Page:Popular Science Monthly Volume 6.djvu/91

Rh bearings of the facts, and the intimate relation of the diverse symptoms to each other in tobacco-sickness, it is, perhaps, necessary to map out the pneumogastric nerve and indicate its function, which is not fairly deducible from its name. The origin of nearly every pair of cranial nerves has been traced into the vital bulb, the medulla oblongata, or continuation and expansion of the spinal cord as it passes into the cranium, to blossom into the complex structure of the brain. This tract enters the cranium in six bodies, united in a bulb, and continuing the six strands of the marrow, namely—the two pyramidal continuing the anterior white strands of the spinal stem, the two olivary the interior and partly lateral strands of gray neurine, and the two restiform (corpora restiforma) the posterior white strands. There are two ways of dissecting a brain, each of which has merits of its own for special purposes. The first and more general consists in examining the encephalic mass from above downward, by removing it in successive slices. For descriptive anatomy, and for pathological examination, this method is perhaps preferable. The second consists in examining and unraveling the structure from the spinal bulb upward, by tracing its fasciculi as they expand, radiate, and enlarge; and I am inclined to think that this method has its advantages in tracing the genesis of psychical phenomena. To this bulb all the complex activities of the cerebro-spinal axis finally refer themselves: it is properly the calyx from which spring the three ganglionic masses—the mesocephale, cerebellum, and cerebrum. The par vagum, generally known as the pneumogastric nerves, spring laterally from this bulb, and properly include three pairs of nerves, namely—the glosso-pharyngeal, which supply the base of the tongue with sensation, and connect and coordinate the motions of the organ with those of the pharynx and of the digestive function; the pneumogastric, which, with the preceding, have their origin in filaments springing from the groove between the olivary and restiform bodies; lastly, the spinal accessory, originating laterally from the medulla spinalis, but joining the main stem near its ganglion, and distributed to the lateral muscles of the neck. From the cervical tract of this nerve, which is triple in its origin, spring filaments or strands, that join the sympathetic and lingual nerves, others that proceed directly to the pharynx, and still others known as its cardiac ramifications. The superior laryngeal nerve, distributed to the upper portion of the larynx, and the recurrent nerve, distributed to the muscles of the larynx, are both portions of the pneumogastric system. This pair of nerves passes through the jugular foramen just anterior to the vein of the same name, and separates into three parts. In the foramen it presents a ganglionic expansion, and below it a long gangliform swelling which communicates with the facial, spinal accessory, sympathetic, glossop-haryngeal, and superior spinal nerves—all of which are here gathered into a kind of elongated plexiform bundle. At this point the nerve has the