822 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



cerebral hemispheres. When one of the cerebral peduncles is completely 

 divided it produces paralysis of voluntary movement on the opposite 

 side of the body, with a diminution of the sensibility and vaso-motor 

 paralysis. 



Section of the basis of both cerebral peduncles totally abolishes all 

 voluntary movements, although reflexes apparently of cerebral origin 

 still persist. 



Section of the tegmentum, on the other hand, on both sides entails 

 the loss of these cerebral reflexes, but allows voluntary motion to remain. 



Injury to one cerebral peduncle causes pain and convulsions on the 

 opposite side of the body, while the blood-vessels contract. As the 

 irritative effects pass off these symptoms give place to paralysis. 



5. The Corpora Quadrigemina. — Destruction of the corpora quad- 

 rigemina on one side causes blindness, which ma} 7 be either on the side 

 of the injury or on the opposite side, according to the location of the 

 mutilation. Total destruction causes absolute blindness in both eyes, 

 with the absence of the reflex contraction of the pupil when exposed to 

 the light. In addition to blindness, disturbance of equilibrium and 

 inco-ordination of movement result. When stimulated the pupils have 

 been noticed to dilate either on the same side or the opposite side of the 

 body ; this result is probably produced by conduction of the stimulus to 

 the origin of the sympathetic nerve, for after section of the sympathetic 

 dilatation of the pupil no longer takes place. Stimulation of the right 

 anterior tubercle causes the eyes to deviate to the left, while if a vertical 

 incision is made, so as to separate the right and left corpora quadri- 

 gemina, stimulation of one side only causes this movement to take^place 

 on one side. 



The most striking result of injuries to the corpora quadrigemina 

 are the so-called forced movements, evidently due to peculiar unilateral 

 disturbances of equilibrium causing variations from the symmetrical 

 movements of the two sides of the body. These movements may be of 

 various kinds. In the so-called circus movement, instead of moving in 

 a straight line, the animal runs around in a circle ; rolling movement, 

 where the animal rolls on its long axis, and the index movement, when 

 the anterior part of the body is moved around the posterior part, which 

 remains at rest. These different forms of movement frequently pass into 

 each other, and they may be produced by injury either of the corpus 

 striatum, optic thalamus, cerebral peduncle, pons, middle cerebellar 

 peduncle, and certain parts of the medulla. 



6. The Functions of the Basal Ganglia.— (a) The Corpus 

 Striatum. — We have seen that the corpus striatum consists of two parts, 

 the intra- ventricular portion projecting into the lateral ventricle to form 

 the caudate nucleus, and the external portions the lenticular nucleus. 



