ORBITAL FASCIA 



1071 



The chief action of the superior rectus is to draw the cornea upward, but at the same time 

 it adducts and rotates the cornea medially. 



The inferior rectus mainly draws the cornea downward, also adducting it and rotating it 

 laterally. 



The chief action of the superior oblique is to rotate the cornea medially, also drawmg it 

 downward and slightly abducting it. 



The inferior oblique mainly rotates the cornea laterally, also drawing it upward and slightly 

 abducting it. 



The fasciae of the orbit [fasciae orbitales]. — The orbital contents are bound to- 

 gether and supported by fibrous tissues, which are connected with each other, but 

 which may conveniently be regarded as belonging to three systems. These are : — 

 (1) Those hning the bony walls; (2) those ensheathing the muscles; and (3) the 

 tissue which partially encapsules the eyeball. 



1. The orbital periosteum [periorbita], is closely applied to the bones forming 

 the walls of the cavity, but may be stripped off with comparative ease. It pre- 

 sents openings for the passage of vessels and nerves entering and leaving the orbit. 



Fig. 815. — Diagram Representing the Orbital FASCise in Vertical Section. Periorbita 

 black; muscular sheaths violet; Tenon's capsule green. 

 . M. orbicularis oculi 



• Periorbita and septum orbitale 

 ii>^^_ / / Anterior insertion of levator palpebrae 



•'^V_^-;.-;*?^^Si>r--<;j>^ ^ Process from periorbita to sheath of lacrimal gland 

 Sheath of levator palpebrae 



Periorbita 



>^M. levator palpebrse superioris 



^X^^M. rectus superior 



Space filled by orbital fat 



Fascial sheath of optic 

 nerve 

 Optic nerve 



^ M. rectus inferior 



M. obliquus inferior 



Posteriorly this tissue is very firm, being joined by processes of the dura mater at the optic 

 foramen and superior orbital fissure; at the optic foramen it is also connected with the dura 

 sheath of the optic nerve. As it covers the inferior orbital (spheno-maxiUary) fissure its fibres 

 are interwoven with smooth muscle, forming the orbital muscle of MtiUer. From its inner sur- 

 face processes run into the orbital cavity, separating the fat lobules. One important process 

 comes from the periorbita about midway along the roof of the orbit, runs forward to the back of 

 the upper division of the lacrimal gland, and there splits, helping to form the gland-capsule: 

 this capsule is joined at its medial border by other periorbital bands coming off near the upper 

 orbital rim, and forming the suspensory ligament of the gland. On the side of the orbit the peri- 

 orbita sends fibrous processes to the trochlea of the superior obhque, which keep it in position. 

 On arriving at the lacrimal groove the periorbita divides into two layers, a thin posterior one 

 continuing to line the bone forming the floor of the groove, whilst the thicker anterior layer 

 bridges over the groove and the sac which Ues in it, forming the limbs of the medial palpebral 

 ligament (p. 1052). 



Quite anteriorly, at the rim of the orbit, the periorbita sends off a membranous process which 

 aids in forming the fibrous tissue of the eyelids (orbito -tarsal ligament, or palpebral fascia), 

 and is itself continuous with the periosteum of the bones outside the orbital margin. 



2. The orbital muscles are connected b}^ a common fascia, which splits at their 

 borders and furnishes a sheath to each. Processes of this fascia give membranous 

 investments for the vessels and nerves (including the optic nerve), splitting simi- 



