DISEASES OF HORSES 381 



cerebellum cause disturbances of the equilibrium, but do not inter- 

 fere 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 flat- 

 tened 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 activ- 

 ity 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 back- 

 bone, 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 cquinas. A transverse section of 

 the cord reveals that it is composed of white matter externally and 

 of gray matter internally. The spinal oord 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 distrib- 

 uted, viz : 



1. Olfactory. 



2. Optio. 



3. Oculo-motor. 



4. Pathetic. 



5. Trifacial. 



6. Abducens. 



7. Facial. 



8. Auditory. 



9. Glosso-pharyngeal. 



10. Pneumogastric. 



11. Spinal-accessory. 



12. Hypoglossal. 



INFLAMMATION OP 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, ex- 

 cept in direct mechanical injuries to the head or diseases of the 

 bones of the cranium. Neither is the arachnoid often affected with 



