NERVOUS SYSTEM. 



73 



When we study the skeleton we shall recur to the description 

 of these parts. 



13. The brain, or cerebrum 

 (Fig. 25, c.) is a voluminous 

 viscus, of a very soft texture, 

 and of an oval form, whiA 

 fills the greatest part of the 

 anterior of the cranium. It 

 is divided on a middle line, 

 by a very deep furrow, into 

 two halves called liemisphms 

 iff the. brain. Each of these 

 hemispheres is subdivided, in 

 its turn, into three lobes, and 

 presents on its surface a great 

 number of hollows and projec- 

 tions, folded on themselves, 

 called the convolutions of ike 

 brain. We find in the inte- 

 rior, cavities called ventricles, 

 and we distinguish in the sub- 

 stance of which it is composed, 

 two sorts of matter, one white, 

 called medullary, which occu- 

 pies the interior of the mass of 

 the brain, and the other, of a 

 greyish colour, forms its super- 

 ficies, and is called cortical. 



14. Behind and below the 

 cerebrum, or brain, we find, 

 also in the cavity of the 

 cranium, another nervous 

 mass, very much smaller, but 

 of analogous structure, which 

 is called the cerebellum. (Fig. 

 25, en.) 



Fig. 25. 



ps 



Explanation of Fig 25. The nervous system. c. the cerebrum. cv. the 

 cerebellum. we. the spinal marrow from which arises a great many nerves 

 which ramify over all parts of the body. pb. the biachial plexus or reunion 

 or assemblage of the different nerves which are distributed to t'.ie arms. ps. 

 ^the sciatic plexus or assemblage of nerves which form the great sciatic 

 i.erve which descends to the lower extremities. 



13. What is the brain ? ITow is it divided ? What are ventricles ? Wha! 

 is the difference between the medullary and cortical parts of the brain ? 



14. What does the cranium contain besides the cerebrum ? 



