Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/916

Rh 862 ANATOMY [NERVOUS nerve fibres in their turn branch, accompanied by a splitting of the axial cylinder, and these branches usually lose the niedullated character. The mode of termination of these very delicate branches has been a subject of much dispute. Beale described them as forming a minute net work, situated on the exterior of the sarcolemma, but in contact with it, and the fibres of this nervous network were distinctly nucleated. Other observers have, however, described peculiar bodies, called motorial end-plates, at the extremity of these nerves. These end-plates consist of a clump of richly nucleated protoplasm, somewhat oval or perhaps irregular in form, into which the axial cylinder of the nerve fibre penetrates. The exact position of these end-plates in relation to the muscular fibres is difficult to determine. Krause holds that they lie outside the sarco lemma, but adherent to it; whilst Kiihne, Margo, and Rouget maintain that the end-plate lies within the sarco- lemma, and that the nerve fibre has to pierce that mem brane before it can enter the end-plate. After the axial cylinder has entered the end-plate it subdivides into very minute branches. Each muscular fibre has apparently only a single end-plate, and consequently only a single axial cylinder in connection with it. In the non-striped muscles the nerves are distributed in the connective tissue which separates the fasciculi from each other. Here they form plexuses, which in some loca lities, as in the myenteric plexus of Auerbach in the mus cular coat of the intestines, have collections of nerve cells, forming microscopic ganglia lying in them. From these plexuses fibres arise which subdivide into delicate non- medullated fibres possessing nuclei. These delicate fibres form still finer plexuses, which in their turn give origin to minute fibres, which pass between the muscular fibre cells to form a still more minute intra-muscular network. Frankenhauser maintains that the delicate nerve fibrils which arise from this terminal network penetrate the muscular fibre cells, enter the nucleus, and terminate in the nucleolus; but Arnold considers that, after having entered the nucleus, the fibril again gives off a filament, which passes out of the cell to join the intra-muscular plexus; the ending of the nerve, therefore, within the nucleus is only apparent, and is rather to be regarded as the nodal point of a fine intra-nuclear plexus. The termination of the sensory nerves in the mucous mem branes has been especially studied in the conjunctiva, the mucous membrane of the soft palate, and the glans of the penis and clitoris. In these parts Krause discovered oval or globular end-bodies, which consisted of a soft, homogeneous substance invested by a nucleated capsule of connective tissue. A nerve fibre pierces the capsule and terminates in the interior of the end-body, which forms a bulbous enlarge ment at the end of the nerve, and is called the end-bulb. After the nerve has entered the end-bulb, it may consist only of the axial cylinder and terminate in a pointed extremity, or it may twist upon itself and form a coil within the end-bulb. When the structure of the skin is described, it will be seen that the ending of the nerves in the cutaneous papillae bears a general resemblance to their termination in the end-bulbs of a mucous mem brane. But in certain of the mucous membranes delicate nerves have been traced into the layer of epithelium, situated on the free surface of the membrane. Petermoller described nerve fibres continuous with the nerves of the cornea pass ing into the layer of conjunctival epithelium on the front of the cornea. Klein recognised an intra-epithelial nervous network in the same locality. Chrschtschonovitsch traced non - niedullated nerve fibres proceeding from a sub- epithelial network into the deeper epithelial layers of the vaginal mucous membrane, and similar nerve fibres have been seen by Elin to end in the epithelial investment of the mucous membrane of the mouth. Connected with the sensory nerves in some localities are Pacin the remarkable bodies named the Corpuscles of Pacini, cor l )U which were the first terminal organs discovered in connec tion with the peripheral distribution of the nerves. These corpuscles have been found attached to the nerves which pass to the skin of the fingers and toes, to the nerves which supply the skin of the neck and arm, to the inter costal nerves, to the nerves of the joints, to the nerves of the periosteum, to the nerves of the genital organs, and to the mesenteric nerves. In cats they are often extremely abundant both in the mesentery and omenta. A Pacinian fio. G2. 1. Nerves of one finger with the Pacinian corpuscles attached. 2, a I acinian corpuscle X 350; a, stalk or peduncle; 6, nerve fibre in still k; c, external layers of cr.psule; d, inner layers;, non-medullated nerve fibre in the central core ; /, branching of terminal end of nervo fibre. (From A. KiiUiker.) corpuscle can be seen by the naked eye, and looks like a minute grain from -j^th to ^th inch long. It is elliptical in form, and may either be sessile or attached to the nerve stem by a slender stalk. Examined microscopically, it is seen to consist of numerous layers of connective tissue concentrically arranged, which form its capsule, and surround a central core. Numerous connective tissue cor puscles may be seen in the concentric layers, and Hoyer has recently shown that an endothelial-like appearance exists on the inner surface of the corpuscle. Entering one polo of the corpuscle is a nerve fibre which extends along the axial core for a considerable distance, and usually termi-