SPECIAL ANATOMY. 



121 



root of the orbital process of the frontal bone to the npper 

 eyelid, where it blends with orbicularis, from the lower 

 part of which muscle levator labii superioris alseque nasi 

 and zjgomaticus in part take their origin. The eyelids, 

 therefore, are two semilunar folds which are adapted to 

 cover the anterior surface of the eyeball. They are com- 

 posed externally of skin, internally of mucous membrane, 

 nam-ed the conjunctiva, which becomes reflected over the 

 tunica albuginea and the cornea, thus covering all that 

 portion of the eye which is naturally visible, and serving 

 to retain the eyeball in its proper relation with the palpe- 

 bral fissure, by its smooth surface to facilitate the move- 

 ments of the eyelids, and to protect the eye. That portion 

 of it which lines the eyelids and covers the tunica albu- 

 ginea is vascular, but its continuation ovei' the cornea is 

 simjjly a basement membrane, with a single layer of tesse- 

 lated epithelial cells, which is transparent and thus causes 

 no obstruction to vision. Between these two layers of the 

 eyelid are situated muscular structure, vessels, nerves, the 

 meibomian glands and the tarsal ligament. ^ The free 

 borders of the eyelids are broad and only come into appo- 

 sition by their outer edges when the lids meet ; thus a trian- 

 gular canal is formed by which the tears are directed 

 towards the inner angle of the palpehral fissure, the space 

 between the eyelids. Along the outer edge of this margin 

 we see the eyelashes, cilise ; long curved hairs, those of 

 the upper lid, the strongest and longest, run in an upward 

 direction, those of the lower lid downwards. This margin 

 also presents in each eyelid a row of openings of the 

 meibomian glands, and at the inner extremity a much larger 

 opening ; these latter are the puncta lachrymalia, through 

 which the tears pass on their way from the front of the 

 eye to the nasal chamber. The points at which the eye- 

 lids meet are termed the cantM ; the outer or temporal 

 cantlius is in the form of an acute angle, and here the 

 eyelids are in direct contact with the eyeball ; the inner 

 or nasal canthus presents a rounded diverticulum in which 

 is situated a small rounded nodular body covered by a 

 very thin dark skin which presents a few short and fine 

 hairs. This is the canincula lachrymalis, which is merely 

 a mass of connective tissue and vessels, and is situated 

 between the puncta lachrymalia into which it serves to 

 direct the tears. Before departing from consideration of 



