ORBITAL REGION. 323 



beneath the Superior Rectus to the outer part of the globe of the eye, and is 

 inserted into the sclerotic coat, midway between the cornea and entrance of 

 the optic nerve, the insertion of the muscle lying between the Superior and 

 External Recti. 



Relations. By its upper surface, with the periosteum covering the roof of 

 the orbit, and the fourth nerve. The tendon, where it lies on the globe of the 

 eye, is covered by the Superior Rectus. By its under surface, with the nasal 

 nerve, and the upper border of the Internal Rectus. 



The Inferior Oblique is a thin, narrow muscle, placed near the anterior margin 

 of the orbit. It arises from a depression in the orbital plate of the superior 

 maxillary bone, external to the lachrymal groove. Passing outwards and 

 backwards beneath the Inferior Rectus, and between the eyeball and the 

 External Rectus, it is inserted into the outer part of the sclerotic coat between 

 the Superior and External Rectus, near the tendon of insertion of the Superior 

 Oblique. 



Relations. By its upper surface, with the globe of the eye, and with the 

 Inferior Rectus. By its under surface, with the periosteum covering the floor 

 of the orbit, and with the External Rectus. Its borders look forwards and 

 backwards ; the posterior one receives a branch of the third nerve. 



Nerves. The Levator Palpebrse, Inferior Oblique, and all the Recti excepting 

 the External, are supplied by the third nerve ; the Superior Oblique, by the 

 fourth ; the External Rectus, by the sixth. 



Actions. The Levator Palpebrae raises the upper eyelid, and is the direct 

 antagonist of the Orbicularis Palpebrarum. The four Recti muscles are 

 attached in such a manner to the globe of the eye, that, acting singly, they 

 will turn it either upwards, downwards, inwards, or outwards, as expressed by 

 their names. If any two Recti act together, they carry the globe of the eye 

 in the diagonal of these directions, viz., upwards and inwards, upwards and 

 outwards, downwards and inwards, or downwards and outwards. The move- 

 ment of circumduction, as in looking round a room, is performed by the alter- 

 nate action of the four Recti. By some anatomists, these muscles have been 

 considered the chief agents in adjusting the sight at different distances, by 

 compressing the globe, and so lengthening its antero-posterior diameter. 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 each eye. 1 



Surgical Anatomy. The position and exact point of insertion of the tendons of the Internal 

 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 one or the other muscle for the cure of stra- 

 bismus. In convergent strabismus, which is the most common form of the disease, the eye is 

 turned inwards, requiring the division of the Internal Rectus. In the divergent form, which is 

 more rare, the eye is turned outwards, 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 effected : the lids are to be well separated ; the eyeball being drawn outwards, 

 the conjunctiva should be raised by a pair of forceps, and divided immediately beneath the lower 

 border of the tendon of the Internal Rectus, a little behind its insertion into the sclerotic ; the 

 submucous areolar tissue is then divided, and into the small aperture thus made, a blunt hook 

 is passed upwards between the muscle and the globe, and the tendon of the muscle and con- 

 junctiva 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 upwards between the tendon 

 and the conjunctiva, and the other between the tendon and the sclerotic. The student, when 

 dissecting these muscles, should remove on one side of the subject the conjunctiva from the 

 front of the eye, in order to see more accurately the position of the tendons, while on the op- 

 posite side the operation may be performed. 



1 " On the Oblique Muscles of the Eye in Man and Vertebrate Animals" by JOHN STRUTTHERS, 

 M. D., " Anatomical and Physiological Observations" 



