864 ORGANS OF SPECIAL SENSE 



posterior third of these muscles is, however, comparatively ill supplied with lioth 

 kinds of plexus and with nerve-endings. 



B. The sensory nerves are supplied by the tirst and second divisions of the 

 fifth cranial nerve. The tirst division, or ophthalmic nerve, is entirely orbital; 

 while the second, or maxillary, only sends a small branch to the orbit. 



1. The ophthalmic division of the fifth nerve enters the orbit in three 

 divisions, namely: — 



(1) Frontal, splitting subsequently into supratrochlear and sujwaorbital, both 

 passing out of the orbit. It is distributed to the corresponding ui)i)er eyelid, and 

 the skin over the root of the nose, the forehead, and the hairy scalp as far back as 

 the coronal suture on the same side. It also gives branches to the periosteum in 

 this region, and to the frontal sinus. 



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

 of the superior maxillary in the orbit, aiid finally piercing the upper eyelid. Out- 

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

 the external eanthus, and the skin between this and the temporal region. 



(3) Nasal, giving off (a) a branch to the ciliary ganglion, constituting its long 

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

 the orbit. The nasal nerve then leaves the orbit, re-entering the cranial cavity 

 before being finally distributed to the nose. The infratrochlear branch supplies the 

 eyelids and skin of the side of the nose near the inner eanthus, the lachrymal sac, 

 caruncle, and plica semilunaris. The nasal nerve, after its second 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 orbital 

 nerve, which passes into the orbit through the spheno-maxillary fissure, anasto- 

 moses with the lachrymal, and leaves the orbit in two divisions. These are 

 distril)Uted to the skin of the temple and of the prominent part of the cheek. 



A few minute twigs from Meckel's ganglion^ and sometimes from the maxillary 

 division of the fifth nerve, also pass through the spheno-maxillary fissure to supply 

 the periorbita in this neighbourhood. 



C. The sympathetic nerves of the orbit are 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, the}' enter the 

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

 nerves and the carotid plexus are recognisal:)le 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 forward. Sym])athetic connections 

 with the fourth nerve are very doubtful. 



The lenticular or ciliary ganglion is situated between the optic nerve and 

 external rectus far back in the orbit. Its three roots — motor, sensor}', and sympa- 

 thetic — have been already mentioned. Anteriorly, it gives off three to six small 

 trunks, which subdivide to form the short ciliary nerves, about twenty in num- 

 ber, ])iercing the sclerotic around the o])tic nerve entrance. 



The lymphatic system of the orbit. — Although there are no lym])hatic 

 vessels or (jlanxh in the orbit, the passage of lymph is nevertheless well ])rovided 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 lymi)hatic vessels it is difficult to trace the 

 circulation thoroughly; much of the lymph from the orbital cavity is .^Jaid to pass 

 into the internal maxillarv glands. 



