150 MAN, THE ANIMAL 



system is closely organized and specialized Into 

 a brain and spinal cord. Here are found the 

 same motor cells connected with the muscles and 

 veins of the body and numerous nerve cells that 

 serve to connect the different parts of the central 

 nervous system. This latter class of cells is al- 

 ways located entirely within the central nervous 

 system. Part of the sensory nerve cells of verte- 

 brates remain on the surface of the body as the 



Figure 50. Diagram of the brain of a dogfish. The "nose 

 brain" is shown with small dots; the "eye brain" in coarse dots 

 and the "ear brain" in solid black. 



eyes, taste, smell and hearing; and part of them 

 have taken up a position deep within the body, but 

 they send nerve fibers to the surface as in touch, 

 cold or hot receptors. There are also special 

 nerves which carry sensory stimuli from the in- 

 ternal organs, such as hunger or pain when the 

 source is internal. 



In the fishes the brain is largely an enlargement 

 of special sense centers. The anterior end is 

 given over to olfaction, a large part of the mid- 



