Page:Popular Science Monthly Volume 26.djvu/756

 composed almost wholly of fibers passing transversely between the two sides; it makes the hemispheres anatomically and physiologically one. Were we to continue our section straight through the middle line of the callosum, we should reach a lateral chamber in each hemisphere. This chamber contains two rather large bodies called the corpus striatum and the optic thalamus. The stems or crura cerebri previously mentioned pass into these bodies before spreading out through the hemispheres. The striatum is shaped somewhat like a pear; it lies in the chamber with its small end forward, and is composed of alternate layers of cell and fiber matter. The thalamus is ovoid, and presents an almost continuous mass of cell-matter traversed by fibers. The researches of J. Luys, of which a condensed account may be found in Vol. XXXIX of the "International Scientific Series," are most interesting as respects both anatomy and functions of the thalamus. Luys has discovered four isolated ganglia of cell-matter in the thalamus, situated one behind the other. He has also traced connections between these ganglia and certain organs of special sense. Behind and between the thalami are two smaller bodies called the optic lobes. They consist of two rounded eminences, the anterior ones being called the nates, the posterior the testes. The optic tracts, forming the optic commissure previously mentioned, proceed from the nates, the testes being connected by a band of fiber-matter with the cerebellum; commissural fibers join these optic lobes with the thalami.

I have now named the leading portions of the cerebro-spinal system, and have indicated their general connections with one another. They are nothing more nor less than a series of nerve-ganglia connected among themselves by transverse and longitudinal commissures. This system shows us matter in its most highly organized condition; further, this system shows us matter in some positive and necessary relation to consciousness.

The conclusions which we draw respecting the nature of this relation must, as has been said, be determined by a comparison of the

 consisting of many smaller cords wrapped up in a common sheath. (Quain, after Sir C. Bell.) A, the nerve; B, a single cord drawn out from the rest. Magnified several diameters.

known functions of the system with the distinctive characteristics of consciousness. I come, therefore, now to consider the functions of the cerebro-spinal system in so far as these are known, and in so far as they may be inferred from recent experiments and pathology.

—Nerve-matter has, for its general office-work, to bind together the parts of our body. Wherever this matter is divided there is a peculiar division in the