290 VERTEBRATA 



spinal cord and brain form the central nervous system 

 which the microscope shows to be composed of millions 

 of cells with processes varying in length from a hundredth 

 of an inch to nearty a foot. The longer processes are 

 called fibers, and many of them bound together form a 

 nerve such as is most distinctly seen in the limbs. 



The brain of mammals is composed of five parts: the 

 medulla oblongata, the cerebellum, the cerebrum visible 

 from above, and the rn'id brain and interbrain lying beneath 

 the cerebrum. The intelligence of an animal seems to 

 depend largely on the size and structure of the cerebrum. 

 In the lower mammals the surface is quite smooth, while 

 in the rabbit and cat it is somewhat convoluted, and in ape 

 and man the convolutions become very numerous. The 

 average weight of the male human brain is about three 

 pounds; of a female about two and two thirds pounds. 

 The human brain is one forty-fourth the weight of the body ; 

 the ape's one twenty-ninth; the rat's one eighty-second; 

 the sheep's one three hundred and fifty-first, and the ele- 

 phant's one five-hundredth. The brain of man is larger 

 than that of any other animal except the whale and ele- 

 phant. The brain of a large whale weighs over four pounds, 

 while that of a large elephant will weigh about ten pounds. 



The skeleton of the cat consists of more than two hundred 

 bones united to each other by tough bands of tissue called 

 ligaments. The three parts of the skeleton are the head, 

 trunk, and extremities. Except the lower jaw, the bones 

 of the head are immovably united to each other. The 

 bones of the trunk are capable of only limited motion, but 

 free movement occurs between several of the limb bones. 

 A typical mammalian fore limb consists of a shoulder blade 



