Functions of the Basal Ganglia. 627 



The tuber cinereum and the pituitary gland, or hypophysis, lying un- 

 der the third ventricle, are small bodies of uncertain function. 



The optic thalami, corpora quadrigemina and corpora striata are 

 paired or doubled, the pineal gland, tuber cinereum and pituitary gland 

 are single, and median in position. 



Corpora Quadrigemina. Among the invertebrates, the part of the 

 brain answering to the corpora quadrigemina, or optic lobes, is rela- 

 tively more highly developed than in the vertebrates, and bears a direct 

 proportion to the size of the eyes. Among the lower vertebrates these 

 ganglions are relatively larger than in the higher; but amongst the mam- 

 mals the high development of the other organs of sense and the cere- 

 brum, causing a corresponding development of their brain ganglia, ren- 

 ders the optic organs of less relative importance. In birds, the optic 

 lobes are much larger, in proportion to the cerebrum, than in man and 

 the higher mammals, and correspondingly the sight stimuli enter more 

 largely into their activities. In fishes, birds and reptiles, the optic 

 lobes consist of two lobes or tubercles, one on each side. They are 

 called the bigemina ; in the mammals there are four, two on each side, 

 hence the name "quadrigemina." 



In all animals these ganglia, or tubercles, are the organs of sight, 

 directly sensitive to the light stimuli from the retina. Any injury to 

 them is a damage to the faculty of seeing, and to those qualities of 

 mental action which depend upon light. Partial loss of the corpora 

 quadrigemina on one side, produces partial loss of power and temporary 

 blindness on the opposite side of the body, without, however, neces- 

 sarily destroying the mobility of the pupil. But if these ganglia be 

 totally destroyed on one side, it will cause total and permanent blind- 

 ness and immobility of the pupil, with temporary muscular weakness, 

 on the opposite side. Sometimes, when injuries are artificially produced 

 upon animals under experiment, the destruction of the tubercles of OUQ 

 side produces a tendency to turn about as if the animal were giddy. 

 Irritation of one tubercle produces contraction of both pupils. Blind- 

 ness is, in many cases, caused by disease in one or both tubercles, and 

 sometimes by disease in the adjoining parts of the crura cerebri. . If 

 the corpora quadrigemina on one side be pricked with a pin, it oauses 

 convulsions of the eye of the opposite side. The cause of the turnings 

 and rollings is to be ascribed to convulsive contractions in some of the 

 muscles on one side of the body. These spasmodic contractions always 

 accompany the turnings, and their chief cause is irritation of some part 

 of the governing brain center, which irritation may follow the slightest 

 puncture. Rolling is merely a more intense result of the contractions 

 that produce turning. 



The stimulation of the corpora quadrigemina ( optic lobes ) of rabbits 



