1044 ORGANS OF SPECIAL SENSE 



(2) Lachrymal, supplying the lachrymal gland, anastomosing with a branch 

 of the maxillary in the orbit, and finally piercing the upper eyelid. Outside the 

 orbit it is distributed to the outer part of the upper lid, the conjunctiva at the ex- 

 ternal canthus, and the skin between this and the temporal region. 



(3) Naso-ciliary, giving off (a) a branch to the ciliary ganglion, constituting its 

 long root; (6) two or three long ciliary turrets; and (c) the infratrochlear, passing out 

 of the orbit. The nerve then leaves the orbit as the anterior ethmoidal nerve, 

 re-entering the cranial cavity before being finally distributed to the nose. The 

 infratrocftlear branch supplies the eyelids and skin of the side of the nose near the 

 inner canthus, the lachrymal sac, caruncle, and plica semilunaris. The anterior 

 ethmoidal nerve, after its course in the cranial cavity, passes through an aperture 

 in the front of the cribriform plate of the ethmoid bone, and is ultimately distributed 

 to the nasal mucous membrane, and to the skin of the side and ridge of the nose near 

 its tip. 



2. The maxillary division of the fifth nerve gives a branch, called the zygo- 

 matic nerve, which passes into the orbit through the inferior orbital fissure, anas- 

 tomoses with the lachrymal, and leaves the orbit in two divisions. These are dis- 

 tributed to the skin of the temple and of the prominent part of the cheek. 



A few minute twigs from the spheno-palatine ganglion, and sometimes from the 

 maxillary division of the fifth nerve, also pass through the inferior orbital fissure to 

 supply the periorbita in this neighbourhood. 



C. The sympathetic nerves of the orbit are mainly derived from the plexus on 

 the internal carotid. With the exception of branches accompanying the ophthalmic 

 artery, and of the distinct sympathetic root of the ciliary ganglion, they enter the 

 orbit in the substance of the other nerve-cords. The connections between the ocular 

 nerves and the carotid plexus are recognisable as fibres going to the third, sixth, and 

 ophthalmic nerves; as a rule, the comparatively large twigs going to the sixth join 

 it furthest back, and those to the third furthest forwards. Sympathetic connections 

 with the fourth nerve are very doubtful. The special courses of the motor fibres to 

 the dilator pupillae have already been described. 



The ciliary ganglion is situated between the optic nerve and external rectus 

 far back in the orbit. Its three roots motor, sensory, and sympathetic have been 

 already mentioned. Anteriorly, it gives off three to six small trunks, which sub- 

 divide to form the short ciliary nerves, about twenty in number, piercing the 

 sclerotic around the optic nerve entrance. 



The lymphatic system of the orbit. Although there are no lymphatic res- 

 sds or glands in the orbit, the passage of lymph is nevertheless well provided for. 

 We have already observed the lymph channels within, between, and outside the 

 sheaths of the optic nerve, and have seen how these communicate anteriorly with 

 the lymph channels of the eyeball, and posteriorly with the intracranial meningeal 

 spaces. In addition, there are lymph-spaces around the blood-vessels, situated 

 between the outer coat and the loose investment furnished by the muscle fascia. 

 The nerves of the orbit (apart from, the optic) are probably similarly surrounded 

 by lymph-spaces. In the absence of lymphatic vessels it is difficult to trace the 

 circulation thoroughly; much of the lymph from the orbital cavity is said to pass 

 into the parotid nodes. 



THE EYELIDS 



The cutaneous and conjunctival surfaces of the lids have already been examined, 

 and the position of the tarsus has been indicated. We have now to ascertain the 

 nature and relations of the tarsus, and describe the other tissues entering into the 

 formation of the eyelids. 



The skin here is thin, bearing fine hairs, and having small sebaceous and numerous 

 small sweat-glands. Immediately beneath it is a loose subcutaneous tissue, des- 

 titute of fat, separating the skin from the palpebral part of the orbicularis muscle. 

 The lid-fibres of this muscle arise from the inner palpebral ligament, and course 

 over the whole upper and lower eyelids in a succession of arches, so as to meet 

 again beyond the outer canthus; there they in part join one another, in part are 

 inserted into the outer palpebral raphe. The muscular fibres are arranged in loose 

 bundles, with spaces between them occupied by connective tissue: in the 

 upper lid these connective-tissue fibres may be traced upwards and backwards into 

 the fibrous expansion of the tendon of the levator palpebne superioris. One strong 



