Page:Popular Science Monthly Volume 26.djvu/769

Rh As to the functions, in detail, of the optic thalami and the corpora striata, hardly anything is known. It will be remembered that these bodies are the rather large masses situated in the chambers of the cerebral hemispheres. There is no reasonable doubt, however, that they are concerned with sensations and motions; the thalami having to do with impressions which are the physical antecedents of sensations, and the striata with the execution of movements. This conclusion is confirmed by pathology. Disease of the striatum is followed by paralysis on the opposite side of the body. Disease of the thalamus, while not always so uniform in its testimony, does still, sometimes, give striking evidence of a sensory significance of the organ. It should be distinctly borne in mind, when speaking of these bodies, that paralysis of sensation and of voluntary motion may be produced by lesions in the cell-matter of the cerebrum apart from any injury to the thalamus and striatum; it should also be remembered that destruction of these basal ganglia breaks the connection between the cell-matter of the cerebrum and the surface of the body, so that the cerebral hemispheres can not perform their functions. It may, therefore, be true, as many maintain, that these organs are not at all directly associated with consciousness, their function being to adjust the connections of sensory and motor fibers with the cerebrum. This general conclusion need not be taken as supporting the fanciful opinions of Luys. Luys believes that in the thalami sensorial impressions "are for the first time condensed, stored up, and elaborated by the individual action of the elements that they disturb in their passage. It is thence that they are launched forth into the different regions of the cortical periphery (cell-matter of the cerebrum) in a new form, intellectualized in some way to serve as exciting materials for the activity of the cells of the cortical substance." According to the same writer, the striata do for our volitions the exact reverse of that which is done by the thalami for our sensory impressions. "It is in the midst of the tissues of the striata that the influence of volition is first received at the moment when it emerges from the psycho-motor centers of the cerebral cortex. There it makes its first halt in its descending evolution and enters into a more intimate relation with the organic substratum destined to produce its external manifestations—in one word, materializes itself." There can be no doubt about the justice of describing this conclusion as fanciful and quite beyond the data.

We have outlined the structure of the cerebro-spinal system, and have stated what may fairly be set down as established concerning the functions of this system up to the cerebral hemispheres. With respect to the presence of consciousness in the parts already examined, it is plain that opinions radically differ. Some maintain that consciousness is not manifested apart from the action of the cerebrum, that all nerve-activities below this organ are reflex, their only distinctions being in the matter of complexity. Others are equally positive that