THE ORBIT 



257 



the cavernous sinus can now be traced into the orbital cavity, 

 and 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 upper head of the lateral rectus muscle, on very 

 much the same plane (Fig. 96). The other nerves enter 

 between the heads of the lateral rectus the superior division 

 of the oculo-motor nerve occupying the highest place ; next 

 comes the naso-ciliary nerve ; then the inferior division of 

 the oculo-motor nerve ; and the abducent nerve is the lowest. 



Frontal nerve 



Superior rectus 

 M. levator palpebrse 



Lacrimal nerve 



Trochlear nerve 



Naso-ciliary j 

 nerve 



M. rectus 

 lateralis 



Abducens nerve 

 Inferior orbital fissure 



Superior division of 

 third nerve 



M. obliquus superior 



I [Optic foramen 



M. rectus inferior 



Inferior division of 

 oculo-motor nerve 



FIG. 96. Diagram of the Orbital Cavity, and of the origin of the ocular 

 muscles in relation to the optic foramen and the superior orbital fissure, 

 and the nerves that traverse the fissure. 



Insertions of the Muscles which move the Eyeball. The 

 recti are inserted into the sclera, 6 to 8 mm. (about quarter of 

 an inch) behind the cornea. The medial rectus has the 

 most anterior insertion, and both the medial and lateral recti 

 are attached a little further forwards than the superior and 

 inferior recti. The insertions of the superior and inferior 

 oblique muscles are both much further back than the inser- 

 tions of the recti, behind the transverse vertical plane which 

 divides the eyeball into equal anterior and posterior parts, 

 and mainly lateral to an antero-posterior vertical plane which 

 divides the eyeball into equal lateral and medial halves. 



VOL. in 17 



