. The chordates. Chordata. Integrative Systems 171 ventral root, usually emerging from the cord in several small rootlets, consists entirely of motor fibers derived from cells in the gray matter of the cord (Fig. 151). The fibers which enter the cord via the ganglion-cells of the dorsal root come from exteroceptors (in the skin), interoceptors, and proprio- ceptors—, they include both somatic and visceral conductors (Fig. 152). In many vertebrates, but ordinarily not in mammals, the dorsal root contains a relatively small number of visceral motor fibers. These come from cells in the gray m
. The chordates. Chordata. Integrative Systems 171 ventral root, usually emerging from the cord in several small rootlets, consists entirely of motor fibers derived from cells in the gray matter of the cord (Fig. 151). The fibers which enter the cord via the ganglion-cells of the dorsal root come from exteroceptors (in the skin), interoceptors, and proprio- ceptors—, they include both somatic and visceral conductors (Fig. 152). In many vertebrates, but ordinarily not in mammals, the dorsal root contains a relatively small number of visceral motor fibers. These come from cells in the gray matter and pass through the spinal gan- glion, but have no connection with the cells in the ganglion. Of the fibers that constitute the ventral root, some are somatic and some are visceral (Fig. 152). The somatic fibers innervate the striated (voluntary) muscles of the body-wall. The visceral fibers are connected, ICLARKE S COLUMN SOMATIC AA^-H MOTOR %le\ GANGLION CELLS. VISCERAL MOTOR FIBERS Fig. 152. A diagram of neurons of the spinal cord and spinal nerves, showing relations of the neurons to one another and to their end-organs. Somatic sensory fibers are shown by continuous lines, somatic motor fibers by fine dots. Visceral sensory fibers are indicated by short broken lines, visceral motor by long broken lines. (After Plate. Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : Blakiston
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