Upon either side of the anterior median fissure is a small colunin which descends directly' from the-anterior pyramid of the medulla, called the direct pyramidal tract, or column of Tiirck. The remaining portion of the anterior column of the cord, which is much the larger part, is called the funda mental root zone, because it is among the first elements to de velope the spinal cord.
Ou eithe.r side of the posterior median fissure is another small colunin, called the posterior median column, or col umn of Gall, which is supposed to be the respiratory tract of the cord. The remaining portion of the posterior column of the cord, which is much larger than the preceding, is called the posterior root zone, the cuneate fasciculus, or the column ( f I3urdach. It is the sensory column of the spinal cord, dis– ease of which disorders muscular co.ordination, as in the case of progressive locomotor ataxia..
The lateral column of the spinal cord is con.stituted of four fasciculi or tracts, and is included between the lines of emergence of the anterior and posterior roots of the spinal nerves. These tracts are: first—a ribbon like tract situated directly in front of the extremity of the posterior horn of grey matter of either side, and occupying the surface of the lateral column for about half its extent. This tract is con nected in the spinal cord with the grey column of Clarke, and is continued above upon the lateral surface of the medulla and restiform body to the cerebellum. It suffers degenera tion in the disease known as cerebello spinal ataxia, which runs a rapid course, affecting principally the nutritive func tions of the body. Second—beneath the direct cerebellar tract, and anterior to the posterior horn of the grey matter, is a rounded fasciculus called the crossed pyramidal tract. This tract is connected with the vesicular matter of the posterior horn of the cord, and above with the anterior pyramid of the opposite side of the medulla oblongata. It decussates with the crossed pyramidal tract of the opposite half of the spinal cord in the anterior median fissure, at the lower extremity- of the medulla. Beyond the decussation it unites with the opposite direct pyramidal tract to form the anterior pyramid of the opposite side of the medulla. The crossed pyramidal tract is the motor colmnu of the cord, and possibly the office of the direct pyramidal tract is to co-ordinate the muscles of one side of the body- with those of the other. Third- between the columns just described, a-nd the anterior cornu of grey matter and the anterior roots of the spinal nerves, is a large column of fibres forming the anterior portion of the lateral column of the cord. It is called the anterior root zone, and in the spinal cord is supposed to contain longitudinal fibres that connect the segments of the cord together, and also a sensory tract (Gowers) which is continued into the cerebrum. This tract is nearly uniform through
out the spinal cord, and is continued upon the side of the medulla to join the fillet. Fourth—internal to the three tracts just described and lying next to the concave outer surface of the grey column of the cord, is a reticulated column composed of the interlacing fibres of the other fas ciculi of the lateral column of the spinal cord. This tract is the formatio reticularis of the cord, and corresponds to the corona radiata of the cerebrum and cerebellum. It is also called the mixed lateral column, and is not properly a distinct fasciculus of the spinal cord.
Tux MEDULLA OBLONCIATA. —The lower portion of the me_ dulla corresponds to the spinal cord in size, shape, and in the arrangement of its columns, with the exception, that the crossed pyramidal tracts of the lateral columns of the cord, pass forward, decussate with each other, and join the direct pyramidal tracts of the anterior columns, to form the anterior pyramids of the medulla. The posterior median columns of the cord are called, in this situation, the posterior pyramids of the medulla, and terminate above in the clavate nucleii at the apex of the fourth ventricle. The posterior column of the cord (Burdach's) occupies the same relative position in the medulla as in the spinal cord, and terminates above in the restiform nucleus, which is situated in the resti form body above and external to the clavate nucleus. The direct cerebellar tract is continued upward, on the surface of the medulla and the restiform body, to the cerebellum. This tract covers the restiform nucleus so that the latter is not exposed upon the surface. The anterior root zone, or lateral tract of the medulla, passes upward upon the side of the me- • dulla to the lower extremity of the olive where it becomes compressed, between the latter and the restiform body, into a narrow tract which above forms the middle layer of the fillet of the pons. The fundamental root zone above the cord is crowded outward by the anterior pyramid, as far as the lower extremity of the olive. Just below this point, it is flattened in front to accommodate the decussation of the pyramids and disappears from the surface of the medulla to get behind the pyramid between the olive and the raphe, in which situa tion this tract is prismatic in shape, its sides being in relation to the parts just mentioned. Above the olive, it escapes to form a fiat layer of fibres upon the fillet, and terminates above in the testes and brachium posterius.