THE ACCESSORY ORGANS OF THE EYE 



1023 



fibrous investment. The tendon is reflected backward, lateralward, and downward 

 beneath the Rectus superior to the lateral part of the bulb of the eye, and is inserted 

 into the sclera, behind the equator of the eyeball, the insertion of the muscle lying 

 between the Rectus superior and Rectus lateralis. 



The Obliquus oculi inferior (inferior oblique) is a thin, narrow muscle, placed near 

 the anterior margin of the floor of the orbit. It arises from the orbital surface of 

 the maxilla, lateral to the lacrimal groove. Passing lateralward, backward, and 

 upward, at first between the Rectus inferior and the floor of the orbit, and then 

 between the bulb of the eye and the Rectus lateralis, it is inserted into the lateral 

 part of the sclera between the Rectus superior and Rectus lateralis, near to, but 

 somewhat behind the insertion of the Obliquus superior. 



Frontal nerve 



Sup. ramus of oculomotor nerve 

 Sup. orbital fissure 

 Lacrimal nerve 



Levator palpebrce super. 

 Nasociliary nerve 

 Trochlear nerve 

 TroMea 



Abducent nerve 



Inf. ramus of oculomotor Inf. orbital 

 nerve -fissure 



\ 



Optic foramen 





FIG. 890. Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure. 



Nerves. The Levator palpebrse superioris, Obliquus inferior, and the Recti superior, inferior, 

 and medialis are supplied by the oculomotor nerve; the Obliquus superior, by the trochleai 

 nerve; the Rectus lateralis, by the abducent nerve. 



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

 Orbicularis oculi. The four Recti are attached to the bulb of the eye in such a manner that, 

 acting singly, they will turn its corneal surface either upward, downward, medialward, or lateral- 

 ward, as expressed by their names. The movement produced by the Rectus superior or Rectus 

 inferior is not quite a simple one, for inasmuch as each passes obliquely lateralward and forward 

 to the bulb of the eye, the elevation or depression of the cornea is accompanied by a certain 

 deviation medialward, with a slight amount of rotation. These latter movements are corrected 

 by the Obliqui, the Obliquus inferior correcting the medial deviation caused by the Rectus superior 

 and the Obliquus superior that caused by the Rectus inferior. The contraction of the Rectus 

 lateralis or Rectus medialis, on the other hand, produces a purely horizontal movement. If any 

 two neighboring Recti of one eye act together they carry the globe of the eye in the diagonal of 

 these directions, viz., upward and medialward, upward and lateralward, downward and medial- 

 ward, or downward and lateralward. Sometimes the corresponding Recti of the two eyes act 

 in unison, and at other times the opposite Recti act together. Thus, in turning the eyes to the 

 right, the Rectus lateralis of the right eye will act in unison with the Rectus medialis of the left 

 eye; but if both eyes are directed to an object in the middle line at a short distance, the two Recti 

 mediales will act in unison. The movement of circumduction, as in looking around a room, is 

 performed by the successive actions of the four Recti. The Obliqui rotate the eyeball on its 

 antero-posterior axis, the superior directing the cornea downward and lateralward, and the 





