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

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

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

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

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

 willing 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 inte- 

 gration of movements. Injuries to the cerebellum cause disturbance of 

 the equilibrium of the body, but do not interfere with the psychical 

 activities or the will or consciousness, neither does an injury to these 

 parts give rise to pain. 



The spincd 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 spinal cord terminates 

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

 vous trunks — cauda equincc. A transverse section of the cord reveals 

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

 The spinal cord does not fill up the whole spinal canal. The latter con- 

 tains, 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 func- 

 tions, or the parts to which they are distributed, viz : 



1. Olfactory. 



2. Optic. 



3. Oculo-motor. 



4. Putlietic. 



7. Facial. 



8. Auditory, 



9. Glosso-Pharyngeal. 



10. Pneumogastric. 



11. Spinal-Accessory. 



12. Hypoglossal. 



6. Abdaeens. 



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 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 cranium. 

 Neither is the arachnoid often affected with acute inflammation except 

 as a secondary result. The pia mater is most commonly the seat of 

 inflammation, acute and subacute, but from its intimate relation with 

 the surface of the brain the latter very soon becomes involved in the 



