278 



FIFTH PAIR OF NERVES. 



and also beneath the superior petrous sinus : 

 by this aperture the chamber communicates 

 with the cerebral cavity and the nerve enters. 

 The chamber is lined by the arachnoid mem- 

 brane, as far as the posterior margin of the gan- 

 glion, but along this the membrane is reflected 

 from the interior of the chamber to the nerve, 

 and returns upon it into the cranium: hence 

 the nerve is free within the chamber, while 

 the dura mater is attached to the surfaces of 

 the ganglion, and so closely that it requires 

 care to separate it from them. The cham- 

 ber presents a remarkable variety in its con- 

 struction in some animals: in the horse, for 

 instance, its parietes are not simply fibrous, 

 as in man, but, frequently at least, in great 

 part ossecus, being at the same time lined by 

 the membrane. 



The passage of the nerve over the margin 

 of the petrous bone is marked by an inter- 

 ruption in the sharp edge, which the bone 

 presents external to that point, and its site 

 upon its anterior surface, as also that of the 

 ganglion by a corresponding shallow depres- 

 sion. 



Throughout the course of this portion of 

 the nerve, the relation of the two packets 

 to each other varies ; at the attachment of the 

 nerve to the crus cerebelli, the smaller packet, 

 allowance being made for those varieties pre- 

 sented by it in its mode of attachment, is 

 superior and internal to the larger ; in the in- 

 terval between the crus and the margin of the 

 petrous bone, the smaller packet gradually 

 descends along the inner side of the larger, 

 until it has reached the same level, so that the 

 two packets are placed immediately side by 

 side upon the margin of the bone, the lesser 

 internal to the greater ; but as the nerve pro- 

 ceeds into the middle fossa, the smaller, at 

 the same time, passes from within outward 

 beneath the larger, and also beneath the gan- 

 glion, toward its outer and posterior extremity; 

 during this course it has no communication 

 with the ganglion, but is quite distinct from 

 it, though inclosed in common in the chamber 

 formed by the dura mater, and connected with 

 it by a dense cellular or fibrous structure; but 

 having thus passed the ganglion, the lesser 

 packet is united to the third trunk proceeding 

 from that body, and with it constitutes the third 

 division of the nerve. 



The larger packet, on the contrary, is at- 

 tached to the ganglion. It has been before 

 stated that the plexiform arrangement, which 

 it presents, becomes less, as it approaches that 

 body; its fasciculi become more distinct; they 

 separate from each other, so that the width of 

 the packet is greatly increased, and having 

 reached the posterior margin of the ganglion 

 they are received into the channel which it 

 presents ; in which they are ranged, in series, 

 from one extremity of the body to the other, 

 overlapped by its edges, and enter abruptly into 

 the substance of the ganglion. 



External portion of the nerve. The external 

 orperipheric portion of the nerve consists of three 

 large trunks or divisions, which are connected, 

 on the one hand by their ramifications, with the 



organs to which the nerve is distributed, and 

 on the other, with the ganglion and the brain. 

 They are distributed, generally speaking, to 

 three different regions of the head and face, 

 one to the uppermost, another to the middle 

 or superior maxillary, and the third to the 

 lowest or inferior maxillary regions, and they 

 are denominated, either numerically, first, 

 second, and third, as by the first Meckel; or, 

 according to the parts to which they are dis- 

 tributed, the first the ophthalmic, by Willis; 

 the second the superior maxillary, and the 

 third the inferior maxillary, by Winslow. 

 These methods of distinction have their several 

 advantages. Could we select names which 

 would give adequate ideas of the distribution 

 of the "trunks, the latter would certainly be 

 preferable; but inasmuch as those which have 

 been selected do not at all adequately express 

 that distribution, and are attended, therefore, 

 with the inconvenience of not giving a suffi- 

 ciently enlarged idea thereof, it would probably 

 have been better, had the former been from 

 the first adopted and adhered to, for such 

 names could not create any incorrect impression 

 with regard to the distribution of the several 

 divisions of the nerve; in fact, the epithets 

 ophthalmic, superior, and inferior maxillaries 

 ought to be altogether discarded, for, beside 

 the objection to their use already stated, it will 

 be found, upon reference to the anatomy of 

 other animals, that they are by no means dis- 

 tinctly appropriate, and that the circumstances 

 upon which they are founded are purely inci- 

 dental, associated with the peculiarities of the 

 animal ; for the proof of which, see the com- 

 parative disposition of the fifth nerve in the 

 several classes. 



The three trunks differ from each other in 

 size. The first, the ophthalmic, is the smallest; 

 the second, the superior maxillary, is inter- 

 mediate in size; and the third, the inferior 

 maxillary, is by much the largest. They are 

 connected to the anterior convex margin of the 

 ganglion, the first to its superior internal 

 extremity, the second to its middle, and the 

 third to its inferior external extremity. At their 

 attachment they are wide, flattened, and of a 

 cineritious tint; but as they proceed they 

 become contracted in width, cylindrical or oval 

 in form, and of a white colour. Their texture 

 is fascicular and compact, the fasciculi of which 

 they are composed being bound up closely 

 together, and they differ remarkably in com- 

 position, the two first, the ophthalmic and 

 superior maxillary, being derived altogether 

 from the ganglion, and thus being, in anato- 

 mical constitution, simple ; whereas the third 

 is composed of two parts, one derived from 

 the ganglion, and another formed by the lesser 

 packet of the nerve, which does not join that 

 body, and hence that division is compound. 



The trunks rest partly against the outer side 

 of the cavernous sinus and in part upon the 

 base of the cranium in its middle fossa, and 

 they are enclosed in offsets from the fibrous 

 chamber, in which the ganglion is contained. 

 Their relative position corresponds to the posi- 

 tion of the ganglion; the' first is superior and 



