THE EYE. 397 



CHAPTER XIV. 



OF THE' EYE. 



It will be very proper to read the description of the orbit of the eye at page 120, 

 volume 1st, as an introduction to the following description of the organ. 



In addition to that account of the bones, it is to be observed that processes of 

 the dura mater pass through the foramina optica and lacera, which line the 

 cavity of the orbit, and unite with the periosteum at the margin of it. 



THE eye is an optical instrument of a spherical form, which 

 lies in the orbit, in a bed of cellular membrane, more or less 

 filled with adeps for the convenience of its motions. Con- 

 nected with -the ball of the eye, are several auxiliary parts 

 which are calculated for its motion and protection, as well as 

 accommodation in other respects. 



Of the parts auxiliary to the Eye. 



Above the upper margin of the orbit, on the prominences of 

 the os frontis, called superciliary ridges, the adipose membrane 

 is commonly more full than it is in the other contiguous places ; 

 and the skin which covers it is thereby rendered prominent. 



The supercilia or eyebrows grow out of this prominent skin. 

 The hairs which compose them are placed obliquely, with their 

 roots towards the nose., Their principal use seems to be to 

 defend the eye from sweat and other matters which roll down 

 the forehead. They are moved by the corrugator muscle, and 

 thus express certain passions ; and they are also moved by the 

 occipito-frontalis and orbicularis palpebrarum. 



The extent and degree of curvature of the eyebrows, differ 

 much in different individuals. The hairs of which they are 

 composed, are short, curved, highly elastic, and arranged in 

 VOL. ii. 34 



