ORGANS OF SPECIAL SENSE. 357 



On the nasal side the lids are separated by a triangular 

 space the lacus lachrymalis at the outer angles of which are 

 the lachrymal papillce, surmounted by the puncta lachrymalia, 

 the commencements of the lachrymal canal. The lacus lachry- 

 malis is filled by the coruncula lachrymalis, a mass of follicles 

 rvsembling the Meibomian glands, and covered by the con-* 

 junctiva. 



The structure of the eyelids, from without inward, is as 

 follows : 



Skin, subcutaneous areolar tissue, fibres of the orbicularis muscle, 

 tarsal cartilage, fibrous membrane, Meibomean glands, vessels, and 

 nerves; 



The slfin is thin, and attached by a very loose areolar tissue to the 

 muscle beneath; 



The fibres of the orbicularis are pale, thin, and act involuntarily; 



The tarsal cartilages are two plates of firm connective tissue; the 

 superior, the larger, is semilunar in shape, the inferior is elliptical. The 

 inner margins are fixed to the orbit by tendo oculi; 



The fibrous membrane of the lids, or tarsal ligament, passes over 

 the anterior surface of the tarsal cartilage, being attached to its free 

 margin below and to the margin of the orbit externally; 



The Meibomian glands, about thirty in number in the upper, a few 

 less in the lower lid, are arranged vertically on the inner surface of the 

 cartilages; they are straight, sebaceous follicles, into which open a 

 number -of secondary follicles, terminating above in a blunt extremity, 

 and opening below on the free margin of the lids by small foramina, cor- 

 responding to the number of tubules; 



The eyelashes, or cilia, are arranged on the free border of the lids 

 in two or three rows. 



THE CONJUNCTIVA is the mucous lining membrane of the 

 front of the eye. It consists of two portions the ocular, re- 

 flected over the sclerotic and cornea, and the palpebral portion, 

 lining the internal surface of the lids. 



The ocular portion is loosely connected with the sclerotic, 

 but over the cornea it becomes very thin, consisting only of the 

 epithelial layer. 



The palpebral portion is thick, highly vascular, and contains 

 many papillae. At the inner angle of the eye it forms a semi- 

 lunar fold, the plica semilunaris the rudiment of the nictitating 

 membrane of birds, the wcnihmna nictitans. 



The point of reflection is called the fornix conjunctive, 

 and the reflected portions the superior and inferior palpclnil 

 folds. 



The lachrymal apparatus consists of the lachrymal gland, 

 canals, sac, and nasal duct. 



THK i. AC i IKY MAI, CLAND is an oval, glandular body, about 

 the shape and si/e of an almond, situated in a depression in the 

 upper surface of the orbit near (lie external angular process. 



