108 ANIMAL MECHANISM. 



FIG. 4. 



Explanation of Figure 4. 

 This plan presents a longitudinal section of the left eye and bony 



orbit. 



a The upper eye-lid, shut 



b The cornea. 



cc The cut edges of the iris. 



d The pupil or round hole through the centre of the iris, which, in 

 the living eye, resembles a black, highly polished dot. 



te The cut edges of the sclerotic and choroid tunics, with the 

 retina, before exhibited in the preceding drawings. 



f The crystalline Zens, as it is lodged, with reference to other parts. - 



gg The Ciliary processes continued from the choroid coat. The 

 plaits are here distinctly seen. In other designs accompanying 

 this article, they will be noticed in a front view. 



h The optic nerve running from the brain, through the bones, to 

 the globe of the eye, apparently closely embraced by the recti, 

 or straight muscles. 



The levator, or muscle that raises the upper eye-lid. 



k The upper straight muscle of the eye, called levator occult. 



I Inferior straight muscles, its antagonist, on the under side of the 

 ball, called depressor occuli. 



m A section of the infeiior oblique muscle, called obliquus infe- 

 rior, used in rolling the eye upward and inward, as in looking ai 

 a button laid above the root of the nose. The superior oblique, 

 passing through a loop, carries the eye downward and outward, as 

 in looking at the top of the shoulder. These two muscles, 

 by old writers, were termed rotatores and amatores, in allusion to 

 their office of rolling the ball and expressing passions. 



nn A section of the blood vessels and nerves, with a large quan- 

 tity of fat, surrounding the optic nerve. This fat lies between the 

 muscles and betwixt the socket and globe. 



