616 CRAXIAL NER7ES. 



mater, at the apex of the petrous 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 

 adherent 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 tentorium 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 ophthalmic and superior maxillary consist exclusively of fibres derived 

 from the larger root and ganglion, and are solely nerves of common sensation. 

 The third division, 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. 



OPHTHALMIC NERVE. (Fig. 339.) 



The Ophthalmic, or 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. 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 

 forwards 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, lachrymal, frontal, and nasal. The ophthalmic nerve is joined 

 by filaments from the cavernous plexus of the sympathetic, and gives off recur- 

 rent 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 to be its 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 the orbit, it runs along the 

 upper border of the External Eectus 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 the gland 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 sphe- 

 noidal fissure, and runs forwards along the middle line, between the Levator 

 palpebroo and the periosteum. Midway between the apex and base of the orbit 

 it divides into two branches, supratrochlear and supraorbital. 



The supratrochlear branch, the smaller of the two, passes inwards, above the 

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

 \vhichjoins with the infratrochlear branch of the nasal nerve. It then escapes 

 from the orbit between the pulley of the Superior Oblique and the supraorbital 

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

 the Corrugator Supercilii, and Occipito-frontalis muscles, to both of which it is 

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



