1070 



SPECIAL SENSE ORGANS 



place by rotation, 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 eyeball, and in 

 reference to these the action of individual muscles must be described. Two of these axes are 

 horizontal and one vertical; they all pass through the centre of rotation at right angles to one 

 another. By rotation of the eye on its vertical axis the cornea is moved laterally (toward the 

 temple) and medially (toward the nose) : movements called respectively abduction and adduc- 



FiG. 813. — Dissection of the Muscles of the Right Orbit, Lateral View. 



Frontal sinus 



N. frontalis 



Frontal sinus \ 



Superior oblique 



Levator palpebrje superioris 

 Rectus superior 



Rectus medialis 

 Optic nerve \ 

 Annulus tendineus com- > 

 munis (Zinni) \ 



Lesser wing of sphenoid \ \ 



Sheath of optic nerve 



Rectus inferior 



Lateral rectus 

 Inferior oblique 



tion. In upward and downward movements of the cornea the eye rotates on its horizontal 

 equatorial axis. The other principal axis of rotation is the sagittal, which we have previously 

 described as corresponding to the line joining the anterior and posterior poles of the globe 

 (page 1055). In rotation of the eye on its sagittal axis, therefore, the cornea may be said to 

 move as a wheel on its axle, for its centre now corresponds to one end of the axis; in other words, 

 this is a rotation of the cornea. Such movements may, consequently, be expressed with refer- 

 ence to their effect on an imaginary spoke of the corneal wheel — e. g., one running vertically 



Fig. 814. — Dissection op the Muscles of the Left Orbit, From Above. 



Lateral rectus 

 Inferior oblique | 

 I 



Rectus medialis 



Rectus superior 

 , Tendon of superior oblique ' 

 , ; Trochlea of superior oblique 



^ ; Levator palpebrse superioris 



Levator palpebrse superioris 

 Periorbita 



upward from the corneal centre. Tliu.s we may say 'rotation of the corncji, laterally' when this 

 I)art of the wheel moves toward the lateral angle, or 'medially' when toward the nose. 



The only two muscl(>s that rotate; the eyciljall merely on one axis are tiie lateral rectus and 

 the medial rectus; the foriiKir abductitig, and tin; latter adducting, the cornea. The action of 

 the superior and inferior recti is complicated by the obliquitj' of the axes of muscles and globe 

 previously mentioned. 



