259 



OF THE SENSES, ORGANA SENSORIA. 



490. 1. The organ of Sight, the Eye, Organon visus, oculus. 



The eye is placed in the orbit (see Osteology), and is moved, for 

 the complete performance of its functions, by six proper muscles, 

 (see Myology), protected by certain contrivances, and by others 

 maintained in a lubricated state. 



A. Accessory Organs, Tutamina oculi. 



491. 1. The eyebrows, supercilia, 



two arched enlargements of the skin along the superior border of the 

 basis of the orbits, are beset with short, stiff hairs, directed towards 

 the temples, which are arranged more closely, inwards towards the 

 nose, and are, rarely only, continued over the root of the nose 

 (by intercilia). The skin is thick, lies firmly upon a muscular 

 layer ofm.frontalis, orbicular, and superciliaris ; is provided with 

 numerous nerves from n.facialis and trigeminus, and with vessels 

 from ophthalmicm and temporalis. Uses : The eyebrows protect 

 the eyes against too strong light, and from the perspiration flowing 

 down from the forehead ; they serve, besides, for the expression of 

 the face. 



492. 2. The eyelids, palpebrce, 



two movable cutaneous curtains, which, passing off from the su- 

 perior and inferior border of the base of the orbits completely shut 

 up the eye when they are approximated. They consist of skin, 

 muscular fibres, cartilage and mucous membrane. The anterior 

 or cutaneous surface is convex, and folded across ; the posterior 

 surface turned towards the globe of the eye, concave and beset 

 with yellowish, vertical lines (glandul. Meibom.). The free bor- 

 ders are in the open eye curvilinear, and they bound an elliptical 

 space, in the closed eye rectilinear, and only leave a narrow fis- 

 sure, rima palpebrar., but not a triangular canal between them. 

 The anterior edge of the free borders is beset with, three rows of 

 short, stiff and curved hairs, cilia, eyelashes, the points of which 

 diverge from one another ; the posterior edge presents a regular row 

 of (twenty-five to thirty) small openings (see Meibomian Glands, 

 493.) At the last [internal] one-sixth of the free border, it presents 

 a tubercle provided with an opening, the lacrymcd punctum. From 

 this point inwards there are neither cilia nor openings any longer 



