placed on the ventral surface 

 of the body. The heart has four chambers : there is a single 

 aortic arch in the adult, formed from the fourth left arch of 

 the embryo : the blood is hot, and the red corpuscles non- 

 nucleated. There is a complete diaphragm ; and the lungs, 

 which are not attached to the ribs, are completely surrounded 

 by pleurae. The ureters open directly into the bladder. In 

 the brain there is a corpus callosum, connecting the hemi- 

 spheres ; and corpora quadrigemina in place of corpora 

 bigemina. The cochlea is coiled spirally. 



The ova are extremely small, and are retained within the 

 uterus during almost the whole of their development. The 

 embryo receives a constant supply of nutriment direct from 

 the mother by means of the placenta, a structure in which 

 the blood-vessels of the embryo and of the mother are brought 

 into very close relation, so that diffusion can readily take 

 place from one to the other. 



In the following account the several systems are described 



