THE CILIARY APPARATUS AND THE IRIS 



667 



A radial layer of muscle, figure 445, is knitted into the base of the cornea, on 

 the one hand, and extends back into the choroid, on the other. Thick bun- 

 dles of the circular fibers are also present in this mass of muscle. From the 

 ciliary processes, extending over the lens, is the iris. It is a sheet of connec- 

 tive tissue and muscle lined with epithelium and highly pigmented. 



In the middle anterior portion is a round aperture, the pupil. The mus- 

 cle fibers are arranged circularly and radially and are of the unstriated 

 muscle type. Contractions of the circular muscles of the iris produce con- 



anterior ciliary arteries and vein 



greater arterial circle 

 angle of tbe IrU 



canal of schlemm 



ciliary muse!* 



limbus cornese. 



aaterior chamber 



epithelium 



anterior limiting ( 

 membrane f 



capsule ot leus 



posterior limiting membrane 



stroraa of iris 

 posterior surface of iris 

 spbiucter of. pupil 



FIG. 445. Meridional Section of a Portion of the Anterior Part of the Eyeball. (Toldt.) 



striction of the pupil, while contractions of the radial fibers produce dilata- 

 tion. Both the ciliary apparatus and the iris are supplied with motor nerves. 

 Fibers of the third cranial nerve are distributed to the ciliary muscles, 

 apparently to both radial and circular muscles, and when these nerves are 

 stimulating the resulting contractions of the muscles tend to remove the ten- 

 sion from the capsule of the lens. These nerve fibers pass through the ciliary 

 ganglion where they form a synapsis with ganglionic cells. Motor fibers 

 from the third cranial nerve also supply the circular muscles of the iris, which 

 produce constriction of the pupil through the motor nerves by way of the 



