74 THE NERVOUS SYSTEM 



The Optic Thalami. These large nuclei in the middle of each hemi- 

 sphere have shown in experiments and in natural lesions so large a variety 

 of apparent functions that to name their general purpose or purposes 

 in the nervous system is at present impossible. They seem to be centers 

 of correlation between afferent impulses and those which produce move- 

 ment. Perhaps, as their name implies, vision is especially concerned, for 

 they are in the nature of nerve-currents passing from the eyes to the 

 nerve-centers in the occipital lobes, and when an eye is destroyed the 

 thalamus of the opposite side degenerates somewhat. Lesions in these 

 nuclei produce undoubtedly a rise of body- temperature. They also dis- 

 turb severely emotional expression. Thus, in one case a man who was 

 found after death to have a large tumor of one thalamus could imitate 

 a smile perfectly well (by using probably his voluntary motor -cortex), 

 but on hearing anything humorous that side of his face opposite to the 

 tumor remained blank, although the other side of his face smiled natur- 

 ally. Such cases prove that one of the functions of the thalami is coor- 

 dination in the muscular expression of the emotions. These nuclei inter- 

 vene between the incoming afferent impulses and the cortex of the brain 

 around them, but exactly what they do to these impulses is not yet fully 

 understood. 



The Corpora Striata. These consist of two parts: The lenticular 

 nucleus and the caudate nucleus. Lines of white fibers extend through 

 the gray mass of the corpus (giving it its name). Little is known about 

 the function of these bodies, less than about any other part of the brain. 

 Stimulation of one mechanically or electrically causes convulsions of the 

 muscles on the opposite side of the body, while destruction of one corpus 

 gives rise to paralysis of these muscles. This paralysis appears to be 

 transitory if only the gray part of the organ is destroyed. Several experi- 

 menters have seen a rise of body-temperature follow irritation of the gray 

 matter, but this follows also from stimulation of various regions of the 

 cortex cerebri. The fact, however, is suggestive of a possibility that the 

 corpora striata may be concerned in the regulation of the muscular 

 metabolism, and this largely determines the heat-production of the body. 



Nothnagel and Rezek have recently corroborated the conclusions of 

 Magendie that the corpora striata are organs concerned in the reflex 

 coordination of the muscles of locomotion. Destruction of part of the 

 caudate nucleus causes rabbits to go in circles rather than straight ahead. 

 This part of the nucleus Nothnagel names the nodus cursorius. 



The Corpora Quadrigemina. These are in the roof of the aqueduct of 

 Sylvius, above the cerebellum, and in front of the lower posterior part of 

 the corpus callosum. They are composed of white fibers outside and of 

 gray matter within. Two of the four small bodies are anterior and two 

 posterior. They apparently differ much in function. Through the ante- 

 rior pair the internal capsule is connected with the optic tract from the 

 retina to the occipital lobe, while similarly the posterior pair connects the 

 internal capsule with the paths between the cochlea and temporosphe- 

 noidal cortex. Monakow showed the connection of the cortex of the 



