398 THE MUSCLES AND FASCIA. 



maxillary bone, external to the lachrymal groove for the nasal duct. Passing out- 

 ward, backward, and upward beneath the Inferior rectus, and then between the 

 eyeball and the External rectus, it is inserted into the outer part of the sclerotic 

 coat between the Superior and External recti, near to, but somewhat behind, the 

 tendon of insertion of the Superior oblique. 



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

 rectus ; by its orbital surface, with the periosteum covering the floor of the orbit, 

 and with the External rectus. Its borders look forward and backward ; the 

 posterior one receives a branch of the third nerve. 



Nerves. The Levator palpebrae, 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 palpebrge 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 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, which, however, is 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 con- 

 traction 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, thev 

 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 outward. 

 The movement of circumduction, as in looking round a room, is performed by 

 the alternate 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 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 the one or the other muscle for the cure 

 of strabismus. 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 immediately 

 beneath the lower border of the tendon of the muscle to be divided, 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 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 

 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 opposite side the operation may be performed. 



5. Nasal Region (Fig. 269). 



Pyramidalis nasi. t Dilatator naris anterior. 



y Levator labii superioris algeque nasi. f Compressor nasi. 



j Dilatator naris posterior. ^ Compressor narium minor. 



v ' Depressor alge nasi. 



1 " On the Oblique Muscles of the Eye in Man and Vertebrate Animals," by John Struthers, M. D., 

 in Anatomwal and Physiological Observations. For a fuller account of the various co-ordinate actions 

 of the muscles of a single eye and of both eyes than our space allows, the reader may be referred to 

 Dr. M. Foster's Teal-book of Physiology. 



