APPENDAGES OF THE EYE. 691 



cular 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 arleria 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 eye- 

 lids, 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 sur- 

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

 short, thick hairs, directed obliquelyon the surface. In structure, the eyebrows 

 consist 01 thickened integument, connected beneath with the Orbicularis Palpe- 

 brarum, Corrugator Supercilii, and Occipito-frontalis muscles. These muscles 

 serve, by their action on this part, to cqntrol 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, and the 

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

 Levator Palpebra3 Superioris. When the eyelids are opened, an elliptical space 

 (fissura palpebrarum) is left between their margins, the angles of which corre- 

 spond 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 lacus cachrymalis. At the commencement of the lacus Jachryrnalis, 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, ihepunctum lachrymale, 

 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 Palpebras. 



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 palpebras, are thin, 

 pale in color, and possess an involuntary action. 



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

 inch in length. They are placed one in each lid, contributing to thei? 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 Palpebrsfl is 

 attached. 



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



The/ree or ciliary margin of the cartilage is thick, and presents a perfectly 

 straight edge. The attached, or orbital margin, is connected to the circumference 



