THE NERVOUS SYSTEM. 



229 



FIG. 114. BRAIN OF THE 

 RABBIT FROM DORSAL 

 ASPECT. 



c, cerebellum. Three 

 fifths natural size. 



striking similarity to the brains of 

 reptiles and birds. The brains of 

 Rodentia possess but few convo- 

 lutions, while the brain of man is 

 the most highly convoluted. 



The size of the brain varies 

 widely. As a rule, the larger the 

 brain in proportion to the size of the 

 animal, the greater is its intelligence. 

 However, in man this statement 

 does not always hold true, as an indi- 

 vidual with a small brain may be 

 much more capable mentally than 

 one with a large brain. Mental 

 power in man seems to depend upon 

 the development of the cells and 

 fibers of the brain. 



The average weight of a male human brain is about three 

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

 The human brain is -^ the weight of the body; the ape's, 

 2*9; the rat's, ^; the sheep's, g| T ; and the elephant's, -g^- . 

 The brain of man is larger than that of any other mammal 

 except the whale and elephant. The brain of a large whale 

 weighs over four pounds, while that of a large elephant 

 will weigh about ten pounds. 



PRACTICAL QUESTIONS AND SUGGESTIONS. 



1. How many nerves transmit the stimuli received by the organs of 

 special sense? 



2. Where are the sense organs of pain located? 



3. How many sense organs are visible in the mesentery of your 

 specimen? 



4. Describe the path of a stimulus from the index finger to the brain. 



5. Through which nerve roots would the stimuli received by the 

 cutaneous sense organs pass into the cord? 



6. Describe the nerves transmitting the stimuli from the olfactory 

 organ. 



