The Nervous System. 281 



in the horse. They are considered to be the centres for 

 co-ordination of motor impulses ; when they are destroyed 

 the animal has an irresistible tendency to move forwards. 



I have certainly seen this latter symptom shown in the 

 horse in disease of the corpora striata, but it is far from 

 invariable. It is remarkable how extensively the parts may 

 be affected and pressed upon by tumours without symptoms 

 being exhibited ; the gradual pressure or destruction may 

 account for this. 



Cerebellum. 



In the cerebellum is found a collection of fibres and 

 ganglion cells, in direct communication with the medulla 

 and cerebrum. It is the first piece of nervous tissue we 

 have studied where the surface has been folded and doubled 

 in on itself to a considerable extent, forming the so-called 

 convolutions ; it is composed of grey and white matter, the 

 grey being externally placed and not internally as in the 

 cord. 



The functions of the cerebellum are principally concerned 

 in the co-ordination of movement, viz., harmony and rhythm 

 in muscular actions. It is enabled to carry out this function 

 through its connection with the superior columns of the 

 cord, which keep the cerebellum informed of the position of 

 the limbs. There can be no doubt that in co-ordinating 

 muscular movement, the cerebellum is assisted both by the 

 sense of sight, and by the lymph in the semicircular canals 

 of the ear. An animal walks with uncertainty when the 

 eyes are covered up, and disease of the internal ear is a 

 well-known cause of vertigo in the human subject. 



The cerebellum possesses no sensation ; it is essentially a 

 motor apparatus. When sliced away in birds they lose the 

 power of flying, walking, or preserving their equilibrium ; 

 there is no loss of consciousness or intelligence, but an 

 inability to co-ordinate the skeletal muscles. Injury to 

 one of the crura of the cerebellum produces what is termed 

 ' forced movements '; the animal rolls over and over around 

 the long axis of the body, and always from that side on 



