APPENDAGES OF THE EYE. . 625 



The anterior ciliary arteries, five or six in number, are branches of the muscular 

 and lachrymal branches of the ophthalmic. They pierce the eyeball, at the 

 anterior part of the sclerotic, immediately behind the margin of the cornea, and 

 are distributed to the ciliary processes, some branches joining the greater vascular 

 circle of the iris. 



The arteria centralis retinse has been already described. 



The veins, usually four in number, are formed mainly by branches from the 

 surface of the choroid. They perforate the sclerotic, midway between the cornea 

 and the optic nerve, and end in the ophthalmic vein. 



The nerves of the eyeball are the optic, the long ciliary nerves from the nasal 

 branch of the ophthalmic, and the short ciliary nerves from the ciliary ganglion. 



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 (supercilia) are two arched eminences of integument, which 

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

 short, thick hairs, directed obliquely on the surface. In structure, they consist 

 of thickened integument, connected beneath with the Orbicularis palpebrarum, 

 Corrugator supercilii, and Occipito-frontalis muscles. These muscles serve, by 

 their action on this part, to control to a certain extent the amount of light admitted 

 into the eye. 



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

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

 movable of the two, and supplied by a separate elevator muscle, the Levator 

 palpebrse superioris. "When the eyelids are opened, an elliptical space (fissura 

 palpebrarum} is left between their margins, the angles of which correspond to the 

 junction of the upper and lower lids, and are called canthi. 



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 

 inwards, towards the nose, and the two lids are separated by a triangular space, 

 the locus lacrymalis. At the commencement of the lacus lacrymalis, 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 vunctum lacrymale, 

 the commencement of the lachrymal canal. 



Structure of the eyelids. The eyelids are composed of the following structures, 

 taken in their order from without inwards : 



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

 fibrous membrane, Meibomian glands, and conjunctiva. The upper lid has, in 

 addition, the aponeurosis of the Levator palpebraB. 



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. 



The tarsal cartilages are two thin elongated plates of nbro-cartilage, about an 

 inch in length. They are placed one in each lid, contributing to their form and 

 support. 



The superior, the larger, is of a semilunar form, about one-third of an inch 

 in breadth at the centre, and becoming gradually narrowed at each extremity. 

 Into the fore part of this cartilage the aponeurosis of the Levator palpebrse is 

 attached. 



The inferior tarsal cartilage, the smaller, is thinner, and of an elliptical 

 form. 



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