102 ANIMAL MECHANISM. 



h Levator occuli, or superior straight muscle, to roll the ball 



upward. 



i ibductor occuli, rolls the ball outward. 



k Adductor occuli, rolls it towards the nose. 



/ Depressor occuli, rolls the ball downward, towards the cheek. 



m The superior oblique muscle, passing through a loop at n. 



n Called the trochlea, or pully, but, in fact, a simple loop. 



o Insertion of the superior oblique muscle in the eye-ball. 



p The inferior oblique muscle, taking its rise from a bone. 



q The insertion of the tendon of the inferior oblique muscle in the 



first coat of the ball. 



COATS OP THE EYE. 



Such is the mechanical arrangement of the different 

 coats or coverings of the eye, answering in use, to the 

 brass tubes of a spy-glass, that one is fitted within the 

 other, like a nest of boxes : they are three in number. 

 Anatomists, however, make minute subdivisions of these, 

 of no practical benefit to themselves or others. 



Explanation of Figure 2. FlG - 2 - 



This is a plan of the coats, or 

 as they are termed in anatomical 

 works, tunics. 



Reference should be made to 

 this after reading the text. The 

 natural figure of the eye, in out- 

 line, is preserved. 



a The Sclerotic, or first hard 

 tunic. 



b The Choroid, or fleecy tunic. 



c The Retina, or third and in- 

 most tunic, which is an expan- 

 sion of the optic nerve g the certain seat of vision. 



d The Cornea, or prominent, transparent circle, over which the 

 lids close, in winking, hereafter to be described. 



e The Crystalline lens, or little magnifying glass of the eye, 

 about a quarter of an inch in diameter. 



/Is the space filled by one of the fluids of the eye, and 

 called the anterior chamber. 



g The stump of the optic nerve, which is prolonged into the sub- 

 stance of the brain. 



