APPENDAGES OF THE EYE. 539 



Entering into the structure of the eyelids, there are, therefore, 

 skin, muscles, fibrous tissue, tarsal cartilage, Meibomian glands, 

 and conjunctiva. The skin covering the eyelids is very tine, and 

 adheres intimately to the levator palpebrse and orbicularis palpe- 

 brarum muscles. The fibrous tissue, thickest in the inferior eye- 

 lid, is firmly attached by its adherent border to the periosteum 

 of the orbit, and the bone under the eyebrow, and by its free 

 border to the tarsal cartilage, hence it is sometimes termed the 

 tarsal ligament. The tarsal cartilages are the two cartilaginous 

 plates which form the solid framework of the free border of the 

 eyelids. They are elongated, narrowest at their extremities, and 

 thin on their attached borders, which are continuous with the 

 fibrous membrane. These cartilages afford a firm and very pliant 

 support to the eyelids, and present on the side next the globe of 

 the eye a series of vertical furrows, which lodge the ciliary 

 follicles. The tarsal cartilage of the superior lid is longer and 

 thicker than that of the interior. 



The CILIARY FOLLICLES, or MEIBOMIAN GLANDS, are situated 

 between the tarsal cartilages and the conjunctiva. Each gland 

 consists of a single tube, into which a cluster of follicles opens, 

 and the whole row of glands along the edge of the cartilage bears 

 a strong resemblance to a string of beads. These glands secrete 

 a sebaceous fluid, which prevents the eyelids adhering together 

 during sleep. 



The CONJUNCTIVA, the mucous membrane of the eye, is very 

 thin and very vascular, its vascularity being greatest on the inner 

 surface of the lids, and least on the cornea, where in health no 

 vessels are traceable. It lines the entire inner surface of the eye- 

 lids, being continuous with the skin on their edges, covers the 

 anterior part of the membrana nictitans, and passes down the 

 nasal duct. It is reflected over the whole of the anterior portion 

 of the globe ; adhering very loosely to the sclerotic and aponeu- 

 rotic expansion of the recti muscles, and very firmly to the cornea, 

 where it is extremely delicate and transparent. 



The MEMBRANA NICTITANS, or accessory eyelid, vulgarly the 

 "haw of the eye," is situated near the nasal angle, between the 

 globe and the side of the orbit. It is composed of elastic fibro- 

 cartilage, and is irregular in form, being thick and somewhat 

 prismatic at its base, and thin anteriorly, where it is covered by 

 a fold of conjunctiva. Posteriorly, it is continuous with the pad 

 of fat which is insinuated between all the muscles of the eye. 



