330 THE SENSORIAL FUNCTIONS. 



arriving at the base of the eye-lids, is folded forwards so as 

 to line their inner surfaces, and to be continuous with the 

 skin which covers their outer sides. The surfaces of the 

 conjunctiva and of the cornea are kept constantly moist by 

 the tears, which are as constantly secreted by the Lacry- 

 mal glands. Each gland, (as shown at L, Fig. 417,) is si- 



tuated above the eye, in a hollow of the orbit, and the ducts 

 (D) proceeding from it open upon the inner side of the up- 

 per eye-lid (E.) This fluid, the uses of which are obviously 

 to wash away dust, or other irritating substances which may 

 happen to get introduced, is distributed over the outer sur- 

 face of the eye by means of the eye-lids. Each lid is sup- 

 ported by an elastic plate of cartilage, shaped like a cres- 

 cent, and covered by integuments. An orbicular muscle, 

 the fibres of which run in a circular direction, immediately 

 underneath the skin, all round the eye,* is provided for 

 closing them. The upper eye-lid is raised by a separate 

 muscle, contained within the orbit, immediately above the 



was necessary to give immediate warning- of the slightest danger to so im- 

 portant an organ as the eye from the intrusion of foreign bodies. That this 

 is the intention is apparent from the fact that the internal parts of the eye 

 possess but little sensibility compared with the external surface. 

 * See Fig. 46, vol. i. p. 105. 



