1076 



SPECIAL SENSE ORGANS 



in the orbit, and finally piercing the upper eyelid. Outside the orbit it is distributed to the 

 lateral part of the upper lid, the conjunctiva at the lateral angle, and the skin between this and 

 the temporal region. 



(3) Naso-ciliary [n. naso-ciliaris] giving off — (c) a branch to the ciliary ganghon, constituting 

 its long root; (b) two or three long ciliary nerves; and (c) the infratrochlear, passing out of the orbit. 

 The nerve then leaves the orbit as the anterior ethmoidal nerve [n. ethmoidalis anterior], re- 

 entering the cranial cavity before being finally distributed to the nose. The infratrochlear branch 

 [n. infratrochlearis], supplies theeyehds and skin of the side of the nose near the medial angle of 

 the eye, the lacrimal sac, caruncle, and pUca semilunaris. The anterior ethmoidal nerve, after 

 its course in the cranial cavity, passes through an aperture in the front of the lamina cribrosa 

 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 zygomatic nerve, 

 which passes into the orbit through the inferior orbital fissure, anastomoses with the lacrimal, 

 and leaves the orbit in two divisions. These are distributed to the skin of the temple and of the 

 prominent part of the cheek. 



A few minute twigs from the spheno-palatine ganghon, 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 artery. 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 



Fig. 820. — Section through Contents of Right Orbit, 1-2 mm. in front of the Optic 

 Foramen, viewed from behind. (After Lange.) 



Trochlear nerve 

 Superior rectus and levator palpe- 



brse superioris muscles ^ 



Superior oblique muscle 

 Optic nerve- 

 Medial rectus muscle- 

 Inferior rectus muscle 



Ophthalmic vein 

 phthalmic i 

 naso-ciliar 

 branches) 



_^ ^ "% Ophthalmic nerve (frontal, 

 1 (^ ^ ^ ~V ^ naso-ciliary, and lacrimal 



::^^ ' ■ ■ 



U , 



Ophthalmic vein 





^in~7 



Ophthalmic artery 



Abducens nerve 



Oculomotor nerve 

 Lateral rectus muscle 



the other nerve-cords. The connections between the ocular nerves and the carotid plexus are 

 recognisable as fibres going to the oculomotor, abducens, and ophthalmic nerves; as a rule, the 

 comparatively large twigs going to the abducens join it furthest back, and those to the oculo- 

 motor furthest forward. Sympathetic connections with the trochlear nerve are very doubt- 

 ful. The special courses of the motor fibres to the dilatator pupiUse muscle have already been 

 described. 



The ciliary ganglion is situated between the optic nerve and lateral rectus far back in the 

 orbit. Its tliree roots — motor^ sensory, and sympathetic— have been already mentioned. 

 Anteriorly, it gives off three to six small trunks, which subdivide to form the short ciliary nerves 

 [nn. cihares breves] about twenty in number, piercing the sclera around the optic nerve 

 entrance. 



The lymphatic system of the orbit. — Although there are no lymphatic vessels 

 or glands in the or\nt, 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 orl^it (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 eyelids [palpebrae] have al- 

 ready been examined (p. 1053), 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 (fig. 821). 



