

ORBITAL REGION. 245 



The Superior Oblique is a fusiform muscle, placed at the upper and inner side 

 of the orbit, internal to the Levator palpebrae. It arises about a line above the 

 inner margin of the optic foramen, and, passing forwards to the inner angle of the 

 orbit, terminates in a rounded tendon, which passes through a fibre-cartilaginous 

 ring, attached by fibrous tissue to a depression beneath the internal angular pro- 

 cess of the frontal bone, the contiguous surfaces of the tendon and ring being lined 

 by a delicate synovial membrane, and inclosed in a thin fibrous investment. The 

 tendon is reflected backwards and outwards 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. 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 back- 

 wards 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, and 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 palpebra3, 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 anta- 

 gonist 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 in- 

 wards, or downwards and outwards. The movement of circumduction, as in 

 turning the eyes round a room, is performed by the alternate 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 eye- 

 ball 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. 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 de- 

 formity produced in either case is considerable, and is easily remedied by division of one or the 

 other muscle. This operation is readily effected by having the lids well separated by retractors 

 held by an assistant ; 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 conjunctiva covering it divided by a pair of blunt- 

 pointed scissors. Or the tendon may be divided by a sub-conjunctival incision, one blade of the 



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

 M. D. " Anatomical and Physiological Observations." 



