MUSCLES OF THE ORBIT 



1067 



chiefly muscles and fat, and its posterior pole is situated midway between 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 medial and lateral orbital margins usually cuts the eye 

 behind the cornea — laterally behind the ora serrata, medially further forward, at 

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

 ous bands of connective tissue. The lacrimal gland lies under the lateral part of 

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

 orbital 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. 

 SLx muscles, viz., the four recti, the superior oblique, and the levator palpebrae 

 superioris, arise at the apex of the orbit, and diverge as they pass forward. The 

 recti muscles — superior, inferior, lateral, and medial — run each near the corre- 



FiG. 809. — Horizontal Section of the Orbital Region, Viewted From Above. 

 Nasal septum 



Nasal fossa 

 / Infundibulum 



Ethmoidal cells 

 / Medial wall of orbit 



Palpebra superior 

 Cornea 



'^;i\ - Ciliary processes 



•^p^;-r; — "^1- Medial rectus 



— T- Lateral wall of orbit 



"jaHB^SW^r Lateral rectus 

 " Optic nerve 



sponding orbital wall, but the superior is overlapped in part by the levator pal- 

 pebrae. The superior oblique lies about midway between the superior and medial 

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

 anterior part of the orbit, coming from its medial wall and passing below the globe 

 between the termination of the inferior rectus and the orbital floor. The optic 

 nerve with its sheaths passes from the optic foramen to the back of the eyeball, 

 surrounded ,by the orbital fat, and more immediately by a loose connective tis- 

 sue. Among the contents of the cavity are also to be enumerated many vessels 

 and nerves and fibrous tissue septa, while its walls are clothed by periosteum 

 (periorbita). 



The muscles of the orbit are seven in number, of which six are ocular, i. e., are inserted into 

 the eyeball and rotate it in different directions. These ocular muscles are arranged in opponent 

 pairs, viz., superior and inferior recti, superior and inferior obliques, lateral and medial recti. 

 With the exception of the short inferior oblique, they all arise from the back of the orbit along 

 with the seventh orbital muscle, the levator palpebrae superioris. All these long muscles take 

 their origin from the periosteum in the vicinity of the optic foramen. The four recti muscles 

 arise from a fibrous ring, the annulus tendineus communis, which arches close over the upper 



