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. 



FIQ. 16. CEREBROSPINAL NERVOUS SYSTEM. 

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

 nerve; 5, pneum'ogastric nerve; 6, spinal cord; 10, radial nerve; 11, median 

 nerve; 12, pneumogastric nerve; 13, portion of solar plexus; 14, solar plexus; 

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

 lior plantar nerve; 22, internal radial nerve; 23, anterior plantar nerve; 24, 

 digital nerves. 



Divisions. — The brain is divided for study into: (a) cere- 

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



The cerebri/ in 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 cerebellum , smaller than the cerebrum, is located in the 

 posterior and inferior part of the brain cavity, and consists of 

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



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