466 THE SENSORIAL FUNCTIONS. 



effect produced by the action of the muscle is a 

 motion in a direction exactly the reverse of that 

 in which its fibres contract. This mechanism, 

 simple as it is, affords one of the most palpable 

 instances that can be adduced of express con- 

 trivance ; for in no other situation could the muscle 

 have been so conveniently lodged as within the 

 eye-ball ; and in no other way could its tendon 

 have been made to pull in a direction contrary to 

 that of the muscle, than by the interposition of a 

 pulley, turning the tendon completely round. 



The fore-part of the globe of the eye, which is 

 of a white colour, is connected with the sur- 

 rounding integuments by a membrane, termed 

 the Conjimctiva* This membrane, on arriving 

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

 as to line their inner surfaces, and to be con- 

 tinuous 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 

 Lacrymal glands. Each gland, (as shown at 

 L, Fig 417,) is situated above the eye, in a hol- 



* An abundant supply of nerves has been bestowed on this 

 membrane for the purpose of conferring upon it that exquisite 

 degree of sensibility which was necessary to give immediate warn- 

 ing of the slightest danger to so important 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. 



