The nasal nerve is described as giving also, in some instances, but not uniformly, a branch to the membrane of the superior turbinate bone, at the superior part of the nostril.
3. The third branch of the first division of the fifth is the lachrymal: it has been so called by Winslow from its distribution to the lachrymal gland : it is the smallest of the three branches : its course is external to that of the others, and hence it is also called the external branch. It arises, for the most part, from the ophthalmic at the same time with its other branches ; J. F. Meckel asserts that it arises more fre quently from a trunk common to it and the frontal ; but the contrary is maintained by the elder Meckel; he, however, states that it arises frequently by two roots, one from the ophthalmic, and a second from the frontal, and once lie has seen it derive a root from the tern poro-malar branch of the superior maxillary nerve.* When it arises from the ophthalmic, it is at its origin, inferior to the frontal, and exter nal to the nasal. Its course is forward and outward at a very acute angle with the frontal ; it enters the orbit through the foramen lacerum, and from its origin until its entrance it is con tained in the dura mater lining the inner side of the middle fossa of the hase of the cranium, beneath the lesser wing of the sphenoid bone : in entering it passes above the origins of the external rectus muscle, between it and the pe riosteum, and pursues its course along the outer wall of the orbit, external to the superior rectus and superior to the external, until it reaches the lachrymal gland : it then passes between the gland and the eyeball, and then divides into branches. It is accompanied through its course by the lachrymal artery. The branches into which it divides are, for the most part, three ; they enter the gland on its ocular surface, traverse it and again escape from it on its external aspect ; in their course through the gland they divide and commu nicate with each other, and thus form within it a plexus, from which numerous ramifications are distributed to its substance. After having supplied the gland the branches of the lachry mal emerge from it, and pursue two destina tions : one of them, which is for the most part the first branch of the nerve, and is frequently given off before it has reached the gland, de scends backward toward the spheno-maxillary cleft, and joins the temporal branch of the temporo-malar branch of the second division of the fifth. In its course this branch passes first between the external rectus muscle and the outer wall of the orbit, then becomes attached to the wall, and is either simply inclosed in the periosteum, or contained in a groove or canal in the orbitar process of the malar, or some times of the sphenoid bone; in this canal it meets the branch of the temporo-malar, and from the junction of the two results a filament, the des tination of which will be described under that of the temporo-malar. This branch of the
lachrymal nerve is called the posterior or sphe no-maxillary : it might from its destination be appropriately termed temporal: it frequently gives off in its descent a filament, which passes forward, escapes from the orbit beneath the ex ternal canthus, and is distributed as the other branches of the lachrymal are. The remaining branches of the lachrymal escape from the orbit into the upper eyelid, beneath the exter nal part of the superciliary arch. They give off numerous filaments, which are distributed to the structures of the lid, the conjunctiva, the orbicular muscle, and the integument : the ex ternal of them, which are the largest, not only supply branches to the upper, but descend be hind the external commissure of the lids into the lower one, which they supply at its outer part ; they are also distributed to the superfi cial parts on the malar region. They anasto mose with the frontal nerve, the superficial temporal, the facial, the temporo-malar, and the infra-orbital nerves.
The second division of the fifth.—This has been called also by Winslow, in consequence of its distribution, the superior maxillary nerve. It is the second trunk connected with the Gasserian ganglion, and is intermediate to the others, both in size and situation ; larger than the first, and placed beneath and external to it; smaller than the third, and situate internal, superior and anterior to it ; it is attached to the middle of the anterior convex margin of the ganglion ; at first it is flattened, wide, and of a cineritious tint ; but, as it proceeds, it becomes contracted in width, of a cylindrical form, and presents a white colour. At leaving the gan glion it is joined by a filament of the sympa thetic. This has been seen by Munniks* and Laumonier,-1- and is stated by Meckel junior, on the authority of the latter. The communi cation between the sympathetic and the second and third divisions is called in question by Arnold.: That with the third the author has not yet made out, but that with the second he has found satisfactorily established by a fila ment from the branch of the sympathetic which joins the sixth nerve : this filament connects the sixth to the second division of the fifth, and is short, but grosser than those which join the first: in consequence of the irregularity which pre vails in the arrangement of the sympathetic system, the description here given may not apply in other instances.