THE HEAD AND NECK 1187 



Ocular Appendages. 



The appendages of the eye consist of the eyelids and the 

 lachnTnal apparatus. 



Eyelids. — The eyelids, or palpebrae, are two movable curtains, 

 placed in front of the eyeball, to which they form an important 

 protection. The inner surface of each is covered by mucous 

 membrane, which constitutes the conjunctiva. The upper eyelid is 

 larger than the lower, and, when closed, covers the transparent part 

 of the eye or cornea. It is also more movable than the lower, 

 being provided with a special elevator muscle, namely, the levator 

 palpebrae superioris. The elliptical interval between the lids 

 is called the fissura palpebrarum, and the lateral extremities of 

 this fissure are called the outer canthus and inner canthus. The 

 outer canthus is formed by the junction between the two lids. At 

 the inner canthus the lids are separated by a recess, called the 

 lacus lacrimalis, in which there is a small body, called the caruncula 

 lacrimalis. In this region the eyelids are separated from the eyeball 

 by a vertical, semilunar fold of the conjunctiva, called the plica 

 semilunaris. The margin of each eyelid presents, at the com- 

 mencement of the lacus lacrimalis, a slight conical elevation, called 

 the papilla lacrimalis, .the apex of which presents a small orifice, 

 termed the punctum lacrimale, its direction being towards the 

 eyeball. Each punctum is the entrance to a passage, called the 

 canaliculus lacrimalis, by which the tears are conveyed from the 

 surface of the eyeball into the lachrymal sac, and thence, through 

 the nasal duct, into the inferior meatus of the nasal fossa. 



The free margins of the eyelids, external to the puncta lacrimalia, 

 are provided with hairs, called the cilia or eyelashes. They are short, 

 stout, and cun-ed, and are arranged in two rows. Those of the 

 upper lid are more numerous and larger than those of the lower. 

 The upper eyelashes are curved upwards, and the lower downwards, 

 and in this manner intermingling is avoided. Within the lines of 

 attachment of the eyelashes there is a row of modified sweat-glands, 

 known as the glands of Moll, the openings of which are associated 

 with the follicles of the eyelashes, and with the condition known as 

 stye. 



Structure of the Eyelids. — Each eyelid is composed of the following 

 structures, in order from without inwards : 



1. Skin. 4. Tarsal plate. 



2. GDunective tissue. 5. Meibomian glands. 



3. Palpebral fibres of 6. Conjunctiva. 



the orbicularis palpebrarum. 



In addition to the foregoing structures the upper eyelid contains 

 the tendinous insertion of the levator palpebrae superioris muscle. 



The skin is very thin, and at the ciliary margins of the eyelids 

 it becomes continuous with the conjunctiva, which is a mucous 

 membrane. The subcutaneous connective tissue is very loose, and 



