THE AXIAL MUSCLES. 



503 



2. Rectus Superior (Fig. 514). 



Attachments. — The superior rectus arises from the upper portion of a fibrous 

 ring termed the annulus of Zin^i (annuhis tendineus communis), which surrounds the 

 optic foramen and is formed by a thickening of the orbital periosteum in that region. 

 Thence the muscle is directed forward over the eyeball and is iyiserted into the 

 sclera a little above the upper margin of the cornea. 



Nerve-Supply. — From the oculo-motor nerve. 



Action, — To rotate the eyeball so that the pupil is directed upward and at the 

 same time somewhat inward. 



3. Rectus Internus (Fig. 514). 



Attachments. — The internal rectus (m. rectus medialis) arises from the inner 

 portion of the annulus tendineus communis and passes forward along the inner wall 

 of the orbit to be inserted into the sclera a short distance behind the inner margin of 

 the cornea. 



Nerve-Supply. — From the oculo-motor nerve. 



Action. — To rotate the eyeball so that the pupil is directed inward. 



Fig. 515. 



Superior rectus 



Levator palpebras superioris 

 Superior oblique 



Sphenoidal fissure 

 External rectus. J 



Optic nerve (cut 



Spheno-maxillary fissun 



Inferior oblique. 



Trochlea, tendon of superior 

 oblique in place 



.Internal rectus 



Inferior rectus 



Right orbit seen from before, showing stumps of ocular muscles attached to common tendinous ring of origin. 



4. Rectus Inferior (Fig. 516). 



Attachments. — The inferior rectus arises from the lower portion of the com- 

 mon tendinous ring, its line of origin being continuous with that of the rectus internus. 

 It is inserted into the sclera a short distance below the inferior margin of the cornea. 



Nerve-Supply. — From the oculo-motor nerve. 



Action. — To rotate the eyeball so that the pupil is directed downward and at 

 the same time somewhat outward. 



5. Rectus Externus (Fig. 514). 



Attachments. — The external rectus (m. rectus lateralis) arises by two heads, 

 one of which is attached to the lower and outer portion of the common tendinous ring 

 and to the spine on the lower border of the sphenoidal fissure, and the other to the 

 upper and outer part of the common tendinous ring. It passes along the outer wall 

 of the orbit and is inserted into the sclera a little behind the outer border of the cornea. 



Nerve-Supply. — From the abducens or sixth nerve. 



Action. — ^To rotate the eyeball so that the pupil is directed outward. 



Relations. — Between the two heads of the external rectus there pass the oculo- 

 motor, nasal, and abducent nerves and the ophthalmic vein. 



