192 BUREAU OF ANIMAL INDUSTRY. 



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

 cranial cavity. It is ovoid in shape, with an irreguhir 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 ps^'chical activities. 

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

 willing possible. After they are destroj^ed, the organism comes to be 

 like a complicated machine, and its activity is onl}' the expression of 

 the internal and external stimuli which act upon it. 



The .y)in(fl eoyd, or spinal marrow^, is that part of the cerebro-spinal 

 SA'stem which is contained in the spinal canal of the l)ackbone, 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 tissures. The spinal cord terminates 

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

 nerve trunks— «/*^<:Z« equina'. A transverse section of the cord reveals 

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

 nally. The spinal cord does not fill up the whole spinal canal. The 

 latter contains, besides, a large venous sinus, fatt}' matter, the mem- 

 branes of the cord, and the cerebro-spinal fluid. 



The spinal nerves, forty -two or forty-three in number, arise each l)}^ 

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

 nerves originating from the brain arc twent3'-four in number, and 

 arranged in pairs, which arc 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-pharyngcal. 



4. Pathetic. 10. Pneumogastric. 



5. Trifacial. 11. Si)inal-accessory. 



6. Abducenp. 12. Ilypogloggal. 



INFLAMMATION OF THE BRAIN AND ITS MEMBRANES. 



Inflammation ma}' 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 cranium. 

 Neither is the arachnoid often affected with acute inflaumiation, except 

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

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

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

 morbid changes. Practically, we can not separate inflammation of the 



