VERTEBRATA MAMMALIA. 



31 



28. Respiration. The thorax or chest is separated 

 from the abdomen by a muscular partition called the 

 diaphragm, which plays an important part in the work of 

 respiration. In the abdomen are 



placed the greater part of the 

 alimentary canal, the stomach, 

 the liver, kidneys, &c. The heart 

 and lungs are situated in the 

 thorax. There are two lungs, 

 which are spongy and elastic, and 

 abound in air cells. They are 

 freely suspended in the cavity of 

 the thorax, and each of them is a __ 

 enclosed in a membranous sac 

 called the pleura (Or. pleura, 

 the side). Their bronchi, or 

 branches of the windpipe which 

 traverse them, never communi- 

 cate with air sacs in the body, as 

 those of birds do. 



29. Nervous System. The 

 brain in the Mammalia is much 

 larger than in the other verte- 



brates. The two hemispheres of vena cava; & right auri- 



, . y , cle ; c, right ventricle ; d, pul- 



the Cerebrum, Or principal maSS monary artery ; e, pulmonary 



of the brain, are united by a ^^i^SSMff. 



band of nerve fibres termed the laries of the lungs; i 1 , capii- 

 corpus callosum (Lat. "the firm SS^^SSSu Theven ~ 

 body"). 



30. Sight and Hearing. All mammals possess eyes, but 

 in some instances the sight is very imperfect. Except 

 the whales, and some of the seals, all have an external 

 ear. 



31. Covering. The covering consists of hair, which is 

 only found in this class. Hair is of the same nature as 

 feathers, but does not split up as feathers do. It is 

 always developed by some part of the skin, except in 

 the whales and the scaly ant-eater. In the hedgehog 



Fm 8 ._ CmcuLATION OF A 

 MAMMAL. 



