THE EYELIDS. 399 



expression of the eye depends upon the depression of the inter- 

 nal angle below the level of the outer. 



The cellular tissue of the eyelids is very lax, but comprises 

 no adipose membrane. Hence the lids may suffer from cedema- 

 tous or sanguineous effusions, but are never burthened with fat. 

 The two lids unite at the extremities of the transverse fissure, 

 and form two angles, or canthi, the internal of which is the 

 largest, and is called the great canthus. This is owing to the 

 insertion of the orbicularis at the internal canthus upon a round 

 tendon, which does not exist at the outer canthus. 



The upper eyelids, therefore, are composed of the skin, of 

 some fibres of the orbicularis muscle, of the tendon of the leva- 

 tor palpebrae superioris muscle, of the cartilaginous plate, and 

 of the tunica conjunctiva. The under eyelid is formed in the 

 same way, with the exception of the cartilage, which, in it, is 

 confined to the margin. There is besides no muscle or tendon 

 in this lid analogous to the levator palpebrae superioris. 



These cartilages form the margin of each eyelid, which is 

 called Tarsus. The upper cartilage is broad in the middle, 

 and narrow at each extremity, and accommodated to the form 

 of the eyeball and eyelid. The under cartilage is a narrow 

 flat rim, which does not extend far from the margin of the eye- 

 lid. A thin delicate membrane is extended from the upper 

 and lower margins of the orbit to these cartilages, and has been 

 considered as forming ligaments for them. 



These cartilages are closely connected together by some 

 fibrous matter* at the external canthus, but terminate short of 

 each other at the internal, by an attachment to the bifid extre- 

 mity of the round tendon, in order to allow space for the 

 lachrymal puncta and ducts. The superior tarsal cartilage, is 

 much broadest in the middle, where it is about six lines wide. 

 The inferior is about two lines in breadth, and is nearly of the 

 same width in its whole extent. Their adhering borders, de- 



* This fibrous matter, is part of a thin ligamentous expansion continuous 

 with the periosteum of the socket, attached to the margin of the tarsal cartilages, 

 and placed between the conjunctiva and orbicularis muscle. It is sometimes 

 called hg amentum latum palpebrarum. P. 



