1036 



ORGANS OF SPECIAL SENSE 



fossa just named. On passing through this pulley, or trochlea, the tendon bends 

 at an angle of 50, running backwards and outwards under thesuperior rectus to 

 its insertion into the sclerotic. It is supplied by the fourth nerve. 



The inferior oblique arises from the front of the orbit, about the junction of its 

 inner and lower walls, just external to the lower end of the lachrymal groove. It 

 runs, in a sloping direction, outwards and backwards, lying at first between the 

 inferior rectus and the orbital floor, then between the external rectus and the globe; 



FIG. 734. DIAGRAMMATIC REPRESENTATION OK ORIGINS OF OCULAR MUSCLES AT THE APEX 



OF THE RIGHT ORBIT. 

 (After Schwalbe, slightly altered.) 



Superior reetus 



FOURTH NERVE 



f -x 

 Lncliri/nirtl and frontal f-i>t \ ^. {. 



Origin of external rectus from fibrous bridge ^^^^y" 



over superior orbital fissure [ 



Sfaso-ciliary of JiJ'tti n< : r 



SIXTH NER VE 



Levator palpebrae superioris 



JL 



~^L ^ Superior oblique 



Q V_ Ill'l ir 1-OHA.M1CX AXD XERVE 

 '-> Internal rectus 



Inferior rectus 

 External reetus Till 11 1> -\7,7.' I A' 



finally it ascends slightly, to be inserted by a short tendon into the sclerotic at the 

 back of the eye. Its nervous supply is derived from the third nerve. The precise 

 manner of insertion of the different ocular muscles has been described above in our 

 EXAMINATION OF THE EYEBALL. (For MUSCLES OF THE EYELIDS AND EYEBROWS, 

 see pages 331 and following.) 



Action of the ocular muscles. While rotating the globe so that the cornea is 

 turned in different directions, the ocular muscles do not alter the position of the 

 eyeball in the orbit either laterally, vertically, or antero-posteriorly. In speaking, 



FIG. 735. THE MUSCLES OF THE EYE SEEN H:OM THE TEMPORAL SIDE. 



(After Testut.) 



Levator palpebrae 

 superioris 



Superior rectu 

 Internal rectua 



OPTIC NERVE 



External rectus, cut, / 

 showing double lig- 

 ament to bone 



Inferior rectus 



Frontal sinus 



SUPRA ORBITAL 

 XI-: R VE 



Superior oblique 



External rectus, cut 



Inferior oblique 



Maxillary sinus 



therefore, of the eye being moved upwards or outwards, etc., it is the altered position 

 of the cornea or front of the eye that we mean to express; it is manifest that, if the 

 cornea moves up, the back of the eyeball must simultaneously be depressed, and 

 similarly with other movements. All the movements of the globe take place by rota- 

 tion, on axes passing through the centre. Though the possible axes are numerous 

 in combined muscular action, there are three principal axes of rotation of the eye- 

 ball, and in reference to these the action of individual muscles must be described. 



