THE HEAD AND NECK 1 151 



of the cavity and the external rectus. The borders of the muscle 

 are anterior and posterior, the latter, as stated, receiving the nerve- 

 supply. 



Movements of the Eyeball. — ^The movements of the eyeball con- 

 sist of rotation round a point situated just behind the centre of its 

 antero-posterior axis. When the eyeball rotates round its vertical 

 axis horizontal or lateral movements take place, and the cornea 

 is directed outwards or inwards according to the muscle which acts. 

 The external rectus abducts the eyeball, so as to direct the cornea 

 outwards, and the internal rectus adducts the eyeball, so as to 

 direct the cornea inwards. When the eyeball rotates round its 

 transverse axis vertical or upward and downward movements take 

 place, and the cornea is directed upwards or downwards according 

 to the muscle which acts. The superior rectus elevates the eyeball, 

 and the inferior rectus depresses it. It is to be borne in mind, 

 however, that these two muscles in passing forwards have each a 

 slight inclination outwards. Whilst, then, they respectively elevate 

 and depress the eyeball, each of them also imparts to it a certain 

 amoimt of inward movement, accompanied by slight rotation. 

 In the case of the superior rectus this inward and rotatory move- 

 ment is corrected by the inferior oblique acting in association with 

 it, and in the case of the inferior rectus by the superior oblique 

 acting in association with it. 



Direct elevation of the eyeball is therefore effected by the superior 

 rectus, aided by the inferior oblique, and direct depression of the 

 eyeball is effected by the inferior rectus, aided by the superior 

 oblique. The superior oblique, acting alone, depresses the eyeball, 

 and abducts it, or turns it outwards, and the inferior oblique, 

 acting alone, elevates the eyeball, and abducts it, these movements 

 in each case being accompanied by slight rotation. 



Fascia of the Orbit. — ^This fascia forms (i) the capsule of Tenon, 

 and (2) sheaths for the ocular muscles. 



The capsule of Tenon forms a connective-tissue covering for the 

 sclerotic coat of the eyeball, and extends from the point of entrance 

 of the optic nerve to near the margin of the cornea. Posteriorly 

 it is perforated by the ciliary vessels and nerves, and blends with 

 the dura matral sheath of the optic nerve, and anteriorly it passes 

 beneath the ocular conjunctiva, with which it unites near the 

 margin of the cornea. The outer surface of the capsule is in con- 

 tact with the orbital fat, and anteriorly with the ocular conjunctiva. 

 The inner surface, which is smooth, is separated from the sclerotic 

 by a narrow space, which is crossed by delicate trabeculas of 

 connective tissue. This interspace is called the perisclerotic space, 

 or Tenon's space, and is regarded as a lymph space. The capsule 

 of Tenon forms a cavity or socket, within which the eyeball 

 glides with perfect freedom from friction. 



The lower part of the capsule of Tenon presents a thickening, 

 which is known as the suspensory ligament of the eye (Lockwood). 

 It is attached externally to the malar bone, and internally to the 



