The external branch runs in the substance of the lower eyelid, distributing branches in its course, to the outer canthus, where it anasto moses with the inferior palpebral filaments of the lacrymal nerve.
The internal branch supplies the part of the lower eyelid towards the nose, and terminates in the parts at the inner canthus, anastomosing with a branch of the infra-trochlear.
The facial or portio dura of the seventh pair. —Of the accessory parts of the eye, the orbi cularis muscle is that which receives branches from the portio dura of the seventh pair; per haps, also, the tensor tarsi muscle, as Mac kenzie conjectures. These branches of the portio dura freely anastomose with the branches of the fifth pair above described.
To this superficial notice of the nerves of the accessory parts of the eye described in this article, all that requires to be added is, that the levator palpebrw superioris receives its nervous filaments from the third pair.
Bloodvessels.-1. branches of the external carotid ramified on the face and the ophthalmic artery from the internal carotid are the sources from which the accessory parts of the eye receive their arteries.
The branches of the external carotid in the face, viz. the facial, the infra-orbital of the in ternal maxillary, the transverse artery of the face and the temporal send ramifications to the eyelids. Towards\the inner canthus the facial ends in the angular artery, which anastomoses with the nasal branch of the ophthalmic. The angular artery, or some one of its branches, is implicated in the operation for fistula lacry malis as it is called.
The ophthalmic artery gives off the lacrymal, usually one of its first branches after its en trance into the orbit. The lacrymal supplies the upper and lower masses of the lacrymal gland, besides other parts in the orbit, and at last issues from that cavity at the external angle of the eye. The muscular arteries of the ophthalmic, after supplying the recti muscles, are continued forward on the front of the eye ball—one from the external rectus muscle, and two from each of the other recti. These arte ries divide into two sets of branches, of which one set ramify in the ocular conjunctiva, and the other set supply the sclerotica.
The ophthalmic, as it issues from the orbit at the internal canthus, gives off the palpebral arteries, superior and inferior. These ramify,
in their respective eyelids, towards the external angle, where they meet and inosculate with the terminating branches of the lacrymal artery. The superior palpebral artery, 'moreover, inos culates with the supra-orbital and anterior tem poral; the inferior palpebral artery with the nasal branch of the ophthalmic, the infra orbital and transverse artery of the face, thus forming the tarsal or palpebral arches: The ramifications sent, from the branches of the external carotid in the face, to the eyelids, and those from the ophthalmic, form by their inosculations a network, from which are sup plied the different structures of the eyelids, the conjunctiva, the lacrymal caruncle, and 'the lacrymal sac.
Where the ocular and palpebral portions of the conjunctiva run into each other, bloodves sels from the muscular enter and subdivide into two sets of branches—one set smaller, to the ocular conjunctiva, the other set larger, to the palpebral conjunctiva. The latter receives another and a still larger set, which enter it at the orbital margin of the tarsal cartilages, anastomose with the first set, and ramify for wards to the free margin of the eyelids.
The bloodvessels of the ocular conjunctiva are few and small in comparison to those of the palpebral. They affect a reticular arrange ment, produced partly by the vessels crossing over each other simply, and partly by inoscu lations. The latter is particularly the case around the cornea. It is only in the inflamed state—in catarrhal ophtlialmia—that the vessels of the ocular conjunctiva can be well seen. In catarrhal ophthalmia, large superficial tor tuous vessels are observed proceeding in a di rection towards the cornea ; a few of the same size are seen crossing these, especially at a dis tance from the cornea. Underneath the large vessels is a network of smaller ones, the branches of the larger. The arrangement of the vessels around the margin of the cornea has been already noticed. It can scarcely be doubted that the large dark-coloured varicose vessels, derived from the muscular, seen in the conjunctiva in the so-called arthritic states of the eye, are veins, as also the largest and most tortuous of those seen in catarrhal ophthalmia.