THE THIRD OR MOTOR OCULI NERVE. 



795 



The superior division, the smaller, passes inward over the optic nerve, an;l 

 supplies the Superior rectus and Levator palpebrae. It occasionally communi- 

 cates with the ganglionic branch of the nasal nerve. 



The //(/'<//'// din'xitin, the Jarger, divides into three branches. One passes 

 beneath the optic nerve to the Internal rectus ; another, to the Inferior rectus ; 

 and the third, the largest of the three, passes forward between the Inferior and 



Infratrochlear 

 nerve. 



Motor root. 

 Sensory root. 



Recurrent filament 

 to dura mater. 



FIG. 479. Nerves of the orbit. Seen from sibove. 



External recti to the Inferior oblique. From this latter a short, thick branch is 

 given off to the lower part of the lenticular ganglion, which forms its inferior 

 root. It also gives off one or two filaments to the Inferior rectus. All these 

 branches enter the muscles on their ocular surface, except that to the Inferior 

 oblique, which enters its posterior border. 



Surgical Anatomy. Paralysis of the third nerve may be the result of many causes : as 

 cerebral disease; conditions causing pressure on the cavernous sinus; periostitis of the bones 

 entering into the formation of the sphenoidal fissure. It results, when complete, in (1) ptosis, 

 or drooping of the upper eyelid, in consequence of the Levator palpebrae being paralyzed ; (2) 

 external strabismus, on account of the unopposed action of the External rectus muscle, which 

 is not supplied by the third nerve, and is not therefore paralyzed ; (3) dilatation of the pupil, 

 because the sphincter fibres of the iris are paralyzed; (4) loss of power of accommodation, as 

 the sphincter pupillae, the ciliary muscle, and the Internal rectus are paralyzed ; (5) slight 

 prominence of the eyeball, from the compressing action of the Superior oblique, which is not 

 paralyzed. Occasionally paralysis may affect only a part of the nerve ; that is to say, there may 

 be, for example, a dilated and fixed pupil, with ptosis, but no other signs. Irritation of the 

 nerve causes spasm of one or other of the muscles supplied by it ; thus, there may be internal 

 strabismus from .spasm of the Internal rectus ; accommodation for near objects only from spasm 

 of the ciliary muscle, or myosis, contraction or the pupil, from irritation of the sphincter of (he 

 pupil. 



