546 CRANIAL NERYES. 



portion of the temporal bone ; here the fibres of the larger root enter a large 

 semilunar ganglion (Casserian), while the smaller root passes beneath the ganglion 

 without having any connection with it, and joins outside the cranium with one 

 of the trunks derived from it. 



The CASSERIAN or SEMILUNAR GANGLION is lodged in a depression near the 

 apex of the petrous portion of the temporal bone. It is of a somewhat crescentic 

 form, with its convexity turned forwards. Its upper surface is intimately adhe- 

 rent to the dura mater. 



Branches. This ganglion receives, on its inner side, filaments from the carotid 

 plexus of the sympathetic ; and from it some minute branches are given off to the ten- 

 torium cerebelli, and the dura mater, in the middle fossa of the cranium. From 

 its anterior border, which is directed forwards and outwards, three large branches 

 proceed ; the ophthalmic, superior maxillary, and inferior maxillary. The two 

 first divisions of this nerve consist exclusively of fibres derived from the larger 

 root and ganglion, and are solely nerves of "common sensation. The third or 

 inferior maxillary is composed of fibres from both roots. This, therefore, strictly 

 speaking, is the only portion of the fifth nerve which can be said to resemble a 

 spinal nerve. 



BRANCHES OF THE FIFTH NERVE. 

 (1.) OPHTHALMIC NERVE. 



The OPHTHALMIC, the first division of the fifth, is a sensory nerve. It supplies 

 the eyeball, the lachrymal gland, the mucous lining of the eye and nose, and the 

 integument and muscles of the eyebrow and forehead (fig. 275). It is the smallest 

 of the three divisions of the fifth, arising from the upper part of the Casserian 

 ganglion. It is a short, flattened band, about an inch in length, which passes for- 

 wards along the outer wall of the cavernous sinus, below the other nerves, and 

 just before entering the orbit, through the sphenoidal fissure, divides into three 

 branches, frontal, lachrymal, and nasal. The ophthalmic nerve is joined by fila- 

 ments from the cavernous plexus of the sympathetic, and gives off recurrent 

 filaments which pass between the layers of the tentorium, with a branch from the 

 fourth nerve. 



Its branches are the 



Lachrymal. Frontal. Nasal. 



The Lachrymal is the smallest of the three branches of the ophthalmic. Not 

 unfrequently it arises by two filaments, one from the ophthalmic, the other from 

 the fourth, and this, Swan considers, as the usual condition. It passes forwards 

 in a separate tube of dura mater, and enters the orbit through the narrowest part 

 of the sphenoidal fissure. In this cavity, it runs along the upper border of the 

 External rectus muscle, with the lachrymal artery, and is connected with the 

 orbital branch of the superior maxillary nerve. Within the lachrymal gland it 

 gives off several filaments, which supply it and the conjunctiva. Finally it pierces 

 the palpebral ligament, and terminates in the integument of the upper eyelid, 

 joining with filaments of the facial nerve. 



The Frontal is the largest division of the ophthalmic, and may be regarded, both 

 from its size and direction, as the continuation of this nerve. It enters the orbit 

 above the muscles, through the highest and broadest part of the sphenoidal fissure, 

 and runs forwards along the middle line, between the Levator palpebros and the 

 periosteum. Midway between the apex and base of this cavity, it divides into 

 two branches, supra-trochlear and supra-orbital. 



The supra-trochlear branch, the smaller of the two. passes inwards, above the 

 pulley of the Superior oblique muscle, and gives off a descending filament, which 

 joins with the infra-trochlear branch of the nasal nerve. It then escapes from 

 the orbit between the pulley of the Superior oblique and the supra-orbital foramen, 

 curves up on to the forehead close to the bone, and ascends behind the Corru gator 

 supercilii and Occipito-frontalis muscles, to both of which it is distributed 

 finally, it is lost in the integument of the forehead. 



