THE: GANGLIONIC SYSTEAI : The grey.matter of the spinal cord is dispose(' in two columns, one on each side, enclosed by the white matter of the cord. These columns are united by a grey conmaissure, which contains in its middle the cen tral canal of the cord, and they are projected forward and backward into cornua, which are the origins of the roots of the spinal nerves. The anterior horns of grey mat ter are motor in function, and the posterior horns contain the centers of the sensory roots of the spinal nerves. The sens ory roots are associated with the sympathetic nervous system by ganglia, near their insertion into the spinal cord. The vesicular columns of Clarke extend along the junction of the posterior cornua and the posterior surface of the grey cora missure, one on each side ot the posterior median fissure of the cord. The anterior horns of the grey matter are inter rupted at the upper extremity of the spinal cord by the decussation of the crossed pyramidal tracts, and above the decussation they gradually approach the median line of the medulla, while the posterior horns gradually diverge or are turned ontward.
In the fourth ventricle the grey columns are exposed upon its floor to form the fasciculi teretes; the motor nerve centers being disposed internally along the sides of the median fis sure, and the sensory centers upon the outer sides of the ven tricle. The grey matter above the fourth ventricle encloses the iter, and contains the centers that control the movements of the eyes. Above the iter, it spreads upon the sides and the floor of the third ventricle; and the sides of the ventricle are united in the, center by the grey or middle commissure of the third ventricle. Ou the floor of the ventricle the grey matter is continuous with the tuber cinereum, infundibulum, and pituitary body, and iu front with the lamina cinerea and grey matter of the hemispheres.
The greater ganglia of the cerebro-spinal axis are : the hemispherical, and the external and internal basal ganglia, of the cerebrum ; the hemispherical ganglia, the corpora dentata and the ganglia of the pons Varolii, or the internal and external basal ganglia, of the cerebelltim.
The lesser ganglia are : the olivary bodies, restiform and clavate nuclei, of the medulla oblongata,: the locus niger, cot pora quadrigemina, pineal body, the geniculate bodies, the corpora albicantia, and the red nuclei, in and about the crura cerebri.
Other cerebral ganglia are: the claustrum, and the substan tia perforata. The olfactory bulbs, though situated in the cranial cavity, may properly be classed with the spinal ganglia.
Of the white substance of the spinal cord, the fasciculi of which it is composed are rearranged as they pass upward through the several portions of the central nervous system, and are associated with the grey masses above mentioned. The direct pyramidal tract, and the crossed pyramidal tract of the opposite side of the spinal cord, unite to form the anterior pyramid of the medulla oblongata. The anterior pyramid enters the polls Varolii and is associated with the reticulated layer of the anterior portion of that body. This layer of the pons has been described as being connected above with the crusta of the crura cerebri, and laterally with the deep layer of the middle peduncles of the cerebellum. It also con tains a large amount of vesicular matter, and is the ganglion of the pons Varolii. The crusta is the continuation of the pyramidal tract above the pons, much enlarged by an accession of fibres from this body, and is distributed to the lenticular nucleus, and through the internal capsule, to that part of the hemispherical ganglion situated about the fissure of Rolando, which is the motor area of the hemisphere. The fibres de rived from the crusta occupy the middle portion of the inter nal capsule. The entire tract with its associations, just described, constitute the motor system of the cerebrospinal axis.