236 THE CRANIAL NERVES. 



Frontal nerve. The frontal nerve (fig. 152, 4), the largest division of the 

 ophthalmic, also enters the orbit above the muscles, and runs forwards between the 

 elevator of the upper eyelid and the periosteum. About the middle of the orbit it 

 divides into two branches, supratrochlear and supraorbital. 



(a) The supratrochlear nerve, much the smaller of the two branches, inclines 

 inwards towards the pulley of the superior oblique muscle, close to which it sends a 

 filament downwards to communicate in a loop with the infratrochlear branch of the 

 nasal nerve, and then leaves the orbit between the orbicularis palpebrarum muscle 

 and the bone. In this position the nerve gives twigs to the skin and conjunctiva 

 of the upper eyelid, and finally it turns upwards, dividing into branches which per- 

 forate the orbicularis and frontalis muscles, and are distributed to the integument 

 of the lower and mesial part of the forehead. 



(b) The supraorbital nerve is the continuation of the frontal nerve, and leaves 

 the orbit by the supraorbital notch or foramen. It divides into two branches, inner 

 and outer, w r hich ascend on the forehead beneath the frontalis muscle, and are dis- 

 tributed by numerous slender ramifications to the skin of the fore and upper parts 

 of the scalp. The outer branch is the larger, and extends backwards nearly to the 

 lambdoid suture ; the inner branch reaches but a little way over the parietal bone. 

 In the supraorbital notch a slender filament of the nerve enters an aperture in the 

 frontal bone, where it is said to be distributed to the diploe and the mucous lining 

 of the frontal sinus ; as the nerve emerges from the orbit, twigs are sent downwards 

 to the upper eyelid ; and from its terminal divisions small branches pass to the 

 pericranium. 



The primary division of the supraorbital nerve often takes place before it issues 

 from the orbit, and in that case only the larger branch passes through the supra- 

 orbital notch, the smaller one being placed more internally, and not unfrequently 

 traversing a second slighter notch (frontal notch, Henle) in the orbital margin 

 (fig. 152, 5, 6). 



The branches of the supraorbital nerve, and the same is the case with all the 

 cutaneous offsets of the fifth, form communications with the adjacent ramifications 

 of the facial nerve ; in this way sensory fibres derived from the fifth nerve may be 

 conveyed to the surrounding muscles. 



Nasal nerve. The nasal nerve (oculo-nasal or naso-ciliary} enters the orbit 

 between the heads of the external rectus muscle, and between the two divisions of 

 the third nerve. It then inclines inwards over the optic nerve, passing beneath the 

 superior rectus and superior oblique muscles, to the inner side of the orbit, and 

 leaves that cavity by the anterior internal orbital canal. In this part of its course 

 it furnishes a slender branch to the ciliary ganglion, one or two filaments (long 

 ciliary) directly to the eyeball, and a considerable infratrochlear branch, which arises 

 just before the nerve enters its canal on the inner side of the orbit. 



Arrived in the cranial cavity, the nerve is directed forwards in a groove at the 

 outer edge of the cribriform plate of the ethmoid bone to a small canal between the 

 fore part of the plate and the frontal bone, through which it descends to the nasal 

 fossa. Here it gives off internal or septal and external branches to the mucous 

 membrane of the fore part of the nasal fossa, and is then continued downwards in 

 the groove on the back of the nasal bone, to terminate as the anterior or. superficial 

 branch in the integument of the lower part of the nose. 



(a) The branch to the ciliary ganglion, very slender, and from a quarter to 

 half an inch in length, arises generally between the heads of the external rectus. It 

 lies on the outer side of the optic nerve, and enters the upper and back part of the 

 ganglion, constituting its long root. 



(b) The long ciliary nerves are situated on the inner side of the optic nerve ; 



