8 VERTEBRATE ANIMALS. 



zz. Above the diaphragm, in the thorax, are the lungs^ 

 lu, lu. Between the lungs is the heart, h, partly covered 

 by fat and other things. Below the diaphragm is the 

 liver, le, le', the stomachy ma, and the spleen, mi. Hanging 

 down from the stomach is a sort of apron, ne, ne; if it 

 were lifted up we should find behind it the intestines and 

 the kidneys. 



13. The Dorsal Cavity (a, a', Fig. i) is found in the head 

 and neck as well as in the trunk of the body. If the back 

 or top of a man's head were cut away the upper end of 

 the dorsal cavity would be opened and we should find it 

 to be a large chamber having the brain, N', in it. In the 

 neck and trunk the dorsal cavity is a narrow tube con- 

 taining in its upper two-thirds the spinal cord, N. 



14. Man is a Vertebrate Animal. The presence of the 

 ventral and dorsal cavities with a hard partition between 

 them is a chief fact in the anatomy of the human body : 

 it shows that man is a vertebrate animal, that is to say, is 

 a back-boned animal, and belongs to the same great group 

 as fishes, reptiles, birds, and beasts. Worms, clams, and 

 insects are invertebrate animals, that is, have no back-bone. 



15. Man's Place among Vertebrates. We have seen 

 that man is a vertebrate, or back-boned animal. Though 

 all vertebrates are alike in the general plan of their 

 structure, there are such differences that zoologists di- 

 vide them into classes. The most important of these 



13. Where does the dorsal cavity lie 1 Name its contents and give 

 their position. 



14. Why is man a vertebrate animal? Name some other verte- 

 brates. How are vertebrates distinguished from invertebrates ? Give 

 examples of invertebrate animals. 



15. Why are vertebrates divided into clashes? To which class 

 does man belong? Name some other mammalia. How do mamma- 

 lia differ from other vertebrates ? 



