130 SPECIAL SENSES. 



posterior two-thirds of the globe, and is loosely attached to 

 the sclerotic. It is perforated by the optic nerve posteriorly, 

 and by the tendons of the recti and oblique muscles of the 

 eyeball in front, being reflected over these muscles. It is 

 also continuous with the palpebral ligaments and is attached 

 by two tendinous bands to the border of the orbit at the in- 

 ternal and the external angles of the lids. 



The muscles which move the globe are six in number for 

 each eye. These are, the external and internal recti, the su- 

 perior and inferior recti, and the two oblique muscles. The 

 four recti muscles and the superior oblique arise posteriorly 

 from the apex of the orbit. The recti pass directly forward 

 by the sides of the globe and are inserted by short, tendinous 

 bands into the sclerotic, at a distance of from one-fourth to 

 one-third of an inch from the margin of the cornea. The 

 superior oblique, or trochlearis muscle passes along the upper 

 and inner wall of the orbit to a point near the inner angle. 

 It here presents a rounded tendon, which passes through a 

 ring, or pulley of fibro-cartilage ; and it is from this point 

 that its action is exerted upon the globe. From the pulley, 

 or trochlea, the tendon becomes flattened, passes outward and 

 backward beneath the superior rectus, and is inserted into 

 the sclerotic, about midway between the superior and the ex- 

 ternal rectus and just behind the equator of the globe. The 

 inferior oblique muscle arises just within the anterior margin 

 of the orbit, near the inner angle of the eye, and passes 

 around the anterior portion of the globe, beneath the inferior 

 rectus and between the external rectus and the eyeball, tak- 

 ing a direction outward and slightly backward. Its tendon is 

 inserted into the sclerotic, a. little below the insertion of the 

 superior oblique. The general arrangement of these muscles 

 is shown in Fig. 8. 



The various movements of the eyeball are easily under- 

 stood by a study of the associated movements of the muscles 

 just enumerated, at least, as far as is necessary to the compre- 

 hension of the mechanism by which the eyes are directed 



