ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 



.695 



the posterior third of the optic thalamus, determines in the animal 

 lovements in a circle from the injured side toward the sound side. 

 f, however, the lesion be made in the anterior part of the thalamus, 

 ie circular movement is reversed. 



Opinion seems to be divided as to the effect produced by lesion 

 the optic thalamus upon the visual function. It is concluded, how- 

 ler, that the surface of the thalamus (in conjunction with the cor- 

 >ra quadrigemina) presides over sight. 



In addition to the functions just mentioned, the optic thalami 

 lave an influence upon the sensibility of the opposite side of the body, 

 liat is, not conscious sensibility, but that tactile and muscular sensi- 

 >ility necessary for the execution of extended and coordinate move- 

 lents. This is especially so for locomotion without the aid of the 

 ill. These movements, then, are none else than reflex. They re- 

 md to the impressions made upon the sensory surface of the body 

 md reflected in the large, excitomotor centers, viz., the thalami. The 

 mlami are relay centers for the sensory tract. 



Thus, while a normal individual walks along a clear street, per- 

 haps he thinks of his movements but once. During that short time 

 his will directs his volitional impulses; the rest of his walk, on the 

 contrary, is executed almost automatically. In this case the excita- 

 ions take their departure from impressions upon the body by the 

 round, space, weight of the body, etc. These impressions are all 

 imed up in the optic thalami, from which they return, coordinated, 

 long the nerves of motion. 



When the striated bodies are irritated they do not provoke any 

 signs of pain. Though the animal remains relatively quiet under 

 iblation of the hemispheres, yet it is seized with violent and con- 

 ilsive contractions in the opposite half of the body when the striated 

 ly is hardly reached. This response is especially marked in the 

 iticulo-striate part of the internal capsule. By stimulating a striated 

 ly with electricity, tetanus in the opposite half of the body has 

 obtained. The corpora striata are motor relay centers. They also 

 mtain a thermogenic center. 



Experimental Physiology of Cerebral Hemispheres. 



There are two great means that experimental physiology has at 

 disposal, viz. : stimulation (electrical, mechanical, chemical, and 

 lermal) and removal. These are likewise applied to the most im- 

 >rtant and noble part of the nervous apparatus: the cerebral hemi- 

 spheres. The experimental results are then compared with those 



