FIFTH PAIR OF NERVES. 



279 



internal to the other two, the second is inferior 

 and external to the first, and the third is exter- 

 nal, posterior, and inferior to both the others. 

 They go off from the ganglion at different 

 inclinations, the first forward and slightly 

 upward, the second directly forward, and the 

 third almost directly downward; hence the 

 first and second form a very acute angle with 

 each other, while that between the second and 

 third is much greater. 



First or ophthalmic division. This division 

 is distributed to the eye and its appendages, 

 to the nostril, and to the forehead. It is the 

 smallest of the three trunks proceeding from 

 the ganglion, and is situate superior and inter- 

 nal to the other two. It is about three-fourths 

 of an inch long from the ganglion to its division 

 into branches, and is contained thus far within 

 the cranium. Its course is forward, upward, 

 and slightly outward toward the upper part of 

 the foramen lacerum of the orbit. It is laid 

 against the outer side of the cavernous sinus, 

 in company with the third and fourth nerves, 

 and is contained in the external wall of the 

 sinus, being separated from the interior of that 

 chamber by a thin septum, which is a prolon- 

 gation of the inferior internal wall of the canal 

 in which the nerve and ganglion are contained. 

 The septum is dense, but at the same time so 

 thin and transparent that the nerve can be seen 

 through it from the side of the sinus, while the 

 lamina of the dura mater, by which it is sepa- 

 rated from the interior of the cranium, is so 

 thick and opaque, that the course of the nerve 

 is altogether concealed from that side. At its 

 outset the nerve is beneath, and external to the 

 third and fourth nerves, and external and some- 

 what superior to the sixth, which is within the 

 sinus; but ascending as it proceeds, it gains, 

 about the middle of the sinus, the same level 

 with the third, placed still at its outer side, 

 and inferior to the fourth, and then terminates 

 by dividing into branches. 



Presently after its origin from the ganglion 

 the nerve is joined by one or more very fine 

 filaments from the sympathetic: this is ex- 

 pressly denied by the first Meckel, but he was 

 certainly mistaken; they are very faithfully 

 represented by Arnold. In order to display 

 them the sixth nerve may be separated carefully 

 from the carotid artery in the cavernous sinus, 

 after which it will be found that branches of 

 the sympathetic ascend upon the artery internal 

 to that nerve, and distinct from those which 

 are connected with it. Having surmounted it 

 they branch off, some upon the artery as it 

 passes to the brain, others to other destinations, 

 and of the latter some incline outward above 

 the sixth nerve and are connected to the first 

 division of the fifth : they are short and very 

 delicate. 



The first division of the fifth gives off no 

 branch from its outset to its final division, 

 except an extraordinary filament described by 

 Arnold, and denominated by him the recurrent 

 branch of thefrst division of the fifth . It arises 

 from the upper side of the trunk immediately 

 after it leaves the ganglion^ runs backward above 

 this body at a very acute angle, enters the struc- 



ture of the teutorium cerebelli, and divides be- 

 tween its laminae into several very delicate fila- 

 ments. 



The branches into which the first division of 

 the fifth ultimately divides are either two or three; 

 according to the elder Meckel and the greater 

 number of authorities they are three ; according 

 to others they are sometimes three, but are more 

 frequently only two. The three branches are 

 the frontal, the nasal, and the lachrymal. 

 When the branches are but two, they are, 

 according to J. F. Meckel, the nasal and the 

 frontal, the latter in such case giving off that, 

 which in the other mode of distribution is the 

 third, the lachrymal. The elder Meckel attributes 

 the difference of opinion which prevails with re- 

 gard to this point to the fact that the lachrymal 

 nerve frequently has a second root derived 

 from the frontal, which in such cases has been 

 assumed to be the origin of the nerve. The 

 names which have been applied to those 

 branches have been taken either from their 

 destination or from their relative course ; thus 

 the frontal, so called from its distribution to 

 the forehead, is also called the superior or 

 middle branch; the nasal, so called because 

 finally distributed to the nostril, the internal 

 or inferior, and the lachrymal, which derives 

 its name from the lachrymal gland, the external. 

 The three branches differ in size ; the frontal is 

 considerably larger than either of the others, 

 the nasal is second, and the lachrymal is much 

 the smallest. They all three traverse the orbit, 

 but they pursue different routes, and have, at 

 entering, very different relations. 



1. The frontal nerve appears in the human 

 subject, both from its size and its direction, to be 

 the continuation of the original trunk. In other 

 animals, however, it is otherwise : in them the 

 predominance of the frontal nerve diminishes 

 along with that of the superior region of the 

 face, until in some it ceases to exist as a pri- 

 mary branch of the first division of the fifth, 

 and its place is supplied by a secondary branch 

 of another, while the nasal branch increases 

 in the same proportion, and seems ultimately 

 to constitute itself the first division of the fifth.* 

 The frontal nerve passes upward and forward 

 toward the highest part of the foramen lacerum 

 of the orbit, and enters that region through it. 

 It then continues its course through the orbit 

 to the superciliary foramen and escapes through 

 it to the forehead. During this course it is 

 placed, before it has entered the orbit, at the 

 outer side of the third nerve; it then rises 

 above the third and crosses over it to its inner 

 side. In doing so it is accompanied by the 

 fourth nerve, to which it is external and in- 

 ferior; it enters the orbit in company with 

 the fourth and nearly on the same level, but 

 still external to and somewhat beneath it. In 

 entering, it passes above the origin of the 

 superior rectus muscle, and all the other parts 

 transmitted through the foramen lacerum, with 

 the exception of the fourth nerve. At the en- 

 trance of the frontal nerve into the orbit and 

 during its course from its origin thereto it is 



* See comparative distribution of the fifth ucivc. 



