THE ORBITAL REGION 371 



The orbital muscle, or Muller's muscle (musculus orbitale), which spans the 

 sphenomaxillary fissure and infraorbital groove, is composed of nonstriated 

 fibres, and is a rudimentary structure continuous with the periosteum of the orbit. 1 



Nerves. The Levator palpebrae, Inferior oblique, and all the Recti excepting the External 

 are supplied by the oculomotor nerve; the Superior oblique, by the trochlear; the External 

 rectus, by the abducent. 



Actions. The Levator palpebrae raises the upper eyelid, and is the direct antagonist of the 

 Orbicularis palpebrarura. The four Recti muscles are attached in such a manner to the globe 

 of the eye that, acting singly, they will turn its corneal surface either upward, downward, inward, 

 or outward, as expressed by their names. The movement produced by the Superior or Inferior 

 rectus is not quite a simple one, for, inasmuch as they pass obliquely outward and forward to the 

 eyeball, the elevation or depression of the cornea must be accompanied by a certain deviation 

 inward, with a slight amount of rotation. These latter movements are corrected by the Oblique 

 muscles, the Inferior oblique correcting the deviation inward of the Superior rectus, and the 

 Superior oblique that of the Inferior rectus. The contraction of the External and Internal 

 recti, on the other hand, produces a purely horizontal movement. If any two contiguous Recti 

 of one eye act together, they carry the globe of the eye in the diagonal of these directions 

 viz., upward and inward, upward and outward, downward and inward, or downward and out- 

 ward. The movement of circumduction, as in looking around a room, is performed by the alter- 

 nate action of the four Recti. The Oblique muscles rotate the eyeball on its antero-posterior axis, 

 this kind of movement being required for the correct viewing of an object when the head is moved 

 laterally, as from shoulder to shoulder, in order that the picture may fall in all respects on the 

 same part of the retina of either eye. Sometimes the corresponding Recti and sometimes the 

 opposite ones of the two eyes act together; for instance, the two Superior and Inferior recti carry 

 both eyeballs upward and downward, respectively. In looking toward the right, the right Exter- 

 nal and left Internal recti act together, the reverse being the case in looking toward the left. In 

 turning both eyes toward the middle line, as in directing our vision toward an object less than 

 twenty feet distant, the two Internal recti act together. 



Fasciae of the Orbit. The connective tissue of the orbit is in various places condensed into 

 thin membranous layers, which may be conveniently described as (1) the orbital fascia; (2) the 

 sheaths of the muscles; and (3) the fascia of the eyeball. 



1. The Orbital Fascia. This forms the periosteum of the orbit. It is loosely connected to 

 the bones, from which it can be readily separated. Behind, it is connected with the dura by 

 processes which pass through the optic foramen and sphenoidal fissure, and with the sheath of 

 the optic nerve. In front it is connected with the periosteum at the margin of the orbit, and 

 sends off a process which assists in forming the palpebral fascia or orbital septum. From its 

 internal surface two processes are given off one to enclose the lacrimal gland, the other to 

 hold the pulley of the Superior oblique muscle in position. A layer of nonstriated muscle, the 

 orbital muscle of H. Muller, spans the sphenomaxillary fissure and stray fibres of nonstriated 

 muscle extend along the periosteum of the lateral wall of the orbit. 



2. The Sheaths of the Muscles. The sheaths of the muscles give off expansions to the 

 margins of the orbit which limit the action of the muscles. 



3. The Fascia of the Eyeball. Tenon's capsule surrounds the posterior two-thirds of the 

 eyeball; it will be described with the anatomy of the eyeball. 



Applied Anatomy. The position and exact point of insertion of the tendons of the Inter- 

 nal and External recti muscles into the globe should be carefully examined from the front of 

 the eyeball, as the surgeon is often required to divide the one or the other muscle for the cure 

 of strabismus (squint). In convergent strabismus, which is the more common form of the disease, 

 the eye is turned inward, requiring the division of the Internal rectus. In the divergent form 

 which is more rare, the eye is turned outward, the External rectus being especially implicated. 

 The deformity produced in either case is to be remedied by division of one or the other muscle. 

 The operation is thus performed: The lids are to be well separated; the eyeball being rotated 

 outward or inward, the conjunctiva should be raised by a pair of forceps and divided immedi- 

 ately beneath the lower border of the tendon of the muscle to be divided, a little behind its 

 insertion into the sclera; the submucous areolar tissue is then divided, and into the small aper- 

 ture thus made a blunt hook is passed upward between the muscle and the globe, and the 

 tendon of the muscle and conjunctiva covering it divided by a pair of blunt-pointed scissors. 

 Or the tendon may be divided by a subconjunctival incision, one blade of the scissors being 

 passed upward between the tendon and the conjunctiva, and the other between the tendon and 

 the sclera. Inflammation of the synovial membrane lining the trochlea of the Superior oblique 

 may lead to the formation of a cyst of considerable size. 



1 See F. Groyer, in the Vienna Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften, 1903, Band 

 cxii. 



