256 HEAD AND NECK 



arches, a superior and an inferior. Both are attached later- 

 ally to a projection on the great wing of the sphenoid bone 

 at the lateral margin of the superior orbital fissure. The two 

 bands diverge from one another as they pass medially across 

 the superior orbital fissure, the upper band extending to the 

 superior margin, and the lower to the inferior margin of the 

 optic foramen. The superior rectus, which is the thinnest of 

 the four recti, springs from the medial part of the upper 

 band ; the inferior rectus, which is thicker but smaller than 

 the superior, springs from the middle part of the lower band. 

 The lateral and longest rectus, which is thicker than either the 

 superior or inferior, arises by two heads, one from the lateral part 

 of the upper band, and one from the lateral part of the lower 

 band. The interval between the two heads is traversed by the 

 two divisions of the oculo-motor nerve, the naso-ciliary nerve, 

 the abducens nerve, and the ophthalmic veins. The medial 

 rectus, which is the shortest and thickest of all the recti, 

 springs from the medial part of the lower band. The superior 

 oblique springs from the body of the sphenoid, between the 

 superior and medial recti. The origin of the inferior oblique 

 lies near the anterior margin of the orbital cavity, entirely 

 away from the other muscles which move the eyeball. It 

 arises from the orbital plate of the maxilla close to the lower 

 and medial angle of the orbital cavity. 



Dissection. To display the attachments of the ocular muscles 

 which arise at the apex of the orbital cavity divide the optic 

 nerve close to the optic foramen, and turn the eyeball forwards. 

 Then define the origin of each muscle, but take care not to 

 injure the structures which pass between the upper and lower 

 heads of the lateral rectus. Next, replace the eyeball in position 

 and display the inferior oblique which lies in the anterior part 

 of the orbital cavity and is best dissected from the front. Evert 

 the lower eyelid and make an incision through the conjunctiva, 

 along the level of its reflection from the eyelid to the eyeball. 

 A little dissection in the floor of the anterior part of the orbit 

 and the removal of some fat will expose the inferior oblique 

 muscle, as it passes laterally and backwards to gain the lateral 

 surface of the sclera. 



After the origins of the muscles have been satisfactorily 

 displayed study first the arrangement of the nerves which pass 

 through the superior orbital fissure, next the insertions of the 

 muscles which move the eyeball, and finally the remaining 

 structures which lie in the orbital cavity. 



Arrangement of the Nerves in the Superior Orbital 

 Fissure. The various nerves met with in the dissection of 



