. An elementary course of practical zoology. Zoology. X SPINAL AND CEREBRAL NERVES 163 Origin of the Spinal Nerves.—The mode of origin of the nerves from the spinal cord is peculiar and characteristic. Traced towards the cord, each nerve is found, on reaching the intervertebral foramen from which it emerges, to divide into two—a dorsal root which springs from the dorsal, and a ventral root which arises from the ventral region of the cord (Fig. 52, , ). The dorsal root is distinguished from the ventral by being dilated into a ganglion (gn). In Fig. 51 these ganglia lie hidden within certa
. An elementary course of practical zoology. Zoology. X SPINAL AND CEREBRAL NERVES 163 Origin of the Spinal Nerves.—The mode of origin of the nerves from the spinal cord is peculiar and characteristic. Traced towards the cord, each nerve is found, on reaching the intervertebral foramen from which it emerges, to divide into two—a dorsal root which springs from the dorsal, and a ventral root which arises from the ventral region of the cord (Fig. 52, , ). The dorsal root is distinguished from the ventral by being dilated into a ganglion (gn). In Fig. 51 these ganglia lie hidden within certain calcareous bodies (C) in this region. Fig. 52.—Transverse section through the vertebra! column and cord, to show the mode of origin of the spinal nerves. c. c. central canal ; en. centrum ; dorsal fissure ; d. dura mater ; d. r, dorsal root; g. m. grey matter ; gn. ganglion of dorsal root ; 71. a. neural arch ; w. sp. neural spine ; p. 111. pia mater (the reference line should stop at the margin of the cord) ; t. nerve trunk ; Tr. pr. transverse process ; t'. /. \entral fissure ; V. r. ventral root; w. i)i. white matter. (After Howes.) Cerebral Nerves.—There are ten pairs of cerebral nerves some of which are purely sensory, some purely motor, some mixed. The first or olfactory nerves (Fig. 49, /) arise from the olfactory lobes, and pass through the holes in the trans- verse partition of the girdle-bone. Each is distributed to the mucous membrane of the nasal sac or organ of smell of the same side, and is purely sensory. The second or optic (Fig. 49 //) is a large nerve which springs from the ventral surface of the 'tween-brain. At M 2. 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 Parker, T. Jeffery (Thomas Jeffery), 1850-1897; Parker, William Newton, joint author. Londo
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