THE HEAD, ANTERIOR. 53 



Insertion. The two recti are inserted into the sclerotic 

 of the eye-ball about a fourth of an inch behind the corneo- 

 sclerotic junction. 



Nerve Supply. The external rectus by the sixth cranial 

 nerve, the other by the third. 



Action. The external and internal recti muscles move 

 the eye-ball outward or inward without any rotation. 



The Ophthalmic Artery and Branches. 



The ophthalmic is a large branch from the front of the 

 internal carotid as it is turning upward to the brain through 

 the cavernous sinus. 



The artery enters the orbit through the optic foramen, 

 with the optic nerve lying external and inferior to the 

 nerve. 



The artery runs forward in a tortuous course above the 

 optic nerve and along the inner side of the orbit to the 

 front of the same, where it divides into the nasal and frontal 

 branches. 



Its branches are the lachrymal, to the lachrymal gland ; 

 the supra-orbital, which accompanies the nerve of the same 

 name through the supra-orbital notch or foramen to the 

 front of the forehead (see page 26) ; the central artery of 

 the retina, which penetrates the optic nerve one-fourth of 

 an inch behind the eye-ball and runs within that nerve to 

 the retina ; the muscular, to the muscles of the eye ; the 

 ciliary arteries, grouped in three sets, the short posterior 

 (five or six), the long posterior (two), and the anterior 

 ciliary, from the surrounding muscular branches and lach- 

 rymal artery ; all these pass to the eye, the posterior to its 

 fundus and the anterior along the tendons of the muscles 

 to the middle zone of the eye ; the posterior ethmoidal, 

 which leaves the orbit through the posterior ethmoidal 



