32 



ANATOMY. 



closely to the pia mater. (3) The pia mater is thin, delicate, 

 and fits closely to the brain substance — over the convolutions and 

 into the depressions. 



Gray matter, folded into convolutions covers the surface. 

 The interior is composed of white matter. 



Function. — The physiological function of the brain is to re- 

 ceive messages, consider information, and send out appropriate 

 impulses or orders to the proper organs. 



FIG. 16. CEREBRO-SPINAL NERVOUS SYSTEM. 

 1. Brain; 2, optic nerve; 3, superior maxillary nerve; 4, inferior maxillary 

 nerve; 5, pneumoga.stric nerve; 6, spinal cord; 10, radial ner\-e; 11, median 

 nerve; 12, pneiimoRastric nerve; 13, iiortion of solar plexus; 14, solar plexus; 

 17, sciatic trunk; 19, gneat sciatic nerve; 20, posterior tibial nerve; 21, poste- 

 rior plantar net\e; 22, internal radial nerve; 23, anterior plantar nerve; 24, 

 digital nerves. 



Dii'isioiis. — The brain is divided for study into: (a) cere- 

 brum; (b) cerebellum; (c) medulla; (d) isthmus. 



The cerebrum is largest, and located in the anterior and su- 

 perior part of the brain cavity, and is divided into two lobes or 

 hemispheres by the median fissure. 



The cerebeUnm, smaller than the cerebrum, is located in the 

 posterior .'uid inferior ])art of the brain cavity, and consists of 

 three small lobes. Section shows the arbor-vitae (tree of life) 



