SECTION IX 

 MOVEMENTS OF THE EYEBALLS 



IN order to obtain distinct vision of any object, an image of 

 it must be formed on the fovea centralis. Visual attention, i.e. 

 the fixing of the gaze on any object, involves the adjustment of the 

 visual axes by movements of the eyeball, in order that the image of the 

 object of attention shall fall on the central spot in each eye. 



The eyeball rests on a pad of fat surrounded by a denser capsule 

 of connective tissue, the capsule of Tenon, from which it is separated 

 by a lymph space. Within this space it is able to rotate around axes 

 which pass through a point almost in the middle of the eyeball. These 

 movements of rotation are carried out by the six ocular muscles, the 

 four recti and the two oblique. The four recti muscles the superior, 

 inferior, external, and internal arise from a continuous tendinous oval 

 ring which is attached at the back of the orbit to the margin of the optic 

 foramen and sphenoidal fissure. From this common origin the muscles 

 pass forwards as flat bands close to the walls of the orbit ; they come 

 in contact with the eyeball at its equator, passing through the sur- 

 rounding lymph space, and are attached to the eyeball about 7 mm. 

 behind the margin of the cornea, their positions being indicated by 

 their names. Of these muscles the internal rectus is the thickest and 

 strongest ; the superior rectus is the thinnest and weakest. 



The superior oblique muscle arises in a short tendon attached 

 to the back part of the orbit in front of and internal to the optic fora- 

 men. The muscle runs forwards in the upper and inner angle of the 

 orbit and ends in a round tendon, which passes through a fibrous 

 pulley at the upper and inner angle behind the anterior margin of the 

 orbit. The tendon then makes a sharp bend and passes outwards, 

 backwards, and downwards between the superior rectus muscle and 

 the eyeball, and is attached to the latter just below the outer edge 

 of the superior rectus, behind the attachments of the rectus muscles 

 and about half-way between the anterior and posterior poles of the 

 eyeball. 



The inferior oblique muscle rises from the orbital plate of the 

 superior maxilla, just within the anterior margin of the orbit. The 

 muscle forms a flat band and passes upwards, backwards, and out- 

 wards between the superior rectus and the wall of the orbit, and ends 



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