626 ORGANS OP THE SENSES. 



The free or ciliary margin of the cartilages is thick, and presents a perfectly 

 straight edge. The attached or orbital margin is connected to the circumference 

 of the orbit by the fibrous membrane of the lids. The outer angle of each 

 cartilage is attached to the malar bone by the external palpebral or tarsal ligament. 

 The inner angles of 'the two cartilages terminate at the commencement of the lacus 

 lacrymalis, being fixed to the margins of the orbit by the tendo oculi. 



The fibrous membrane of the lids, or tarsal ligament is a layer of fibrous 

 membrane, beneath the Orbicularis, attached, externally, to the margin of the 

 orbit, and internally to the orbital margin of the lids. It is thick and dense at 

 the outer part of the orbit, but becomes thinner as it approaches the cartilages. 

 This membrane serves to support the eyelids, and retains the tarsal cartilages in 

 their position. 



The Meibomian glands (fig. 309) are situated upon the inner surface of the 

 eyelids, between the tarsal cartilages and conjunctiva, and" may be distinctly seen 

 through the mucous membrane on everting the eyelids, presenting the appearance 

 of parallel strings of pearls. They are about thirty in number in the upper cartikge, 



Fig. 309. The Meibomian Glands, etc., seen from the Inner Surface 

 of the Eyelids. 



and somewhat fewer in the lower. They are imbedded in grooves in the inner 

 surface of the cartilages, and correspond in length with the breadth of each 

 cartilage ; they are, consequently, longer in the upper than in the lower eyelid. 

 Their ducts open on the free margin of the lids by minute foramina, which 

 correspond in number to the follicles. These glands are a variety of the 

 cutaneous sebaceous glands, each consisting of a single straight tube or follicle, 

 having a coecal termination, into which open a number of small secondary follicles. 

 The tubes consist of basement membrane, covered by a layer of scaly epithelium ; 

 the cells are charged with sebaceous matter, which constitutes the secretion. The 

 peculiar parallel arrangement of these glands side by side forms a smooth layer, 

 admirably adapted to .the surface of the globe, over which they constantly glide. 

 The use of their secretion is to prevent adhesion of the lids. 



The eyelashes (cilia) are attached to the free edges of the eyelids ; they are 

 short, thick, curved hairs, arranged in a double or triple row at the margin of the 

 lids; those of the upper lid, more numerous and longer than the lower, curve 

 upwards; those of the lower lid curve downwards, by which means they do not 

 interlace in closing the lids. 



The conjunctiva is the mucous membrane of the eye. It lines the inner surface 



