THE ORGAN OF SIGHT. 4II 
4. Muscles of the Orbit (Fig. 166).—Within the orbit are 
eleven muscles, ten connected with the eyeball, and one, 
M. levator palpebrz superioris, with the upper eyelid. 
Of the ten muscles ofthe eyeball, eight are straight 
muscles, passing from an origin about the inner end of the 
orbit directly distad; the other two have an oblique direction. 
Four of the straight muscles are larger and are known as the 
Mm. recti (4, c, @); these are distinguished according to their 
position as lateral (c), medial, superior (7), and inferior (4). 
The four smaller straight muscles constitute together M. re- 
tractor oculi (¢). The two oblique muscles are known as 
Mm. obliqui and are distinguished according to their position 
as inferior (a) and superior. 
Fic, 166.—MuscLes oF THE EYEBALL, LATERAL VIEW. 
a, M. obliquus inferior; 4, M. rectus inferior; ¢, M. rectus lateralis; ¢, M. rectus 
superior; ¢, parts of M. retractor oculi; 7, the oculomotor nerve. 
Mm. recti (4, c, @).—The four recti muscles arise from the 
bone about the optic foramen and pass toward the eyeball. 
They are inserted by thin, flat tendons along a line which 
separates the darker caudal part of the sclerotic from the white 
zone of the sclerotic which borders the cornea,—the line of 
insertion of the four tendons forming thus a circle about the 
eyeball. The rectus superior (d7) is partly covered by M. 
levator palpebrz superioris. The tendon of the rectus inferior 
(4) is crossed by M. obliquus inferior (2). The recti muscles 
are all innervated by the oculomotor (third) nerve (/), except 
the lateral (c), which is supplied by the abducens (sixth) nerve. 
M. retractor oculi (¢).—The retractor oculi arises about the 
optic foramen and divides into four heads which lie nearer the 
