276 



MUSCLES OF THE HEAD AND KECK. 



nerve. A synovial sheath lines the contiguous surfaces of the tendon 

 and pulley. 



Bt'lations. — This muscle is covered by the roof of the orbit, the fomth nerve 

 entering its upper siu-face ; and beneath it lie the nasal nerve and the internal 

 rectus muscle. 



Fig. 205. — A View op the Muscles 

 OP THE Eight Okbit, fkoji the 



OUTSIDE, THE OUTEK WALL HAVING 

 BEEX EEMOVED. (A. T.) h 



B, Explanatory Sketch of the sajie 



Muscles. 



a, supraorbital ridge ; h, 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 sphcno-maxillary fossa ; 



e, side of the body of the sphenoid 

 bone below the optic foramen and sphe- 

 noidal fissure ; /, sinus maxillaris ; 

 1, levator palpebraj superioris, near its 

 insertion ; 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, externa\ 

 rectus ; 4', in B, tendon of insertion 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 

 tlie internal rectus, seen in consequence 

 of tlie removal of a part of the external 

 rectus, and near it, the end of the optic 

 nen'e ciTt 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 oritrin at the apex of the orbit. It arises from a minute de- 

 pression 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. 



Varletle.t. — The levator palpebiTC sometimes gives off a slip from its inner 

 border, which passes to be inserted into the trochlea, foiming the tcmor trochlea; 

 of Budge. A slip of a similar natui-e was described by Albinus as a case of 

 doubling of the levator palpebrte, and by Mollinetti as a fifth rectus. The 

 levator palpebrre has been seen entirely wanting (Macalister). 



The rectus esternus may have its two heads separate to their insertion, thus 

 forming a double rectus (Albinus). Macalister has twice noted the absence of 

 the outer head. 



The transversris orhilaji. (EochAslek) consists of an arching slip of muscular 

 fibres passing from the anterior and superior portion of the os planum across 

 the upper surface of the eyeball to the outer wall of the orbit. It is probably, 

 as Macalister suggests, a displaced deep slip of the palpebral fibres of the orbi- 

 cularis palpebrarum. 



