854 



ORG ASS OF SPECIAL SEXSE 



CAVITY OF THE ORBIT 



General Arrangement of its Contents 



The anterior wider half of the cavity is mainly occu])ie<l by the eyel)all, -which 

 lies almost axially, but is rather nearer to the upper and outer than it is to the 

 other walls. The posterior two-thirds of the globe are in relation with soft parts, 

 chiefly muscles and fat, and its posterior pole is situated midway lietween the base 

 (or opening) and the apex of the orbital cavity. The anterior third of the eye- 

 ball is naturally free, except for a thin covering of the conjunctiva, and projects 

 slightly beyond the opening of the orbit, the degree of prominence varying with 

 the amount of orbital fat, and also to some extent with the length of the globe. A 

 straight line joining the inner and outer orbital margins usually cuts the eye behind 

 the cornea — externally behind the ora serrata, nasally further forward, at the 

 junction of the ciliary body and iris. The globe is held in position by numerous 

 bands of connective tissue. The lachrymal gland lies under the outer part of the 



Fig. 481. — Left Eyebai.l seen in its Normal Position in the Orbit, with Yikw 

 OF THE Ocular Muscles. (After Merkel, uuHlified.) 



Tendon of superior oblique 



Levator palpebrae super- 



ioris, cut 

 Superior rectus 



Inernal rectus 



Inferior oblique muscle 



External rectus 



Inferior rectus 



roof of the orbit anteriorly. The orbital fat occupies the spaces between the orl)ital 

 muscles, and is in greatest amount immediately behind the eyeball; it also exists 

 between the muscles and the orbital walls in the anterior half of the cavity. Six 

 muscles, viz. the four recti, the superior oblique, and the levator pali)ebr£e supe- 

 rioris, arise at the apex of the orbit, and diverge as they pass forwards. The recti 

 muscles — superior, inferior, external, and internal — run each near the correspond- 

 ing orl)ital wall, but the superior is overlapped in part by the levator palpebne. 

 The superior oV)li(|ue lies about midway between the superior and internal recti. 

 A seventh muscle, the inferior oblique, has a short course entirely in the anterior 

 part of the orbit, coming from its inner wall and passing beneath the globe ])etween 

 the termination of the inferior rectus and the orbital floor. The optic nerve with 

 its sheaths passes from the o])tic foramen to the back of the ej'-eball, surrounded by 

 the orbital fat, and more immediately by a loose connective tissue. Among the 

 contents of the cavity are also to he enumerated many vessels and nerves, and 

 flbrous tissue septa, Avhile its walls are clothed by periosteum (periorbita). 



The muscles of the orbit are seven in number, of which six are omhtr, i.e. arc 

 inserted into the eveljall and rotate it in different directions. Tliese ocular muscles 



