THE NERVOUS SYSTEM AND CONSCIOUSNESS. 733 



cells, while it is twenty-five per cent in the fibers. This fact, taken 

 in connection with the much greater provision for distribution of blood 

 to the cell-mass, is strongly confirmatory of Mr. Spencer's opinion that 

 the cells liberate motion by destruction of their substance, and the 

 fibers by isomeric transformation. 



The nerve-matter thus described is distributed over the body by 

 two divisions — the great sympathetic and the cerebro-spinal systems. 

 The latter alone concerns us in this paper. The nerve-matter of the 

 cerebro-spinal system is found in the spinal cord and the encephalon. 

 The spinal cord is a nearly cylindrical mass, from fifteen to eighteen 

 inches long, and connected at its anterior extremity with the brain. 



The cell-matter lies at the center and forms a continuous ganglionic 

 band. The fibers are on the outside, and are divested of their tubular 

 sheath. The central cell-matter of the cord is curiously shaped into 

 two partial crescents, which are connected with one another by cell- 

 substance called the gray commissure. Thirty- 

 one pairs of nerves arise from the sides of the 

 spinal cord and supply the entire body, except 

 the head and other parts receiving branches 

 from the cranial nerves. Each nerve leaving 

 the cord contains, at its origin, all the filaments 

 into which it may afterward be divided. Each 

 filament or fiber remains anatomically distinct 

 throuo-hout its course. The fibers in the cord 

 are connected by a commissure called the white 

 commissure, and those on different sides of the 

 cord extend longitudinally and are parallel to 

 each other. Some of these longitudinal fibers, 

 passing from below upward, convey impulses to 

 the cord or brain ; others, descending from the 

 brain and higher parts of the cord, transfer mo- 

 tor impulses to muscles. Without presenting 



more anatomical detail, it is sufficient to say that the halves of the 

 cord are unified by the fibers of the commissures, and that it works as 

 one organ. 



The nerve-matter of the encephalon is divided into three principal 

 parts, viz., the medulla oblongata, the cerebellum, and the cerebrum. 

 The medulla is a continuation and enlargement of the spinal cord at 

 its entrance into the cranial cavity. Here the anterior fibers of the 

 cord become the anterior pyramids of the medulla, while the posterior 

 fibers of the cord are called the restiform bodies. Immediately to the 

 side of the pyramids are projections called the olivary bodies. The 

 medulla is about one and one quarter of an inch long, and one inch 

 broad at the widest part. There is cell-matter in the restiform and 

 olivary bodies, a part of this matter being continuous with the cell- 

 matter of the cord, and a part consisting of independent masses. Di- 



FiG. 1.— Human Nerve -Fr- 



BEES OF DIFFERENT SIZES 



(Kolliker). a, a, a, healthy 

 fibers, the largest of which 

 is " dark -bordered " ; 6, 6, 

 fibers altered by exposure. 

 Magnified 350 diameters. 



