THE APPENDAGES OF THE EYE. 907 



iiiir it harder than in youth, so that its curvature can only be altered to a limited extent by the 

 Ciliary muscle. And, finally, the lens may be dislocated or displaced by blows upon the eyeball, 

 and its relations to surrounding structures altered by adhesions or the pressure of new growths. 

 There are two particular regions of the eye which require special notice : one of these is 

 known as the " filtration area," and the other as the " dangerous area." The filtration area is 

 the circumcoraeal zone immediately in front of the iris. Here are situated the cavernous spaces 

 of Fontana. which communicate with the canal of Schlemm, through which the chief transuda- 

 tion of fluid from the eye is now believed to take place. The dangerous area of the eye is the 

 region in the neighborhood of the ciliary body, and wounds or injuries in this situation are 

 peculiarly dangerous ; for inflammation of the ciliary body is liable to spread to many of the 

 other structures of the eye, especially to the iris and chorpid, which are intimately connected by 

 nervous and vascular supplies. Moreover, wounds which involve the ciliary region are especially 

 liable to be followed by sympathetic ophthalmia, in which destructive inflammation of one eye 

 is excited by some irritation in the other. 



The Appendages of the Eye. 



The appendages of the eye (tutamina oculi) include the eyebrows, the eyelids, 

 the conjunctiva, and the lachrymal apparatus viz. the lachrymal gland, the 

 lachrymal sac, and the nasal duct. 



The eyebrows (supercilid) are two arched eminences of integument which 

 surmount the upper circumference of the orbit on each side, and support numer- 

 ous short, thick hairs, directed obliquely on the surface. In structure the eye- 

 brows consist of thickened integument, connected beneath with the Orbicularis 

 palpebrarum, Corrugator supercilii, and Occipito-frontalis muscles. These mus- 

 cles serve, by their action on this part, to control to a certain extent the amount 

 of light admitted into the eye. 



The eyelids (palpebrce) are two thin, movable folds placed in front of the 

 eve. protecting it from injury by their closure. The upper lid is the larger 

 and the more movable of the two, and is furnished with a separate elevator 

 muscle, the Levator palpebrce superioris. When the eyelids are opened an 

 elliptical space (fissura palpebraruni) is left between their margins, the angles 

 of which correspond to the junction of the upper and lower lids, and are 

 called eanthi. 



The outer canthus is more acute than the inner, and the lids here lie in close 

 contact with the globe ; but the inner canthus is prolonged for a short distance 

 inward toward the nose, and the two lids are separated by a triangular space, the 

 lurus lachrymalis. At the commencement of the lacus lachrymalis, on the margin 

 of each eyelid, is a small conical elevation, the lachrymal papilla, or tubercle, the 

 apex of which is pierced by a small orifice, the punctum lachrymale, the com- 

 mencement of the lachrymal canal. 



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 

 upward ; those of the lower lid curve downward, so that they do not interlace in 

 closing the lids. Near the attachment of the eyelashes are the openings of a 

 number of glands, glands of Mohl, arranged in several rows close to the free 

 margin of the lid. They resemble in structure a portion of a sweat-gland, and 

 are regarded as the modified sweat-glands of this region. 



Structure of the Eyelids. The eyelids are composed of the following struc- 

 tures, taken in their order from without inward : 



Integument, areolar tissue, fibres of the Orbicularis muscle, tarsal plate 

 (cartilage), and its ligament, Meibomian glands and conjunctiva. The upper lid 

 has, in addition, the aponeurosis of the Levator palpebrse. 



The integument is extremely thin, and continuous at the margin of the lids 

 with the conjunctiva. 



The subcutaneous areolar tissue is very lax and delicate, seldom contains any 

 fat, and is extremely liable to serous infiltration. 



The fibres of the Orbicularis muscle, where they cover the palpebrae, are thin, 

 pale in color, and possess an involuntary action. 



