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The inferior mesenteric ganglia are incorporated in the inferior mesenteric plexus. This plexus surrounds the inferior mesenteric artery and is connected with each sympathetic trunk by means of several slender rami, the lumbar splanchnic nerves, and with the celiac and superior mesenteric plexuses by means of intermesenteric nerves. The splanchnic nerves in the upper lumbar segments do not enter the inferior meseateric plexus directly, but fuse with the intermesenteric nerves above the level of the plexus. Some rami arising from the inferior mesenteric plexus extend distalward along the inferior mesenteric artery and its branches ; others join the hypogastric plexuses. Some fibers also join the plexus on the aorta.Preganglionic fibers reach the inferior mesenteric ganglia via the lumbar splanchnic nerves. Most of the fibers of the intermesenteric nerves, except components of the lumbar splanchnic nerves, probably do not effect synaptic connections in the inferior mesenteric ganglia, but continue distalward in the hypogastric plexus. These ganglia, consequently, may be regarded as essentially sympathetic. Their constituent ganglion cells, like those of the sympathetic trunk ganglia, have commonly been regarded exclusively as distal neurons in visceral efferent conduction pathways. Certain experimental data, however, support the assumption that nervous reactions may be mediated through the inferior mesenteric ganglia in the absence of nerve impulses which reach these ganglia from 371

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The pelvic viscera arc? iiiiiervated through tlic hypogastric and pelvic nerves and the pelvic plexuses. The .hypogastric iierves are related to the sympathetic division of the autonomic nervous system ; the pelvic nerves to the parasympathetic division. Each pelvic plexus consists of a complex meshwork of iiitcrlacing bundles of nerve fibers and numerou~ small ganglia. The fibers are derived in part from both the hypogastric and pelvic nerves and in part from the ganglia within the plexus. Each pelvic plexus gives rise to subsidiary plexuses which accompany the hypogastric artery and its branches, viz., the hemorrhoidal, vesical, prostatic or uterine, and vaginal plexuses, through which nerve fibers are supplied to the pelvic viscera. Certain of the pelvic organs, particularly the large intestine and the urinary bladder, also contain intramural ganglia.Langley and Anderson (1894) pointed out that some preganglionic fibers which enter the inferior mesenteric plexus do not terminate in that plexus but extend distalward in the hypogastric nerves. They also pointed out that the nerves which arise from the lower lumbar and sacral se,gnenis of the sympathetic trunks and join the hypogastric nerves or the pelvic plexuses contain numerous myelinatecl fibers. Certain other investigators, particularly Stewart (18Xl), advanced data which seem to support tlie assumption that preganglionic