432 DISEASES OF THE BRAIN 



disturbances as well as impaired mobility and sensation on 

 the opposite side of the body, the degree of impairment 

 depending upon the extent of the lesion. 



The Midbrain (Crura Cerebri, Corpora Quadrigemini and 

 Optic Thalami).This portion of the brain is the seat of 

 harmony of motion and equilibrium. ' As some of the cranial 

 nerves arise here, the fifth pair being the most important 

 of these, any disease, destructive process or undue pressure 

 operating on this part of the brain will produce sensory 

 and motor disturbances in the region of the face, lips, eyes, 

 ears and part of the tongue, and, if extensive, the entire 

 organism may be affected. Involuntary movements of the 

 limbs, head, neck and eyes are the most common symptoms 

 resulting. 



The Cerebellum. The functions of the cerebellum or hind- 

 brain are not fully known but it is regarded as being closely 

 connected with locomotion and equilibrium. It is also 

 thought to be the seat of the muscle sense and assists in the 

 coordination of the muscle movements. Each hemisphere 

 of the cerebellum presides over the muscles of the same side 

 of the body and if either half be injured or diseased the 

 animal will exhibit muscular and motor disturbances of 

 the same side, varying in degree from slight muscular 

 incoordination to spasmodic movements, or it may walk 

 in a circle or crowd or roll toward the injured hemisphere. 



Examination. The brain, because of its position, pro- 

 tected by the bones of the cranium, cannot be examined 

 directly. Diseases of this organ can be recognized only 

 by observing the disturbed functions produced after patho- 

 logical changes have occurred. It is necessary, therefore, 

 to examine carefully the functions of the brain before one 

 can arrive at definite conclusions. 



As the brain is the seat of the mind (thought), feeling, 

 consciousness, sensibility and voluntary movement, any dis- 

 turbances or impairment of these functions must be 

 attributed to some pathological change in that organ. 



Taking up the examination of the brain by examining its 

 functions in the order named above, the psychic function or 

 mental condition will be first considered. 



