! 



Mammalia. 153 



inserted in the lower surface of the eyeball ; this is the inferior 

 oblique muscle. 



4. Four straight muscles, the superior rectus, inferior rectus, 

 internal rectus, and external rectus, are attached to the top, bot- 

 tom, and sides of the eyeball ; find the origin of these, with that 

 of the superior oblique, at the bottom of the eye socket. 



5. Dissect away the fat and other tissue around these muscles, 

 and find a cone-shaped muscle attached to the back of the eye. 

 Within this find the cylindrical optic nerve. 



External Parts of the Eye. The eye of the rabbit may be 

 used, but that of the ox is better. 



1 . Observe the clear front part of the eye, the cornea. Note 

 its shape. Its wider end was at the inner angle of the eyelids. 



2. Around the cornea find a whitish membrane, the conjunctiva, 

 which, a short distance back from the cornea, separates from 

 the eyeball to turn forward, and line the eyelid. 



3. The several muscles of the eyeball, a mass of fat which 

 forms a cushion for the eye, and other tissue, should be trimmed 

 away, leaving the optic nerve. 



4. Place the eye in its natural position, and make drawings 

 of it, as seen from the front and from one side, naming the 

 parts. 



Dissection of the Eye. Beef eyes are of good size for dis- 

 section. Each member of the class should have an eye to 

 dissect. To supply a large class it is best to send to a slaugh- 

 tering house in the nearest large city. If the eye muscles and 

 other external parts have already been studied, it will not be 

 necessary to remove the muscles and fat around the eye ; in 

 fact, they may well be left untouched, as they serve as a cushion 

 to support the eye during dissection. The eye may be con- 

 veniently dissected on a small piece of board or shingle ; and 

 if it is desirable to turn the eye, it is better to do so by turning 

 the support, as the eye usually sticks to the support and the dis- 

 section may be injured by trying to move it. 



CAUTION. After the eye is opened be careful not to compress 



