412 SENSE-ORGANS AND INTEGUMENT. 
eyeball than the recti and are therefore partly covered by the 
latter. They alternate with the recti and are inserted into 
the eyeball at about its equator, except the inferior division, 
which is inserted on a line with the recti. They are supplied 
by the oculomotor nerve. 
’ M. obliquus inferior (2),.—The inferior oblique arises from 
the maxillary bone just laterad of the lachrymal bone and 
curves over the ventral side of the eyeball along the lines of 
insertion of the recti (crossing the tendon of the rectus inferior, 
6) to the ventral edge of the tendon of the lateral rectus (c), 
where it is inserted. It rotates the eyeball and is supplied by 
the third nerve (/): 
M. obliquus superior.—The superior oblique takes origin 
from the cranial border of the optic foramen, passes dorso- 
craniad, and ends in a small rounded tendon which passes 
through a fibrous pulley-ring. This ring is situated near the 
rim of the orbit, one or two centimeters craniad of the zygomatic 
process of the frontal bone, and is attached to the wall of the 
orbit by two fibrous bands. After passing through the pulley- 
ring the tendon turns and passes laterocaudad; it ‘becomes 
much expanded, passes caudad of the superior rectus, and is 
inserted into the eyeball along the caudal margin of the inser- 
tion of the superior rectus tendon. The superior oblique is 
supplied by the trochlear (fourth) nerve. 
M. levator palpebre superioris.—This is a small thin 
muscle which takes origin on the wall of the optic foramen 
close to the rectus superior, passes over the outer surface of the 
rectus superior and beneath the lachrymal gland, and forms a 
thin tendon which is inserted into the margin of the upper 
eyelid. It is innervated by the oculomotor. 
5. The Eyeball.—The eyeball is approximately spherical 
in form, but the cranial surface has a slightly greater curvature 
than the caudal portion, so that the eye appears slightly pointed 
at the cranial (free) surface. The large cylindrical optic nerve 
(Fig. 167, a) enters the eyeball at nearly the centre of the 
caudal half of the eye. Onthe outer surface is seen the trans- 
parent cornea (c), covering the free surface of the eye, and the 
opaque sclerotic (4), covering the remainder of the ball. 
