Page:Popular Science Monthly Volume 26.djvu/758

 or "centripetal" fiber which shall proceed to another collection of cell-matter. In the cerebro-spinal system we have the lowest nerve-arc brought into close anatomical relation with the large cell-mass of the cerebral hemispheres, as well as with the lower cell-masses, by ascending and descending fibers.

I am now to indicate the functions of the parts of this system previously described, and first the spinal cord. This organ has two distinct functions—these are transmission of motions and independent nerve activity. As conductor of motions the cord is related to the higher encephalic centers. By transmission of motions from the surface of the body along an afferent fiber to the cell-mass of this cord, and thence to the brain, sensations are made possible. By transmission of motions from the brain along efferent fibers down the antero-lateral columns of the cord to the anterior roots, and thence to muscles supplied by these roots, voluntary movements are made possible. This teaching should be emphasized. We are dependent on the anatomical

 (Allen Thomson.) 1, 1. great longitudinal fissure; 2, 2&prime;, 2&Prime;, convolutions of under surface of frontal lobe; 3, 3, 3, prolongation to base of the fissure of Sylvius; 4, 4&prime;, 4&Prime;, convolutions of the temporal lobe; 5, 5&prime;, occipital lobe; 6. anterior pyramids of medulla; +, posterior extremity of median lobe of cerebellum; 7, 8, 9, 10, lobules of the lateral lobe of the cerebellum. I-IX. Cranial nerves, all but the first more fully seen in the next figure. The ninth nerve of the right side has been removed. X. First cervical nerve.

integrity of the spinal cord and encephalic centers for any direct sensation, knowledge of things affecting nine tenths of our body, and also for any exercise of volition upon these parts of our body. Consciousness and volition, as far as they relate to any direct connection between ourselves and a large part of our physical organism, are entirely