THE EYE 207 



latter by the trochlear nerve. The Lateral Rectus, supplied by 

 the abducent nerve, and the Medial Rectus, supplied by the 

 oculo-motor, produce lateral and medial rotation of the eyeball. 

 Motor Nerves of the Orbit. The Oculo-motor (third cerebral) 

 nerve supplies all the orbital muscles except the superior oblique 

 and the lateral rectus. In addition it gives off the short (motor) 

 root of the ciliary (lenticular) ganglion, and in this way supplies 

 the ciliary muscle and the sphincter pupillse. In complete 

 paralysis of the oculo-motor nerve, the pupil is widely dilated 

 by the dilatator pupillse (supplied by the sympathetic) and 



Supra-orbital nerve 

 Levator palpebrae superioris | Ophthalmic vein 



Roof of orbit ; ; 



Superior rectus ' i i Supra-trochlear nerve 

 Trochlear nerve 

 ; Superior oblique 



Naso-ciliary nerve 



Lacrimal n^^J^^^fUS^Sf <ifck>< - Ophthalmic artery 



Abducent nerve 



Oculo-motor nerve, Jf^\ 

 lower division 



Middle concha 

 - Maxillary sinus 



Infra-orbital nerve | Ophthalmic vein 

 Inferior rectus 



FIG. 63. Frontal Section through the Orbit, to show the relative 

 positions of the Muscles, Vessels and Nerves. 



does not react to light. The power of accommodation to dis- 

 tance is lost, and ptosis is present. Owing to the unopposed 

 action of the lateral rectus, which is not involved, a divergent 

 strabismus results, and the patient carries his head rotated to 

 the opposite side in order to compensate for his disability. 



The Trochlear (Fourth Cerebral) Nerve supplies the superior 

 oblique only. Paralysis of this nerve produces diplopia, when 

 the patient looks downwards, because, while pure downward 

 rotation is possible in the sound eye, the inferior rectus imparts 

 a medial as well as a downward direction to the eye on the affected 

 side, and the superior oblique, which should counteract the 

 medial rotation, is paralysed. 



The Abducent (Sixth Cerebral) Nerve supplies the lateral rectus 



