212 DISEASES OF THE HORSE. 



ordinating movements: that is. of so associating them as to cause 

 them to accomplish a definite purpose. Injuries to the cerebelhim 

 cause disturbances of the equilibrium but do not interfere with the 

 will power or intelligence. 



The cerebrum, 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 hah^es 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 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 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 spinal cord terminates 

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

 nerve trunks — cauda equinse. A transverse section of the cord reveals 

 that it is composed of white matter externally and of gi'ay matter 

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

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

 membranes of the cord, and the cerebrospinal 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. Aiulitory. 



3. Ocnlo-motor. 9. Glossopharyngeal. 



4. Pathetic. 10. Pneumogastric. 

 .5. Trifacial. 11. Spinal accessory. 

 6. Abducens. 12. Hypoglossal. 



INFLAMMATION OF THE BRAIN AND ITS MEMBRANES (ENCEPHA- 

 LITIS, MENINGITIS, CEREBRITIS). 



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 cra- 

 nium. Neither is the arachnoid often affected Avith acute inflamma- 

 tion, except as a secondary result. The pia mater is most commonly 



