(d) One or two delicate filaments have been observed by Fontana, Hirzel, and Arnold to pass from the cavernous plexus to the pituitary body. As this body is said to receive filaments from the sympathetic cords of either side, it has been supposed to hold the same rela tion to these as the ganglion impar or coccy geal ganglion at the opposite extremity of the trunk. Bock regards the filaments, however, which have been described as entering the pituitary body, as solely destined for its ves sels, terminating in their coats. Weber states that he has examined with the greatest care the supposed communication between the synipathetic and pituitary body in mammals and birds, but failed to convince himself that any such communication exists. (e) Arterial branches, accompanying the branches of the internal carotid arteries. These are described by Chaussier* and Ribes as passing not only along the anterior and middle cerebral arteries, but also along the branches of the ophthalmic artery, forming minute plexuses upon them. One of these plexuses is described by these authors, as well as by Rusel and Langenbeck, as accompanying the central artery of the retina into the eyeball. Ribes has also traced filaments from the cavernous plexus upon the anterior communicating arteries, by means of which the sympathetic cords of either side are united, there being at their point of junction a small ganglionic enlargement ; this arrangement has been denied by Lobstein and others.
3. External Carotid Plexus.— The external carotid plexus formed as already mentioned by the union of the nervi molles from the su perior cervical ganglion, commences at the origin of the external carotid artery. There is sometimes a gang,lionic enlargement present, which from the fact of being situated at the point of bifurcation of the common carotid artery, was termed by Arnold the intercaro tidean ganglion. The external carotid plexus extends along the artery of the same name, encircling it with numerous branches, on which frequently occur small ganglionic en largements. At its comraencement numerous communications are formed between it and the branches of the glosso-pharyngeal and vagus nerves, which go to form the pharyngeal plexus. It also forms connections with the upper cardiac nerve, and, higher up, as it passes with the artery through the parotid gland, branches are given off for the supply of this organ, and also others, which become connected with the facial and auriculo-tem poral nerves. Offsets are sent from it along the divisions of the external carotid artery, forming a number of plexuses around them, which are named according to the arterial branches which they accompany. One of these accompanies the superior thy roid artery into the substance of the thyroid gland : it communicates with the superior laryngeal and upper cardiac nerves. Another accompanies the ascending pharyngeal artery, and is inti mately connected with the phary ngeal plexus. The lingual plexus encircles the artery of the same name, giving off filaments to the sub lingual gland, and forming communications with the lingual branches of the glosso-pha ry ngeal nerve. The facial plexus surrounds the facial artery and its branches, one or two filaments, which accompany the submental artery, pass to the submaxillary gland, and communicate with the ganglion of the same name. Small plexuses accompanying the occi pital and posterior auricular arteries seem to terminate chiefly in the parotid gland. Most of the branches which accompany the super ficial temporal artery appear to pass along the arteries going to the ear and eyelids. Nu merous filaments, presenting here and there ganglionic enlargements, proceed upwards on the external carotid artery as far as its divi sion into the temporal and internal maxillary arteries ; many of these appear to terminate in the parotid gland, while others accompany the temporal and internal maxillary arteries. Of the latter, one is described by Arnold as emanating from the plexus surrounding the rniddle meningeal artery, and passing to the posterior part of the otic g-anglion. Subsidiary branches accompany the different divisions of the internal maxillary artery.
From the external carotid plexus several filaments pass downwards upon the cormnon carotid artery, forming, with others derived from the middle cervical ganglion, a plexus around the vessel, which accompanies it and forms communications with the inferior thyroid plexus, as well as with the superior cardiac nerve and cardiac plexus.
B. Thoracic Plexuses of the Sympathetic. — The plexuses occurring in the thorax in con nection svith the sympathetic are the cardiac plexus, and the plexus surrounding the thoracic aorta it also contributes to the formation of the pulmonary and ce.sophageal
plexuses.
1. Cardiac Plexus.— The cardiac plexus is formed by the union of the cardiac branches of the sympathetic already described, and by numerous filaments derived from the recurrent laryngeal, as well as from the vagus nerve it self; a branch from the descendens noni nerve accompanies the superior cardiac nerve, and also terminates in the plexus. The superior cardiac nerves, the branches from the recurrent laryngeal and vagus nerves terminate in the upper part of the plexus ; the middle cardiac branches of both sides terminate commonly in its middle portion, while the inferior cardiac branches, with some of those derived from the recurrent laryngeal nerve, end chiefly in its lower part. The plexus is asymmetrical, and is situated in the upper part of the tho racic cavity', extending from the transverse portion of the arch of the aorta to the base of the heart: it consists of a widely-meshed network of moderately fine filaments, some presenting a greyish, others a more or less svhite appearance. About the centre of the plexus, behind the arch of the aorta and in front of the bifurcations of the trachea, at the point of division of the pulmonary' artery there is commonly present a ganglionic en largement. This which is termed the cardiac ganglion (Ganglion cardiacum Wrisbergii), presents a greyish colour and irregular shape, generally more or less angular or oblong, and measures from one to two lines in length. That portion of the cardiac plexus which is formed by the branches of the sympathetic which pass down in front of the arteria in nominata on the right side, and the arch of the aorta on the left side, corresponds to what is termed by some the superficial cardiac plexus, while the portion formed by the branches of the sympathetic and vagus which descend behind the arch of the aorta between it and the trachea, is termed the deep cardiac plexus. The branches which proceed from the cardiac plexus are the following : —(a) Numerous filaments pass off from the upper part of the plexus and surround the arch of the aorta, as well as the large arterial trunks which spring froni the same., (b) Others pass along the right and left pulmonary arteries, and terminate in the pulmonary plexus. (c) Offsets are also sent along the coronary ar teries, forming the anterior and posterior coronary plexuses. The anterior coronary plexus is chiefly derived from the superficial portion of the cardiac plexus, and accom panies the anterior or right coronary artery and its divisions ; the posterior coronary plexus, chiefly derived from the left side of the deeper portion of the cardiac plexus, is situated at first behind the aorta and pulmo nary artery ; it then passes in front of the left division of the pulmonary artery to the base of the heart, and reaches the posterior co ronary artery, around which it forms an inter lacement of filaments. Numerous filaments are distributed by it to the left side of the heart, especially to the left ventricle : the filaments of the anterior coronary plexus are chiefly distributed to the right ventricle. The nerve filaments which leave the coronary plexuses do not all accompany the branches of the coronary arteries, as was formerly sup posed.; by far the greater nuniber of them run separately from the vessels, and are distributed to the muscular substance of the heart. As regards the arrangement of the nerves on leaving the coronary plexuses, they appear to be much more numerous on the ventricles than the auricles. The filaments distribut ed to the former are very numerous; they are directed from the base to the apex of the ventricle; those on the anterior surface passing obliquely downwards from left to right, those on the posterior surface from right to left ; they thus in general cross obliquely the direc tion of the muscular fibres of the ventricles, and often also that of the blood vessels. Where they cross the latter, especially in the heart of the young ox, they appear to bifur cate, so as to enclose the vessel in a loop ; and at this point there is frequently, as is re presented by Dr. Lee, a small enlargement which occasionally contains ganglionic matter.* In their course along the surface of the ven tricles, neighbouring filaments frequently unite, there being here also small ganglionic enlarge ments. According to Dr. Lee there are dis tinctly visible on the anterior surface of the young heifer's heart about ninety of these ganglia or ganglionic enlargements. The left ventricle appears to be moreabundantly sup plied with nerves than that of the right side : on the former they can be traced, extending from base to apex, on the surface of the latter they generally extend but a little way down, when they sink into the muscular substance.