PAETS FOE THE PEOTECTION OF THE EYEBALL. 139 



Those of the upper lid are longer and more numerous than 

 the lower cilia. The curve of the lashes is from the eyeball. 

 They serve to protect the globe from dust, and, to a certain 

 extent, to shade the eye. 



The tarsal cartilages are small, elongated, semilunar plates, 

 extending from the edges of the lids toward the margin of 

 the orbit. Their length is about an inch. The central por- 

 tion of the upper cartilage is about one-third of an- inch 

 broad, and the corresponding portion of the lower cartilage 

 measures about one-sixth of an inch. At the inner canthus 

 of the eye, is a small, delicate ligament, or tendon, the tendo 

 palpebrarum, which is attached to the lachrymal groove in- 

 ternally, passes outward, and divides into two lamellae, which 

 are attached to the two tarsal cartilages. At the outer can- 

 thus, the cartilages are attached to the malar bone by the ex- 

 ternal tarsal ligament. The tarsal cartilages receive an addi- 

 tional support from the palpebral ligament, a fibrous mem- 

 brane, attached to the margin of the orbit and the convex 

 border of the cartilages, and lying beneath the orbicularis 

 muscle. This membrane is strongest near the outer angle of 

 the eye. 



On the posterior surface of the tarsal cartilages, partly 

 embedded in them and lying just beneath the conjunctiva, 

 are the Meibomian glands. The structure and functions of 

 these glands have already been considered in connection with 

 secretion. 1 They produce an oily fluid, which smears the 

 edges of the eyelids and prevents the overflow of tears. 



Muscles which open and close the Eyelids. Leaving out 

 the corrugator supercilii, which draws the skin of the fore- 

 head downward and inward, we have the orbicularis palpe- 

 brarum, which closes the lids, and the levator palpebrse supe- 

 rioris, which raises the upper lid. The tensor tarsi, called 

 the muscle of Horner, is a very thin, delicate muscle, which 

 is little more than a deep portion of the orbicularis. Con- 

 1 See vol. iii., Secretion, p. 62. 



