280 



FIFTH PAIR OF NERVES. 



closely attached to the fourth nerve, but pre- 

 sently after separates from it, the fourth in- 

 clining inward, is continued forward to the 

 superciliary foramen, lying upon the superior 

 surface of the superior rectus and levator palpe- 

 brae muscles, being through its whole course 

 within the orbit immediately beneath its roof. 

 Having reached the foramen it passes through 

 it, and changing its direction, ascends round 

 the superciliary arch, upon the forehead, be- 

 neath the orbicularis palpebrarum and frontalis 

 muscles, and is thenceforth called by some the 

 external frontal nerve in contradistinction to a 

 branch from itself, the supra-trochlear,or internal 

 frontal. In its mode of escape from the orbit 

 the frontal nerve is subject to some variety, 

 consequent in part upon the mode in which 

 the superciliary foramen is formed, that being 

 in some instances altogether osseous, in others 

 osseous only at its superior part and completed 

 by ligament below; in this case the nerve 

 escapes through an osseous notch, and not a 

 foramen. In other instances, again, when the 

 nerve divides previous to its escape it is some- 

 times transmitted through two apertures. 



The distribution of the frontal nerve, as well 

 as that of most of the secondary branches, is 

 subject to varieties, which the author has en- 

 deavoured to embrace in the following account. 

 In the first place the frontal, at its entrance 

 into the orbit, anastomoses with the fourth 

 nerve. Next it gives off, some time after its 

 entrance and previous to its division, a long and 

 slender branch, which runs forward and inward 

 toward the trochlea of the superior oblique. 

 Then it divides into two branches, a larger 

 one, the continuation of the nerve, which 

 escapes through the superciliary foramen, and 

 a smaller, the supra-trochlear or internal 

 frontal. The latter passes forward and at the 

 same time inward toward the trochlea of the 

 oblique muscle, escapes from the orbit internal 

 to the continued trunk of the frontal nerve, 

 and ascending upon the forehead beneath the 

 corrugator supercilii, orbicularis, and frontalis 

 muscles, it has received the name of internal 

 frontal, in contradistinction to the continued 

 trunk, which is at the same time called external 

 frontal. The point at which the frontal divides 

 is variable; for the most part the division takes 

 place about midway in the orbit. In some 

 instances it occurs before the nerve has reached 

 that point, and in others, again, not until it 

 has approached nearer to the anterior margin of 

 the orbit. The distance of the division from 

 the margin of the orbit appears to modify the 

 course of the internal branch : when it is far 

 back, the nerve escapes from the orbit above 

 the trochlea, and hence the name supra-tro- 

 chlear, given to it by Meckel ; and when near the 

 margin it escapes external to the trochlea, be- 

 tween it and the superciliary foramen ; while in 

 the latter case a branch of the nerve is transmitted 

 above the trochlea, in the usual course of the 

 nerve itself. Nor is the size of the two branches 

 into which the frontal divides equal or uni- 

 form ; for the most part the external branch is 

 the larger, but in some instances the two are 

 of equal size. In its course forward the supra- 



trochlear nerve gives off first, occasionally a 

 delicate branch, which frequently arises from 

 the frontal itself prior to its division, the course 

 and destination of which have been already 

 described. Next it gives off, in some instances 

 before, in others not till after it has escaped 

 from the orbit, a branch which passes inward 

 toward the internal canthus, and, uniting with 

 either the infra-trochlear itself or a branch of 

 it, concurs in forming a small plexus, from 

 which filaments are distributed to the structures 

 of the upper eyelid, toward its internal part, 

 and to the eyebrow. Having escaped from 

 the orbit, the supra-trochlear nerve divides into 

 two sets of branches, denominated pulpcbral 

 and frontal ; the first descend into the superior 

 eyelid, and are distributed to the structures of 

 that part ; the filaments communicating exter- 

 nally with those of the frontal, and internally 

 with those of the infra-trochlear. The frontal 

 branches ascend round the superciliary arch, 

 beneath the orbicularis palpebrarum and the 

 corrugator supercilii muscles, upon the fore- 

 head, and these are disposed of in a manner 

 similar to that in which the branches of the 

 proper or external frontal are. Some are dis- 

 tributed to the orbicularis, corrugator, and fron- 

 talis muscles; other, long branches, ascend 

 beneath the frontalis, traverse it, and become 

 subcutaneous, and are distributed to the inte- 

 guments of the scalp upon the forehead. Of 

 these the external unites with the internal 

 branch of the external frontal, and forms with 

 it a common branch, which has the same 

 destination as the others. 



The external larger branch of the frontal, 

 called, in contrast with the last, the external 

 frontal nerve, also divides into two sets of 

 branches, palpebral and frontal. 



The nerve in some instances emerges from 

 the orbit a single trunk, in others it divides be- 

 fore it escapes from that region, for the most 

 part into two branches, which are transmitted 

 sometimes through the same, at others through 

 distinct apertures, and from which the several 

 ramifications arise, they themselves becoming 

 ultimately the long frontal branches. 



Immediately after their escape the frontal 

 branches give off externally slender filaments, 

 which run outward toward the external can- 

 thus, one beneath the eyebrow, through the 

 upper eyelid, and one or more through the 

 brow itself; these ramify as they proceed, sup- 

 ply the lid and brow at their outer part, and 

 anastomose with filaments of the portio dura, 

 and of the superficial temporal nerve. 



The frontal branches are arranged into super- 

 ficial and deep ; those epithets have been diffe- 

 rently applied by different writers ; thus those 

 which the elder Meckel terms the superficial, 

 Boyer and Cloquet denominate the deep 

 branches ; nor is this to be wondered at, inas- 

 much as both sets become ultimately superficial; 

 it were better, perhaps, to arrange them into 

 short and long branches. The short branches 

 are distributed to the orbicularis muscle, the 

 corrugator, and the frontalis, and having sup- 

 plied those muscles, they or others of them be- 

 come subcutaneous, and terminate in the inte- 



