It is said that the nerve may be held to arise from this tract, because, though it be certainly not its ultimate connection with the brain, and though cords can be traced from it to more remote parts, yet the union of the cords at the point, and the attachment of both portions of the nerve to it, seem to mark it as the origin of the nerve ; the change of character too which will be described as occurring at the attach ment of the nerve, countenances the opinion that the tract is not simply a continuation of the nerve.
It may be doubted whether the eminence really exist, or whether it be not merely the result of dissection : the author will not insist upon it, but several considerations induce him to consider it real : in the first place, he almost uniformly finds it,* and secondly, it seems to be a common point to the two portions of the nerve and to the other cords, which form part of its encephalic connections ; and lastly, this view is corroborated by the disposition of the same part in other animals ; for a similar ap pearance will be found, at the attachment of the nerve behind the pons, in other mammalia as well as in man after the separation of the adjoining matter, e.g. in the horse; and it is even asserted by Desmoulins that an eminence may be observed naturally upon the floor of the fourth ventricle, in some animals, at the attachment of the nerve. his statement is : " on observe meme dans les rongeurs, les taupes, et les herissons, un petit mamelon ou tubercle sur l'extremite ant6rieure du bord du ventricule ; mamelon, dans lequel se continuent les fibres posterieures de la cinquime paire, et de l'acoustique." When the tract has reached the point at which the inferior peduncle of the cerebellum first inclines outward toward the hemisphere, it separates, as has been stated, into two parts or cords, (seefigs. 140, 141,) destined, one, as is already known, to the posterior, the other, according to the author's belief, to the an terior column of the spinal cord. The course and disposition of these cords are remarkable and apparently contrary to analogy ; they are dis tinguishable into anterior and posterior, but they descend, the anterior to the posterior, and the posterior to the anterior columns. The an terior cord is by much the larger, and is pro longed through the inferior peduncle of the cerebellum, until at the inferior extremity of the bulb it is continued into the longitudinal fasciculi of the corresponding posterior column of the spinal marrow ; it is situate along the outer side of the olivary body, but separated from it by a slight interval, nor does it seem to have any connection with that body : it is imbedded in the substance of the superior part of the peduncle, situate, however, nearer to its anterior than its posterior surface, and laid obliquely across its fibres as they pass outward toward the hemisphere of the cerebellum; but as it proceeds it becomes gradually more super ficial, gains the outer side of the peduncle, and at the lower extremity of the bulb is actually at its surface almost immediately behind the lateral fissure of the cord and the posterior roots of the superior cervical nerves. The existence and
course of this cord have been first established and described by Rolando in his "Saggio sopra la vera Struttura del Cervello," and also in a memoir upon the Anatomy of the Medulla oblongata, published in the fourth volume of the Journal of Physiology.
The posterior cord is much smaller than the former ; it descends behind the inferior pedun cle of the cerebellum, as it passes outward into the hemisphere, and upon the posterior aspect of the spinal bulb ; enters the posterior fissure of the bulb, between the posterior py ramids, and can be traced some way down ward, in the bottom of the fissure, along the back of the anterior column of the same side, into which it appears to be ultimately con tinued. ( Figs. 140, 141, 13.) The preceding account of the encephalic connections of the fifth nerve differs very much from that adopted by some of the highest modern authorities. It is not necessary to allude to the opinions entertained upon the point, before the course of the nerve had been particularly inquired into ; but, accord ing to some of the most recent, the nerve arises from the groove between the restiform and olivary bodies, and from the olivary bodies themselves. Such is the view given of the origin of the nerve by Gall and Spurzheim in their fifth plate of the brain, in which the nerve is represented breaking up, on the out side of the olivary body, into several fasciculi, which plunge obliquely into it. In their account* of the course of the nerve into the brain they state," on peut aisetnent suivre son cams entier jusq'au dessous du cote exterieur des corps olivaires ;" this might be, perhaps, interpreted to mean beyond the °liveries, reference being had to the relations of those bodies in the erect posture ; but from the representation given it is obvious that the in tended meaning is, that the nerve can be fol lowed to beneath, i. e. underneath, their outer side, the brain being placed in the manner ordinarily adopted for dissection, in which the anterior aspect of the olivarics is rendered superior ; indeed their representation is alto gether incompatible with the opinion that they had traced the nerve beyond the bodies.