gO DISSECTION OF THE EVE, 
portion of this muscle lies to the inside of the internal 
rectus, between it and the inner wall of the orbit; its 
fibres arise round the optic foramen with the recti mus- 
cles, pass outward along the inner wall of the orbit to 
its upper and outer angle, where they end in a slender 
tendon which hes in a groove ina piece of cartilage 
(the trochlea) found at this point. After passing 
through the groove the tendon bends backward to the 
eyeball, and is inserted just beneath the tendon of the 
superior rectus muscle. ‘The trochlea serves as a pul- 
ley to change the direction of the pull of the muscle. 
7, The Retractor Bulbi. Lifting up the four rect 
muscles, or removing them altogether, there will be 
found beneath four slips of much paler muscle, having 
the same general direction as the recti muscles. Taken 
together they form the retractor bulbi, and in some 
mammals are united to form a single hollow muscle 
inserted round the circumferencc of the eyeball. 
DISSECTION'OF THE EYEBALL. 
The dissection of the eyeball can be made upon the 
dog, or perhaps more conveniently upon one of the 
ordinary slaughter-house animals, the eyes of which 
can be obtained very easily from a butcher. Of the 
animals killed by butchers the pig has the best eye 
for dissection. While it is smaller than that of the 
ox or sheep, itis quite large enough to make it easy to 
dissect, and has the advantage of resembling the hu- 
man eye more closely in size and general shape, and 
besides, like the human eye, has no tapetum, so that 
the anatomy of the retina is more clearly seen. The 
following directions are written especially for the pig’s 
eye, though they can be used for the eyes of other 
