284 SPECIAL PHYSIOLOGY. 



connected with the optic thalami, and the motor tracts with the cor- 

 pora striata and corpora quadrigemina. Division of both peduncles 

 is followed by complete loss of sensibility and voluntary movements 

 in the body. When one peduncle is partially divided, remarkable 

 rotatory movements ensue, from the injured to the sound side, which 

 have been attributed to a loss of the controlling power of the cere- 

 brum over the half of the body opposite to the injury ; the circles of 

 movement are larger, the nearer the section is made to the cerebrum. 

 Complete division of one peduncle causes the animal to fall on the op- 

 posite side, because it paralyzes that side, though the reflex functions 

 remain intact. 



Irritation of the peduncles, after the brain has been removed, causes 

 contractions in the muscles generally, and also in the stomach, intes- 

 tines, and bladder ; these effects show conductive power, partly through 

 the pons, medulla, spinal cord, and spinal nerves, and partly through 

 the sympathetic, which is connected not only with the medulla and 

 cord, but also with parts of the brain higher up. 



As to the gray masses, sometimes named the cerebral ganglia, found 

 at the base of the brain, the gray matter of the corpora quadrigemina 

 appears to be associated with the function of sight; for removal of 

 these parts causes blindness, which likewise usually follows their de- 

 struction by disease. Atrophy or wasting of these bodies, may result 

 from atrophy of the eyes. The destruction of one causes loss of sight 

 in the opposite eye, and temporary debility of the opposite side of the 

 whole body. The corpora quadrigemina are also highly irritable, and 

 exercise reflex functions of an extremely active and important kind. 

 Thus, irritation of both, or even of one. of these gray centres, pro- 

 duces contraction of both pupils, and, during life, such movements 

 are doubtless caused by impressions conveyed from the retinae, through 

 the afferent fibres of the optic nerves and tracts ; and the experiment 

 last mentioned, on one of these bodies, is regarded as a proof of the 

 transmission of impressions from both retinae, backwards through the 

 optic commissure, along both optic tracts. Partial removal of the cor- 

 pora quadrigemina produces partial blindness of a temporary kind, 

 debility of the muscles on the opposite side of the body, and some- 

 times giddiness, or slight rotatory movements ; possibly from the in- 

 terference with the sense of sight. Their complete removal is followed 

 by total blindness, and by dilatation and immobility of the pupil. /The 

 general consciousness is not interfered with. Besides the slight rota- 

 tory movements just mentioned, general convulsions sometimes follow 

 experiments on these parts ; but these are both supposed to be owing 

 to unavoidable injury, or irritation, of deeper-seated parts. That the 

 corpora quadrigemina are connected with the exercise of the function 

 of sight, is therefore undoubted, and it is probable that they are either 

 the actual centres of visual sense, or the essential paths for the recep- 

 tion and conduction of visual impressions to a common sensorium. It 

 is, perhaps, through this office, that the effects of injuries of these 

 centres, on the general muscular movements, may be explained, for 

 vertigo may be produced by blinding one eye, or by causing the 

 humors of one eyeball to escape. 



