THE RECTI MUSCLES. 



619 



The SIXTH NERVE (tig. 230, 2 ) lies below the other nerves, and Sixth nerve, 

 above the ophthalmic veins, in the interval between the heads of 

 the external rectus. In the orbit it first lies against, and then 

 penetrates the inner surface of the external rectus muscle. 



RECTI MUSCLES. The internal (fig. 230, D), inferior (c), and external straight 

 recto' (B) are placed with reference to the eyeball as their names eyebai?- 0f 

 express. They arise posteriorly from the circumference of the optic origin. 



FIG. 230. THIRD VIEW OF THE ORBIT (ILLUSTRATIONS OF DISSECTIONS). 

 Muscles : Nerves : 



A. Upper rectus and levator pal- 

 pebrse thrown back together. 



B. External rectus. 

 o. Inferior rectus. 

 D. Internal rectus. 



F. Superior oblique cut, showing 

 the insertion. 



H. Insertion of inferior oblique. 



1. Upper branch of the third. 



2. Sixth nerve. 



3. Branch of third to inferior 

 oblique. 



4. Branch of third to inferior 

 rectus. 



5. Branch of third to internal 

 rectus. 



foramen by a common attachment, which partly surrounds the optic 

 nerve. The external rectus differs from the others in having two External 

 heads : the upper one arises on the outer margin of the optic foramen nea( } s s | 

 and joins the superior rectus in the common origin : the lower and 

 larger head blends on the one side with the inferior rectus in the 

 common origin, and on the other side is attached to a bony point on 

 the lower border of the sphenoidal fissure near the inner end, while 

 some of its muscular fibres are also connected with a tendinous band 



