396 



TRIFACIAL. 



Fig - 179 * fifth nerve, and passes along the outer 



wall of the cavernous sinus to the 

 sphenoidal fissure. In its course 

 through the sinus it is situated at first 

 below the motor oculi, but afterwards 

 ascends and becomes the highest of 

 the nerves which enter the orbit 

 through the sphenoidal fissure. Upon 

 entering the orbit the nerve crosses 

 the levator palpebrae muscle near its 

 origin, and is distributed upon the 

 orbital surface of the superior oblique 

 or trochlearis muscle ; hence its syno- 

 nyn trochlearis. 



Branches. While in the cavernous 

 sinus the fourth nerve gives off a re- 

 current branch, some filaments of communication to the ophthalmic nerve, 

 and a branch to assist in forming the lachrymal nerve ; the recurrent branch, 

 which consists of sympathetic filaments derived from the carotid plexus, 

 passes backwards between the layers of the tentorium, and divides into 

 two or three filaments, which are distributed to the lining membrane of 

 the lateral sinus. This nerve is sometimes a branch of the ophthalmic, 

 and occasionally proceeds directly from the carotid plexus. 



FIFTH PAIR. TRIFACIAL (trigeminus). The fifth nerve, the great sen- 

 sitive nerve of the head and face, and the largest cranial nerve, is analogous 

 to the spinal nerves in its origin by two roots, from the anterior and pos- 

 terior columns of the spinal cord, and in the existence of a ganglion on 

 the posterior columns of the spinal cord, and in the existence of a ganglion 

 on the posterior root. It arisesf from a tract of yellowish-white matter 

 situated in front of the floor of the fourth ventricle and the origin of the 

 auditory nerve, and behind the crus cerebelli. This tract divides inferiorly 

 into two fasciculi which may be traced downwards into the spinal cord, 

 one being continuous with the fibres of the anterior column, the other with 

 the posterior column. Proceeding from this origin the two roots of the nerve 

 pass forward, and issue from the brain upon the anterior part of the crus 

 cerebelli, where they are separated by a slight interval. The anterior is 

 much smaller than the posterior, and the two together constitute the fifth 

 nerve, which in this situation consists of seventy to a hundred filaments held 

 together by pia mater. The nerve then passes through an oval opening in 

 the border of the tentorium, near the extremity of the petrous bone, and 

 spreads out into a large semilunar ganglion, the Casserian. If the ganglion 

 be turned over, it will be seen that the anterior root lies against its under 



* A view of the 3d, 4th, and 6th pairs of nerves. 1. Ball of the eye, the rectus exter- 

 nus muscle being cut and hanging down from its origin. 2. The superior maxilla. 3. 

 The third pair or motor oculi distributed to all the muscles of the eye except the pupe- 

 rior oblique and external rectus. 4. The 4th pair or patheticus going to the superior 

 oblique muscle. 5. One of the branches of the 5th. 6. The 6th pair cr motor extcrtius 

 distributed to the external rectus muscle. 7. Spheno-palatine ganglion and branches. 

 8. Ciliary nerves from the lenticular ganglion, the short root of which is seen to connect 

 it wi*h the 3d pair. 



fl have adopted the origin of this nerve, given by Dr. Alcock, of Dublin, as the result 

 of his directions, in the Cyclopaedia of Anatomy and Physiology. Mr. Mayo also traces 

 ilia an.erior root of the nerve to a similar origin. 



