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 cerebellum 
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 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 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 equine. 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 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. Auditory. 
38. Oculo-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 with acute inflamma- 
tion, except as a secondary result. The pia mater is most commonly 
