180 



MUSCLES OF THE HEAD AND NECK. 



(trochlea) attached to the fovea trochlearis of the frontal bone ; it is there 

 reflected outwards and backwards, and passes between the eye and the 

 superior rectus to be inserted into the sclerotic coat midway between the 

 superior and external recti muscles, nearly equidistant from the cornea and 

 the entrance of the optic nerve. A sy no vial sheath lines the contiguous 

 surfaces of the tendon and pulley. 



This muscle is covered by the roof of the orbit, the fourth nerve entering its upper 

 surface ; and beneath it lie the nasal nerve and the internal rectus muscle. 



Fig. 157. 



r ~ I 



Fig. 157. A, VIEW OF THE MUSCLES 

 OP THE RIGHT ORBIT, PROM THE 

 OUTSIDE, THE OUTER WALL HAVING 

 BEEN REMOVED. 



B, EXPLANATORY SKETCH OP THE SAME 



MUSCLES. 



a, supraorbital ridge ; b, lower margin 

 of the orbit formed by the superior max- 

 illary bone ; c, anterior clinoid process ; 



d, posterior part of the floor of the 

 orbit above the spheuo-maxillary fossa ; 



e, side of the body of the sphenoid 

 bone below the optic foramen and sphe- 

 noidal fissure ; /, sinus maxillaris ; 

 1, anterior part of levator palpebrse 

 superioris, where it is inserted into 

 the eyelid ; 2, pulley and tendon of the 

 superior oblique muscle ; 3, tendon of 

 the superior rectus muscle at its inser- 

 tion upon the eyeball ; 4, in A, outer 

 surface of the external rectus ; 4 , in B, 

 the anterior or inserted tendon of the 

 same muscle, a part of which has been 

 removed ; the double origin of the muscle 

 is shown at the apex of the orbit ; 5, 

 the inferior oblique muscle crossing the 

 eyeball below the inferior rectus ; 6, the 

 inferior rectus ; 7, in B, the inside of 

 the internal rectus, seen in consequence 

 of the removal of a part of the external 



rectus, and near it, the end of the optic nerve cut short close to the place of its entrance 

 into the eyeball. 



The inferior oblique is the only muscle of the eye which does not take 

 origin at the apex of the orbit. It arises from a minute depression in 

 the orbital plate of the superior maxillary bone, just within the anterior 

 margin of the orbit, and close to the external border of the lachrymal 

 groove. The muscle inclines outwards and backwards between the inferior 

 rectus and the floor of the orbit, and ends in a tendinous expansion, which 

 passes between the external rectus and the eyeball, to be inserted on the 

 external and posterior aspect of the globe. 



ACTIONS. The recti muscles turn the eye upwards, downwards, and from side to 

 side, thus placing the axis of the eye in these or any intermediate directions. Evidence 

 is against the supposition that the recti muscles are capable of altering the position of 

 the eyeball in an antero-posterior direction, nor is it probable that they can in any 

 perceptible degree change its form. (Jacob, " On Paralytic, Neuralgic, and other 

 Nervous Diseases of the Eye," in "Dublin Med. Press," 1841 ; G. Johnson, the article 

 "Orbit," in "Todd's Cyclopaedia of Anatomy and Physiology.") For the action of the 

 oblique muscles, see the note on page 501*. 



