718 



SPECIAL SENSES. 



In experiments analogous to those just described, made with strongly 

 colored objects, it has been observed that the border of irradiation takes a 

 color complementary to that of the object itself. This is particularly well 

 marked when the objects are steadily looked at for some time. Illustrations 

 of this point also are very simple. In looking steadily at a red spot or figure 

 on a white ground, a faint areola of a pale-green soon appears surrounding 

 the red object ; or if the image be yellow, the areola will appear pale-blue. 

 These appearances have been called accidental areolae. 



MOVEMENTS OF THE EYEBALL. 



The eyeball nearly fills the cavity of the orbit, resting, by its posterior por- 

 tion, upon a bed of adipose tissue, which is never absent, even in extreme 

 emaciation. Outside of the sclerotic, is a fibrous membrane, the tunica vag- 

 inalis oculi, or capsule of Tenon, which is useful in maintaining the equilib- 

 rium of the globe. This fibrous membrane surrounds the 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 tendin- 

 ous bands, to the border of the orbit, at the internal 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 superior and inferior recti and the 



10 



FIG. 259. Muscles of the eyeball (Sappey). 



1 attachment of the tendon connected with the inferior rectus. internal rectus and external rectus ; 2, 

 external rectus, divided and turned downward, to expose the inferior rectus ; 3, internal rectus ; 4, 

 inferior rectus ; 5, superior rectus ; 6, superior oblique ; 7, pulley and reflected portion of the supe- 

 rior oblique : 8, inferior oblique ; 9, levator palpebri superioris ; 10, 10, middle portion of the levator 

 palpebri superioris ; 11, optic nerve. 



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 



