ANATOMICAL CHARACTERS. 417 



tell US of any structural alterations which must be regarded as 

 specially characteristic of chorea. In several such examina- 

 tions I have found that many and different lesions of the 

 textures connected Avith and entering into the composition of 

 the nerve-centres were easily discoverable. Chief of these may 

 be mentioned as thickening of the serous covering of the brain, 

 effusion in the sub-arachnoid cavity of brain and cord, visible 

 changes of texture, chiefly of a sclerous character, with vascular 

 injection of the cord, and particularly of the central ganglia 

 of the brain, the optic thalami, and corpora striata. 



Sjnnptoms. — These are chiefly motorial, and, even when most 

 severe, do not seem productive of pain or weariness. The 

 muscular spasms vary much both in frequency and severity. 

 They may only occur at long intervals and on j)articular occa- 

 sions, as when the animal is excited, which in all cases seems 

 to produce an aggravation of the contractions ; or they may 

 exist, although rarely in the horse, in uninterrupted sequence, 

 scarcely modified when the animal is at rest. They may in 

 their manifestation scarcely attract attention, so little do they 

 disturb the natural movement of the parts acted upon by the 

 affected muscles ; or they may be so severe as visibly to impair 

 movement and impart a most singular appearance to the 

 member acted upon. 



Amongst horses, as already noted, choreic manifestations 

 almost invariably show themselves as an independent affection, 

 not as a sequel of some other diseased condition. The sjDasms 

 chiefly exhibit themselves in connection with the muscles of 

 the back and posterior parts. Appearing often early in life, 

 this nervo-muscular disturbance does not in the horse, as in 

 many other animals, exhibit with age a tendency to disappear. 

 The muscular spasms, or twitchings, are in him, as a rule, less 

 developed and more liable to be overlooked, than in some 

 other animals, and may only be observed when he is moved in 

 certain directions, so as to call mto action a particular set of 

 muscles. 



In the most commonly encountered manifestation of this 

 diseased condition, from the peculiar tremulous nature of the 

 muscular contractions, the affected animals are very generally 

 designated ' shiverers.' 



In examining horses suspected to be affected with this 



27 



