II50 A MANUAL OF ANATOMY 



prolonged forwards into the inferior tendon or ligament of Zinn, 

 which gives origin from within outwards to part of the internal 

 rectus, the inferior rectus, and the inferior head of the external 

 rectus. 



Obliqui Muscles — Superior Oblique — Origin. — ^The wall of the 

 orbit directly in front of the upper and inner part of the optic 

 foramen, where it is contiguous to the superior and internal recti. 



Insertion. — By an expanded tendon into the upper and outer 

 aspect of the sclerotic, just beyond the outer border of the superior 

 rectus, and midway between the margin of the cornea and the 

 entrance of the optic nerve. 



The muscle is situated at the upper and inner part of the orbit, 

 internal to the levator palpebrae superioris. It is directed forwards 

 towards the inner angle of the orbit, on approaching which it ends 

 in a small round tendon. This tendon passes over a fibro-cartila- 

 ginous pulley or trochlea, close to the internal angular process of 

 the frontal bone. Thereafter it changes its direction, and passes 

 downwards, outwards, and backwards beneath the tendon of the 

 superior rectus to reach its insertion just external to that tendon. 



The fibro- cartilaginous pulley or trochlea is attached by fibrous 

 tissue to the fovea trochlearis on the orbital plate of the frontal 

 bone close to the internal angular process. It is lined with synovial 

 membrane to lubricate the tendon and facilitate its movement at 

 this abrupt change in its course. The tendon receives a fibrous 

 investment from the outer margin of the pulley. 



Nerve-supply. — ^The fourth cranial nerve, which enters the muscle 

 on its superficial or orbital surface near its origin. 



Action. — ^To depress and abduct the eyeball, or turn it outwards, 

 the eyeball being at the same time slightly rotated. 



Relations — Superior. — ^The roof of the orbit and the superior 

 rectus. Inferior. — ^The upper border of the internal rectus, with 

 the intervention of the nasal nerve, and the anterior and posterior 

 ethmoidal vessels. External. — ^The levator palpebrse superioris. 



Inferior Oblique — Origin. — A small depression at the anterior and 

 inner part of the floor of the orbit, immediately external to the 

 upper opening of the lachrymal canal. 



Insertion. — ^The outer surface of the sclerotic under cover of the 

 external rectus, and slightly posterior to the level of the insertion 

 of the superior oblique. 



Nerve-supply. — ^The lower division of the third cranial nerve, the 

 branch of which is long and enters the posterior border of the muscle. 



The muscle at first passes outwards and backwards upon the 

 floor of the orbit beneath the inferior rectus, and then it turns up- 

 wards between the sclerotic and the external rectus, where its 

 tendon expands before taking insertion. 



Action. — To elevate and abduct the eyeball, which is at the same 

 time slightly rotated. 



Relations. — Towards the eyeball the muscle is related to the 

 inferior rectus and the sclerotic, and towards the orbit to the floor 



