THE NERVOUS SYSTEM. 



623 



cells, granular or fibrillated, with large and distinct nuclei, arranged 

 with their apices toward the surface. 



Chemical Composition. The chemistry of nerves and nerve-cells has 

 been chiefly studied in the brain and spinal cord. Nerve matter con- 

 tains several albuminous and fatty bodies (cerebrin, lecithin, and some 

 others), also fat matter which can be extracted by ether (including cho- 

 lesterin) and various salts, especially Potassium and Magnesium phos- 

 phates, which exist in larger quantity than those of Sodium and Calcium. 



Arrangement of the parts of the cerebrum. The great relative and 

 absolute size of the Cerebral hemispheres in the adult man, masks to a 



Fig. 375. Diagrammatic horizontal section of a vertebrate brain. The figures serve both 

 for this and the next diagram. Mb, mid-brain : what lies in front of this is the fore-, and what 

 lies behind, the hind-brain ; Lt, lamina terminalis ; Olf, olfactory lobes ; Hmp, hemispheres ; 

 Th. E, thalamencephalon ; Pn, pineal gland; Py, pituitary body; F.M* foramen of Munro; cs, 

 corpus striatum ; Th, optic thalamus ; CC, crura cerebri : the mass lying above the canal rep- 

 resents the corpora quadrigemina ; Cb, cerebellum; I IX, the nine pairs of cranial nerves; 1, 

 olfactory ventricle ; 2, lateral ventricle ; 3, third ventricle ; 4, fourth ventricle ; +, iter a tertio 

 ad quartum ventriculum. CHuxley.) 



great extent the real arrangement of the several parts of the brain, which 

 is illustrated in the two accompanying diagrams (figs. 375, 376). 



From these it is apparent that the parts of the brain are disposed in 

 a linear series, as follows (from before backward) : olfactory lobes, cere- 



