. The chordates. Chordata. Integrative Systems 153 DORSAL NUCLEUS (CLARKE3 COLUMN^ DORSAL ROC GROUND BUNDLE/ SUBSTANTIA GELATI. DORSOMEDIAL Fig. 144. A diagram of a cross section of the mammalian spinal cord, showing the fiber tracts or fasiculi, and the arrangement of nuclei in the gray matter. (After Sobotta. Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.) it above, and a ventral fissure which cuts up into it below (Figs. 143, 144). The somewhat greater part of the nervous substance of the cord consists of nerve-fibers, most of which are medullate
. The chordates. Chordata. Integrative Systems 153 DORSAL NUCLEUS (CLARKE3 COLUMN^ DORSAL ROC GROUND BUNDLE/ SUBSTANTIA GELATI. DORSOMEDIAL Fig. 144. A diagram of a cross section of the mammalian spinal cord, showing the fiber tracts or fasiculi, and the arrangement of nuclei in the gray matter. (After Sobotta. Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.) it above, and a ventral fissure which cuts up into it below (Figs. 143, 144). The somewhat greater part of the nervous substance of the cord consists of nerve-fibers, most of which are medullated (see p. 319). Cell-bodies of neurons constitute the rest of it. Some of these cells be- long to the motor fibers which emerge from the cord in the spinal nerves. Others are cells of association-neurons, one or more of which may be interpolated between the primary afferent neuron and the ulti- mate efferent neuron of a reflex arc. And some are commissural neurons connecting neuron systems of right and left sides of the cord. The vast numbers of fibers which extend lengthwise of the cord are more or less definitely massed into a thick external layer of "white matter" white because of the fatlike substance of the medullary sheaths. The deeper "gray matter" consists of the cell-bodies and the adjacent re- gions of their related fibers which, so far as they lie within the "gray" substance, are usually not medullated. The "gray matter," as seen in a cross section of the cord (Figs. 143, 144), appears as a doroventrally elongated mass on each side of the cord, the two lateral masses being connected by a transverse mass, the gray commissure, which lies near the center of the cord and sur- rounds the small central canal. The dorsal and ventral extensions of the gray region are known, respectively, as dorsal and ventral gray columns. A lateral column, intermediate between dorsal and ven- tral columns, is sometimes recognized. The fibers in the ou
Size: 2294px × 1090px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollect, bookpublisherphiladelphiablakiston
