692 



ORGANS OF SENSE. 



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 liga- 

 ment. The inner angles of the two cartilages terminate at the commencement 

 of the lacus lachrymalis, 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 mem- 

 brane, 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. 374) are situated upon the inner surface of the 

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



Fig. 374. The Meibomian Glands, etc., seen from the Inner Surface of the Eyelids. 



seen through the mucous membrane on everting the eyelids, presenting the ap- 

 pearance of parallel strings of pearls. They are about thirty in number in the 

 upper cartilage, 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 csecal 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, 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 down.wards, so that they do not 

 interlace in closing the lids. 



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

 face of the eyelids, and is reflected over the forepart of the sclerotic and cornea. 

 In each of these situations, its structure presents some peculiarities. 



The palpebral portion of the conjunctiva is thick, opaque, highly vascular, and 



