THE NERVOUS SYSTEM. 



77 



the brain. At the base of the brain are also the exits 

 of the twelve cranial nerves. 



Upon entering the brain the arteries run a tortuous 

 course, the tortuosity breaking the force of the blood 



FIG. 27. Base of brain. (Leidy.) 1, 2, 3, cerebrum; 4 and 5, longitudinal 

 fissure; 6, fissure of Sylvius; 7, anterior perforated spaces; 8, infundibulum; 9, 

 corpora albicantia; 10, posterior perforated space; 11, crura cerebri; 12, pon8 

 Varolii; 13, junction of spinal cord and medulla oblongata; 14, anterior pyramid; 

 14 X , decussation of anterior pyramid; 15, olivary body; 16, restiform body; 17, 

 cerebellum; 19, crura cerebelli; 21, olfactory sulcus; 22, olfactory tract; 23, olfac- 

 tory bulbs; 24, optic commissure; 25, motor oculi nerve; 26, patheticus nerve; 

 27, trigeminus nerve; 28, abducens nerve; 29, facial nerve; 30, auditory nerve; 

 31, glossopharyngeal nerve; 32, pneumogastric nerve; 33, spinal accessory nerve; 

 34, hypoglossal nerve. 



stream in the small vessels where congestion would be 

 with difficulty relieved. The basilar artery, which is 

 formed by the juncture of the two vertebrals, divides 

 into the two posterior cerebrals, each of which joins one 



