Nervous and mental diseases . e have still furtherdivision of the tracts. These are shown in LOCALIZATION. 339 figure 125 for the ascending degenerations which follow complete divi-sion of the cord, and for the descending degenerations after similar lesions. The H -shaped cross-section of the gray matter shows numerous cell-bodies. Of these the anterior cornual groups are the best understoodand contain the cell-bodies of the lower motor neuron through whichmotor, trophic, and vasomotor influences are exercised over the muscles,bones, and skin. The central canal is situated in the gray commissu
Nervous and mental diseases . e have still furtherdivision of the tracts. These are shown in LOCALIZATION. 339 figure 125 for the ascending degenerations which follow complete divi-sion of the cord, and for the descending degenerations after similar lesions. The H -shaped cross-section of the gray matter shows numerous cell-bodies. Of these the anterior cornual groups are the best understoodand contain the cell-bodies of the lower motor neuron through whichmotor, trophic, and vasomotor influences are exercised over the muscles,bones, and skin. The central canal is situated in the gray essential elements of the cord are supported by fibrous tissue whichis continuous with the penetrating septa of the pi a mater. The circulation in the cord is one of its most important anatomicalfeatures. Many of the cord diseases are due to vascular lesions orinfections, and both their vertical distribution and lateral outlines intransverse sections mav be limited to the corresponding arterial fields. olumn tflissauer. Fig. 122.—Cross-section of cervical spinal cord, showing its anatomical subdivisions (Schaefer). The arterial supply of the cord consists of two systems, anterior andposterior. The anterior spinal artery, arising within the skull by tworoots from the vertebrals, extends the entire length of the cord at theanterior fissure (Fig. 127). It is reinforced by branches from the inter-costal, lumbar, and sacral arteries, which follow the corresponding nervesinto the spinal canal and accompany the nerve-roots to the cord. Theanterior spinal artery gives off about three hundred branches, calledanterior median arteries, which penetrate the anterior fissure at a rightangle to the parent stem. At the commissure they enter the cord andwithout dividing turn toward the right or left anterior horn. At theneck of the horn the artery divides into an anterior branch to theanterior horn and a posterior branch which is distributed to the neckand to a portion of the posterior
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