THE OEBIT 241 



Its sides are thickened, especially in front, where 

 they give origin to the roots of the fifth, seventh, 

 and eighth cerebral nerves : immediately above these 

 roots, and below the posterior projectioi^of the cere- 

 bellum, the medulla is produced into a pair of large 

 lateral wing-like processes, the restiform bodies, 

 which are connected together in the median plane 

 beneath the overhanging cerebellum. 



B. The Orbit. 



This should 6« examined before the ddssection of the nerves 

 is proceeded with. If the eyelids have been removed as 

 directed above, no further dissection is necessary. Wash out 

 the blood-clots from the orbital sinus with a stream of water, 

 a/voiding injury to the nerves. 



1. The eyeball is almost hemispherical in shape, its outer 



or corneal surface being very flat. 



2. The eye-muscles, by which the movements of the eye 



are effected, are six narrow muscular bands which 

 arise from the skull-wall and are inserted into the 

 eyeball : they are arranged in two groups. 



a. The recti muscles' are four in number. They arise 

 close together, near the hinder end of the orbit, and 

 diverge outwards to be inserted into the eyeball. 



i. The rectus superior runs outwards and forwards 

 to be inserted iato the dorsal surface of the 

 eyeball. 



ii. The rectus internus, or anterior, runs forwards 

 between the skull- wall and the eyeball, and is 

 inserted into the anterior surface of the eyeball. 



iii. The rectus externus, or posterior, is the hind- 

 most of the eye-muscles, and runs directly 

 outwards behind the eyebaU, to be inserted 

 into its posterior surface. 



iv. The rectus Inferior runs outwards and forwards 

 beneath the eyeball, and is inserted into its 

 ventral surface. 



