189 



in shape, the transverse diameter being greatest. The body of the 

 cerebellum is composed of gray matter externally and white in the 

 center. 



The cerebrum, or brain projier, occupies the anterior jiortion of the 

 cranial cavit^^ It is ovoid in shape, Avith an irregular flattened base, 

 and consists of lateral halves or hemispheres. The greater part of 

 the cerebrum is composed of white matter. The hemisjiheres of the 

 cerebrum are usually said to be the seat of all psj'^chical activities. 

 Only when they are intact are the ijrocesses of feeling, thinking, and 

 A\alling possible. After they are destroyed, the organism comes to be 

 like a complicated machine, and its activity is only the expression of 

 the internal and external stimuli which act upon it. The cerebellum 

 is the great and important central organ for the finer co-ordination 

 and integration of movements. Injuries to the cerebellum cause dis- 

 turbance of the equililjrium of the body, but do not interfere with the 

 l)S3'chical activities or the will or consciousness, neither does an injury 

 to these parts give rise to pain. 



The spinal cord or spinal marrow is that j)art of the cerebro-spinal 

 system which is contained in the spinal canal of the backbone, and 

 extends from the medulla oblongata to a short distance behind the 

 loins. It is an irregularly cylindrical structure, divided into two lat- 

 eral symmetrical halves by fissures. The spinal cord terminates pos- 

 teriorly in a i)ointed extremit}^, which is continued hy a mass of 

 nervous trunks — ccmda equince. A transverse section of the cord 

 reveals that it is composed of white matter externally and of graj'^ 

 internally. The spinal cord does not fill up the whole spinal canal. 

 The latter contains, besides, a large venous sinus, fatty matter, the 

 membranes of the cord, and the cerebro-spinal fluid. 



The sijinal nerves, forty-two or forty-three in number, arise each 

 by tAvo roots, a suj)erior or sensorj^ and an inferior or motor. The 

 nerves originating from the brain are twenty-four in number, and 

 arranged in j)airs, which are named first, second, third, etc., counting 

 from before backward. They also receive special names, according 

 to their functions, or the parts to which they are distributed, viz : 



1. Olfactory. 7. Facial. 



2. Optic. 8. Auditory. 



3. Oculo-motor. 9. Glosso-Pharyngeal. 

 •1. Pathetic. 10. Pneiimogastric. 



5. Trifacial. 11. Spinal- Accessory. 



C. Abducens. 12. Hjq^jogiossal. 



INFLAMMATION OF THE BRAIN AND ITS MEMBRANES. 



Inflammation may attack these membranes singly, or any of the 

 anatomical divisions of the nerve matter, or it may invade the whole 

 at once. Practical experience, however, teaches us that primar}" in- 

 flammation of the dura mater is of rare occurrence, except in direct 

 mechanical injuries to the head or diseases of the bones of the 



