356 TARSAL CARTILAGES TUNICA CONJUNCTIVA. 



be extremely inconvenient. The muscle, called orbicularis 

 palpebrarum, has been already described as a broad, ellip- 

 tical sheet of pale semi-circular fibres, covering each tar- 

 sus and connected at each canthus, by whose action the 

 lids are closed. 



The tarsal cartilages are thin, elastic plates of fibro car- 

 tilage, which support and preserve the form of the eyelids. 

 The one belonging to the upper lid is semi-lunar, broad in 

 the middle and tapering at either extremity. It lies be- 

 tween the orbiculari and levator palpebrse muscles. Its 

 lower border or free margin is thick. Its upper or orbital 

 edge is thin, for the attachment of the levator palpebree 

 and broad ligament of the tarsus, which fixes the cartilage 

 to the base of the orbit. This fibrous ligament is continu- 

 ous with the periosteum at the base of the orbit. It is 

 thicker at the outer than at the inner portion of the lid. It 

 attaches the extremity of this lid to the outer canthus, and, 

 extends to the lower lid, which it supports and connects in 

 a similar manner ; at the inner canthus the tendo oculi 

 serves to fix the tarsi at this point. The tarsal cartilage of 

 the lower lid is much narrower than that of the superior. 

 The free margins of both lids are furnished with strong, 

 stiff, and curved hairs, arranged in triple, sometimes quad- 

 ruple rows, and called cilice. Those of the upper lid are 

 longer and stronger than the lower, and curve upward. 

 Those in the lower curve downward, so that when the lids 

 are closed, they cannot interfere with each other, as they 

 only touch at their convexities. The eye-lashes, thus ar- 

 ranged, serve to shade the eye from the intensity of light, 

 and to guard it from particles of dust and foreign bodies. 



The tunica conjunctiva forms the mucous membrane of 

 the lids and eye. It is situated on the posterior surface of 

 the tarsal cartilages which it lines, and is then reflected 

 upon the ball of the eye, forming at the angle of this re- 

 flection in the upper lid, the superior, palpebral sinus, and 

 in the lower the inferior palpebral sinus. On the eye it 

 covers about the anterior third, being connected by cellular 

 tissue, which is loose till it reaches the cornea. It is traced 



