832 tht: apparatus of the senses. 



4. Elevator Muscle of the Upper Eyelid, or Oebito-palpebkalis 

 (Levator palpebrm). — When the ocular sphincter ceases to contract, the 

 lower eyelid droops from its own weight ; the upper lid, however, requires 

 some special muscular agency to raise it, and this it finds in the levator. 

 This is a very thin, narrow, fleshy-band, lodged in the ocular sheath with 

 the other muscles of the eyeball, and is related to the superior rectus, whose 

 course it follows. On reaching the lachrymal gland, it expands into a wide 

 aponeurotic membrane that passes between the conjunctiva and the fibrous 

 plate of the eyelid, and terminates on the tarsus. 



It will be seen that this muscle is inflected on the eyeball in a pulley- 

 like manner, and it is owing to this disposition that it has the power of 

 raising the lid. If the eyeball were not present, the muscle would draw the 

 free margin of the lid towards the back of the orbit, instead of elevating it. 



5. Integuments op the Eyelids. — The different layers enumerated are 

 comprised between two tegumentary folds, the sJcin and conjunctiva, which 

 are continuous at the border of the eyelids. We will examine these, with 

 their appendages — the eyelashes and Meibomian glands. 



a. Skin. — -Intimately adhering, by its inner face, to the orbicularis 

 muscle, this membrane is thin (smooth), and covered with numerous fine 

 short hairs. In the fcetus, it shows at the orbital arch, when the skin 

 everywhere else is nude, a well-marked semicircle of hairs — the eyebrow. 

 Fat is never found beneath it. 



b. Conjunctiva. — The conjunctiva, as its name indicates, joins the eyelids 

 to the eyeball. Very fine and highly vascular, this mucous membrane is 

 a continuation of the skin at the border of the lids, lines the inner face of 

 each of them, envelops the anterior portion of the membrana nictitans in a 

 particular fold, covers the caruncula lachrymalis, and enters the puncta ; 

 it is then reflected, at the adherent border of the eyelids, on to the eyeball, 

 extending over the sclerotic and terminal aponeurotic expansion of the recti 

 muscles. On arriving at the margin of the cornea, it is impossible to trace 

 it further; though it is represented by the thin layer of pavement epithelium 

 already described. At the surface of the lachrymal caruncle, it shows 

 some very fine hair bulbs. It possesses some papillse (on the palpebral 

 portion only, the ocular reflection being thinner, and having none of these 

 nervous processes), and tubular and aggregate glands, as well as closed 

 follicles. We have found large numbers of the latter, whose volume was 

 considerable ; they form a corona around the cornea. 



The nerves of the conjunctiva terminate by small oval enlargements, 

 the corpuscles of Krause. 



(The ocular portion has generally very few blood-vessels visible in health ; 

 when inflamed it becomes intensely red and vascular.) 



c. Eyelashes. — These are two rows of hairs {cilia) implanted in the free 

 border of the lids, and destined to prevent the entrance of dust and small 

 particles of foreign matter into the eye. They are much longer, and more 

 abundant and stronger, in the upper than the lower lid, their presence there 

 being more necessary, as extraneous particles are most likely to enter the eye 

 when falling. But if the eyelashes of the lower lid are few and rudimentary, 

 this is compensated for by the presence on its surface of some long bristly 

 hairs, scattered here and there, and exactly like the tentacula of the lips. 



Like all hairs, without exception, the eyelashes are flanked at their 

 base by two or three small sebaceous glands, whose duct opens into their 

 foUicle. 



d. Meibomian glands. — These are little masses, analogous to sebaceous 



