532 THE CRANIAL XERYES. 



clinoid process. Continuing onwards throngh the enter wall of the 

 cavernous sinus, the fourth nerve enters the orbit by the sphenoidal 

 fissure, and above the muscles. Its position with reference to other 

 nerves in this part of its course has been already described. 



In the orbit, the fourth nerve inclines inwards above the muscles, and 

 enters finally the upper oblique muscle at its orbital surface. 



"While in its fibrous canal in the enter wall of the sinus, the fourth nerve is 

 joined by filaments of the sympathetic, and not imfrequently is blended with the 

 ophthalmic division of the fifth. Bidder states that three or more small fila- 

 ments of this nerve extend to the tentorium as far as the lateral sinus ; and has 

 figured one as joining- the sj-mpathetic on the carotid artery. (Neurologische 

 Beobachtungen, von F. H. Bidder. Dorpat, 1830.) 



FIFTH PAIR OF NERVES. 



The fifth, or trifacial nerve (nerv. trigeminus), the largest cranial 

 nerve, resembles a spinal nerve, in respect that it consists of a 

 motor and a sensory part, and that the sensory fibres pass through a 

 ganglion while the motor do not. Its sensory division, which is much 

 the larger, imparts common sensibility to the face and the fore part of 

 the head, as well as to the eye, the nose, the ear, and the mouth ; and 

 endows the fore part of the tongue with the powers of both touch and 

 taste. The motor root supplies chiefly the muscles of mastication. 



Surface attachment. — The nerve arises from the side of the pons 

 Varolii, where the transverse fibres of the latter are prolonged into the 

 middle crus cerebelli, considerably nearer to the upper than to the lower 

 border of the pons. The smaller root is at first concealed by the larger, 

 and is placed a little higher up, there being often two or three cross 

 fibres of the pons between them. On separating the two roots, the 

 lesser one is seen to consist of a very few funiculi. In the larger root 

 the funiculi are numerous, amounting sometimes to nearly a hundred. 



Beep origin. — The fibres of the large root pass backwards inwards 

 and slightly downwards as a compact bundle, towards the outer part of 

 the floor of the fourth ventricle. The chief nucleus, in which most of 

 the fibres end, is situated to the outer side of the trunk, and consists of 

 a collection of nerve cells, continuous below with the grey tubercle of 

 Rolando (caput cornu posterioris). The cells are small and arranged in 

 clusters, separated l)y the delicate fasciculi of origin of the nerve. In 

 front of this nucleus a number of descemlinri fibres pass down, mingled 

 with grey matter, to the lower part of tlie medulla oblongata. 



Some fibres of the nerve are said to join the middle peduncle of the 

 cerebellum ; others pass inwards beneath the floor of the fourth ven- 

 tricle, decussate at the raphe, and (according to Meynert) ascend on the 

 opposite side of the medulla. 



The small root passes in a curve, with the convexity forwards, to 

 reach the neighbourhood of the nucleus of the larger root. Its fibres 

 arise fi"om a group of large nerve cells, situated close to the outer angle 

 of the fourth ventricle, to the inner side of the fibres of the nerve. A 

 prolongation from this nucleus extends down the medulla, as far as the 

 olivary bodies, receding from the surface, and to it, below, some fib]-es 

 of origin of the facial nerve are traced. 



Course. — The roots of the fifth nerve, after emerging from the 

 surface of the encephalon, are directed forwards, side by side, to the 

 middle fossa of the skull, through a recess in the dura mater on the 



