346 HEAD AND NECK 



been traced to the rectus superior and the levator palpebrae 

 superioris. The inferior division is larger. It almost im- 

 mediately divides into three branches for the supply of the 

 rectus medialis, the rectus inferior, and the obliquus inferior. 

 The nerves to the two recti enter the ocular surfaces of the 

 muscles ; the nerve to the inferior oblique is prolonged 

 anteriorly, in the interval between the rectus inferior and 

 rectus lateralis, and enters the posterior border of the inferior 

 oblique muscle. Soon after its origin this branch gives the 

 short motor root to the ciliary ganglion. 



Nervus Abducens. The sixth nerve will be found closely 

 applied to the ocular surface of the lateral rectus. It enters 

 the orbit through the narrow interval between the heads of 

 lateral rectus muscle and it supplies this muscle only. 



Arrangement of the Nerves in the Superior Orbital 

 Fissure. When the orbit is dissected, and the various nerves 

 met with in the dissection of the cavernous sinus are traced 

 into the cavity, the dissector will note that the arrangement of 

 the nerves in the superior orbital fissure is somewhat different 

 from that in the sinus. 



The lacrimal, frontal, and trochlear nerves enter the orbit 

 above the muscles on very much the same plane (Fig. 137). 

 The other nerves enter between the heads of the lateral 

 rectus. Of these the superior division of the oculo-motor 

 nerve is the highest, next comes the naso-ciliary nerve, then 

 the inferior division of the oculo-motor nerve, and the 

 abducent nerve occupies the lowest level. 



Dissection. The inferior oblique muscle is placed very differently from 

 the other muscles of the orbit. It is situated below the eyeball, running 

 below its inferior surface to gain its lateral surface. It must be dissected 

 from the front. It is necessary, therefore, to restore the eyeball to its 

 natural place. Next, evert the lower eyelid and remove the conjunctiva 

 from its deep surface as it is reflected on to the globe of the eye. A little 

 dissection in the floor of the anterior part of the orbit and the removal of 

 some fat will reveal the inferior oblique muscle. 



Musculus Obliquus Inferior. This muscle arises from a 

 small depression on the orbital surface of the maxilla, 

 immediately lateral to the opening of the naso-lacrimal duct. 

 It passes laterally, below the inferior rectus muscle, and, 

 inclining slightly posteriorly, ends in a thin membranous 

 tendon, which gains insertion into the lateral aspect of the 

 sclera of the eyeball under cover of the rectus lateralis. The 

 insertion is not far from that of the superior oblique, but 



