CHOREA. 315 



Sometimes, however, it is of a reflex character, being due 

 to peripheral irritation, as, for example, when a bone spavin 

 presses upon the bones of the hock (Williams). 



In grey horses, however, it has been occasionally observed 

 to be due to a deposit of melanotic matter in the sheath of 

 the great crural nerves, and two cases are recorded in which 

 it was due to exostosis of the ilium pressing on the sciatic 

 nerve. 



Symptoms. — The spasms occurring in chorea are some- 

 times very persistent, at other times they only occur at long 

 intervals. 



They present every degree of intensity, sometimes being 

 very slight, sometimes very severe. 



* Shivering ' is a peculiar nervo- muscular disorder affecting 

 the muscles of the back and posterior extremities. 



When a horse the subject of this affection is backed or 

 turned, the muscles of this region are thrown into clonic 

 spasm, contracting and relaxing irregularly. The tail is 

 often spasmodically elevated, and then depressed. When 

 the horse is trotted forwards, the spasmodic contractions are 

 very seldom developed, but they may be brought into action 

 by the head being turned round rapidly. 



In some instances the spasmodic contractions of the 

 muscles of the loins and thighs come on while the animal is 

 drinking. Though the posterior is more frequently affected 

 than other parts, choreic disturbance may also affect the 

 muscles of the neck and anterior extremities. 



The spasmodic contractions in this region are very 

 variable in severity and in the time of recurrence. 



Morbid Anatomy. — Though in many instances nervous 

 lesions have been found in connection with the brain and 

 cord in chorea, yet no one in particular can be said to be 

 specially characteristic of this affection. 



In some instances tumours have been found in the 



