400 TARSAL CARTILAGES. TUNICA CONJUNCTIVA. 



generate into cellular tissue, by which they are connected to 

 the fibrous layer of the lids. They present on the inner sur- 

 face a number of vertical grooves in which are lodged the 

 glands of Meibomius. 



Their edges are formed obliquely, and apply to each other 

 in such way, that when the lids are closed a groove is formed 

 between them and the eye ; by which the tears are conveyed 

 towards the nose. 



The use of these cartilages is to keep the eyelids properly 

 expanded ; and to form margins that apply accurately to each 

 other. 



These cartilages are covered internally by the tunica con- 

 junctiva. 



The levator palpebrae muscle, which arises from the bottom 

 of the orbit, at the upper part of the foramen opticum, and 

 passes over the superior muscle of the eyeball, is inserted by 

 a broad thin tendon or aponeurosis into the cartilage of the 

 upper eyelid, and draws it upwards, within the upper margin 

 of the orbit, when the eyelids are opened. 



The antagonist muscle to the levator or that vv'hich closes 

 the lids, is the orbicularis palpebrarum. 



The tunica conjunctiva, that lines the eyelids, is continued 

 from them, without any interruption of the surface, over the 

 anterior part of the ball of the eye ; in the same manner that 

 the reflected membranes are continued from one surface to 

 another. 



Although this membrane is a continuation of the skin, it is 

 essentially different from its structure ; being extremely thin, 

 flexible, and sensible, and also transparent. It abounds with 

 vessels, which do not carry red blood in their natural state, 

 but receive it largely when they are inflamed or much relaxed. 

 It adheres firmly to the cartilage at the edge of the eyelids ; 

 and becomes more loose in its adhesion to the lids, as it 

 proceeds backwards. It is so reflected to the ball of the eye, 

 that it covers and adheres to about one-third of it anteriorly. 

 Where it first joins the eye, the adhesion is loose, but this 

 adhesion becomes firmer as it advances over the eye ; and it 

 cannot be separated from the cornea without maceration, and 



