192 DISEASES OF THE HOKSE. 



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

 cerebellum is composed of gray matter externally and of white matter 

 in the center. The cerebellum has the function of coordinating move- 

 ments ; that is, of so associating them as to cause them to accomplish a 

 definite purpose. Injuries to the cerebellum cause disturbances of ths 

 equilibrium, but do not interfere with the will power or intelligence. 



The cerebrurri'^ or brain proper, occupies the anterior portion of the 

 cranial cavity. It is ovoid in shape, with an irregular flattened base, 

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

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

 cerebrum are usually said to be the seat of all psychical activities. 

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

 willing possibk. After thej^ 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 spinal cord^ or spinal marrow, is that part 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 

 lateral symmetrical halves by fissures. The sj^inal cord terminates 

 posteriorly in a pointed extremity, which is continued by a mass of 

 nerve trunks — candci equiiuK. A transverse section of the cord reveals 

 that it is composed of white matter externally and of gray matter 

 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 spinal nerves, forty-two or forty-three in number, arise each 

 by two roots, a superior, or sensory, and an inferior, or motor. The 

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

 arranged in pairs, 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-pharyugeal. 



4. Pathetic. 10. Pneumogastric. 



5. Trifacial. 11. Spinal-accessory. 



6. Abducens. 12. Hypoglossal. 



INFLAMMATION OF THE BRAIN AND ITS MEMBRANES. 



Inflammation may attack these membranes singly, or any one of the 

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

 at once. Practical experience, however, teaches us that primary 

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

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



