NERVOUS SYSTEM. 203^ 



the extensors of the hmb. satvhorsc attitude, muscles o'f the 

 eye, prolapsus of the uicmbrana ni'ctitans, cramps of facial 

 muscles, risus sardonicus (canine laugh). Tonic spasms in 

 connection with clonic spasms are also observed in cerebro- 

 spinal meningitis {cramp of the neck). 



All spasms have their origin in the cortex of the cerebrum, 

 the pyramidal tracts, or in the anterior cornua of the spinal 

 cord. Spasms originating in the cerebrum are attended with 

 mental disturbances (epilepsy), not so in case of spinal 

 spasms. 



Rcflc.v spasms are due to irritation of peripheral sensory 

 nerve endings and are of spinal origin ; they are observed 

 when animal parasites occur in the intestines, during the pe- 

 riod of shedding teeth, and in painful gastric and intestinal 

 afifections. 



b. Involuntary movements may be due to irritation 

 of one of the cerebral hemispheres or to paralysis of the op- 

 posite one, also to affections of the midbrain or of the cere- 

 bellum. They always proceed from circumscribed lesions and 

 are therefore known as "symptoms of local origin." Some- 

 times involuntary movements occur in the muscles of the body 

 and extremities, or the usual voluntary movements assume an 

 involuntary character. In such cases animals manifest a 

 desire to "go ahead," trot with head raised or lowered, run 

 against obstacles ; if they get into a corner they are at a loss 

 as to how to get out, frequentl}' they fall down in such cases. 

 Sometimes, but more rarely, they zvalk backzcards. If the 

 cerebral disturbances are unilateral the symptoms tend to be 

 the same. The animals walk in a circle {Reitbahnhezve gun- 

 gen, riding school movements:) they lie down and roll, turn- 

 ing on their long axis, or they fix their hind feet as a pivot, 

 and walk aroimd with their forefeet — move like the hands 

 of a clock. Involuntary movements are most frequently ob- 

 served in chronic and acute hydrocephalus, abscesses, hem- 

 orrhages, tumors and parasites in the brain. Turn sickness,, 

 [gid] ,' of sheep is thus characterized. 



