THE NERVOUS SYSTEM 



247 



the very small mucus-secreting gland at the medial canthus. 

 It is usually vestigial or absent in man and other primates. 

 The muscles controlling the movements of the eyeball are 

 seven in number: four are recti muscles, two are oblique, and 

 one is a retractor. The recti muscles (Fig. 104) originate on 

 the bone around the optic foramen, and are inserted on the 

 sclerotic coat, caudad of the equatorial ring. The external 

 rectus is inserted on the lateral aspect; the internal rectus, on 

 the medial aspect; the superior rectus, on the dorsal aspect; 

 and the inferior rectus on the ventral aspect. The superior 



Fig. 119. — Longitudinal Section of the Eye. 

 aq. Aqueous humor; c, cornea; cp, capsule of the lens; ch, choroid; ci, ciliary 

 process; i, iris; Ig, ligament of lens; m, ciliary muscle; opn, optic nerve; rt, retina; 

 sc, sclerotic coat; os, ora serrata. 



oblique muscle arises from the sphenoid bone medial of the 

 optic foramen, extends along the medial wall of the orbital 

 cavity to its dorso-medial margin, where it passes through a 

 tendinous loop fastened to the frontal bone and then turns 

 laterad to its insertion in the sclerotic beneath the superior 

 rectus. The inferior oblique arises from the lachrymal bone 

 and is inserted on the sclerotic between the external and in- 

 ferior recti muscles. The above muscles may be demonstrated 



