1098 



THE ORGANS OF SPECIAL SENSE 



ANNULUS 

 ,C I LIAR IS 



RBICULUE 

 CILIARIS 



POSTERIOR 

 SMOOTH 

 PORTION 

 OF CHOROID 



INNER 

 SURFACE' 



OF SCLERA 



CORNEA (pos- 

 terior surface) 



FIG. 803. The middle or vascular coat of the eye- 

 ball exposed from without. Left eye, seen obliquely 

 from above and before. (Toldt.) 



806 and 820), the more numerous, arise at the point of junction of the cornea 

 and sclera, and partly also from the ligamentum pectinatum iridis, and, passing 

 backward, are attached to the choroid opposite to the ciliary processes. One 

 bundle, according to Waldeyer, is continued backward to be inserted into the 

 sclera. The circular fibres (fibrae circulares [Mulleri]) (Figs. 806 and 820) are 



internal to the radial ones and to some 

 extent unconnected with them, and 

 have a circular course around the at- 

 tachment of the iris. They are some- 

 times called the "ring muscle" of Miiller, 

 and were formerly described as the 

 ciliary ligament. They are well devel- 

 oped in hyperme tropic, but are rudi- 

 mentary or ajbsent in myopic eyes. The 

 Ciliary muscle is admitted to be TTie 

 chief agent in accommodation i. e., in 

 adjusting the eye to the vision of near 

 objects. When the Ciliary muscle 

 contracts, it draws the choroid for- 

 ward, and relaxes the suspensory 

 ligament. The elasticity of the lens at 

 once allows it to bulge forward until 

 it is again checked by the tension of the capsule; 1 the pupil is at the same time 

 slightly contracted. 



The Iris (iris, a rainbow) (Figs. 807 and 809) has received its name from its 

 various colors in different individuals. It is a thin, circular contractile curtain, 

 suspended in the aqueous humor between the cornea and the lens, being perfo- 

 rated a little to the nasal side of its centre by a circular aperture, the pupil (pupilld) 

 (Fig. 809), for the transmission 

 of light. The pupil of a living 

 person varies in size under the 

 influence of light and in efforts 

 at accommodation. In looking 

 at a near object the pupil is 

 small; in looking at a distant 

 object it is large. In light the 

 pupil contracts, in darkness it 

 dilates; hence the pupil is a 

 window which permits light to 

 pass into the interior of the 

 eye. The size of this window 

 depends on the contraction or 

 relaxation of the iris. The iris 

 divides the aqueous chamber (the 

 space between the cornea and 

 lens) into an anterior chamber and 

 a posterior chamber which com- 

 municate through the pupil (Fig. 



796). ^ By its circumference or ciliary margin (margo ciliaris} (Figs. 806 and 807) 

 the iris is continuous with the ciliary body, and it is also connected with the posterior 

 elastic lamina of the cornea by means of the pectinate ligament (ligamentum pectina- 

 tum iridis} (Fig. 820). The pectinate ligament of the iris is derived from the posterior 



FIG. 804. The arteries of the choroid and iris. The sclera 

 has been mostly removed. (Enlarged.) 



1 Stewart, Manual of Physiology. 



