210 



THE ANATOMY OF THE HORSE. 



optic nerve. In fomi it is funnel-shaped, forming a kind of sheath t 

 the optic nerve ; but frequently it is divided into four distinct fascicul 



Fig. 23. 



Muscles of the Eyeball. 



1. Inferior oblique ; 2. Inferior rectus ; 3. External rectus ; 4. Internal rectus ; 5. Superior rectus 

 6, 6. Retractor ; 7. Nerve to inferior oblique. 



one lying beneath each of the recti. Its origin is from the margin c 

 the optic foramen, and it is inserted into the sclerotic. 



The Superior Oblique, or Trochleaeis, has a remarkable dispositior 

 It arises at the back of the orbit, and passes inwards to a fibrous arcl 

 or pulley, through which it plays at the inner wall of the orbit, belo 

 the root of the supraorbital process. Having passed through this arcl 

 the muscle is directed outwards above the eyeball ; and it is continue 

 by a tendon which passes beneath the superior rectus to be inserted ini 

 the sclerotic on its outer side, between the insertions of the superic 

 and external recti. 



The Inferior Oblique. This muscle has its origin from the laohr 

 mal fossa at the floor of the orbit. It passes outwards below the ey 

 ball, and becomes inserted into the sclerotic between the insertions of tl 

 inferior and external recti. 



Action of the Muscles of the Eyeball. — The superior and the inferior re 

 tus rotate the eye around a horizontal transverse axis, the former roUir 

 it upwards, the latter downwards. The external and the internal re 

 tus rotate the eye around a vertical axis;-the first rolling it outward 

 the second inwards. The oblique muscles rotate the eye around i 



