THE NERVOUS SYSTEM. 



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87 



into, we find it composed, 1st, of a grey pulpy substance, mostly 

 placed externally, and, 2dly, of a similar white substance, placed 

 internally. The same materials exist in the spinal marrow, but the 

 white matter is external, while the grey is internal. What is com- 

 monly called the brain, is divided into the cerebrum or proper brain 

 (Figs. 32, #, and 33, a), and the cerebellum or lesser brain (Figs. 

 32, 6, and 33 6), which presents in its interior the branched appear- 

 ance of a tree (arbor vitse), as may be observed in Fig. 32. Both 

 these parts are divided longitudinally into two halves or hemi- 

 spheres, and also transversely into lesser parts called lobes. 



In the interior of the brain there are several cavities called ven- 

 tricles, two of which are of considerable size. Into these cavities 



Fig. 33. Base of the Brain and Spinal Cord.* 



* View of the base of the brain, anterior part of the spinal marrow, and attached 

 nerves, a, Cerebrum; b, cerebellum; e, spinal marrow; /, medulla oblongata. 1, Ol- 

 factory nerves ; 2, optic nerves ; 3, 4, 5, 6, 3d, 4th, Wi, and 6tk nerves ; 7 portio dura 

 of the 7fh and auditory nerves ; 8, glossopharyngeal nerves and pneumogastric nerves ; 

 9, spinal accessory and hypoglossal nerves ; 10, suboccipital nerves ; m, cervical plexus 

 of nerves ; g, plexus of the nerves going to the arms ; I, dorsal nerves ; n, lumbar 

 nerves ; k, plexus of nerves going to the lower extremities. 



