622 



MANUAL OF HISTOLOGY. 



is to say, towards the ciliary processes, this tough muscular plate breaks up 

 into a long, fan-shaped, wide-meshed network of thin bands (I), in which, 

 at last, the direction of the fasciculi changes gradually from being meri- 

 dional externally to equatorial in its inner portions, forming so the circular 



Fig. 580. Section through the ciliary region of the human eye (after Iwanoff). a, radi- 

 ating bundles of the ciliary muscle; 6, deeper bundles; c, circular network; d, annular 

 bands of Mutter; e. tendon of ciliary muscle; /, muscles on the posterior side of the iris; 

 g, muscles on the ciliary border of same ; A, ligamentum pectinatum. 



network. Finally, internally (d) the so-called " ring muscle" of Muller 

 makes its appearance. This is formed of tolerably strong fascicles, the 

 anterior quite independent, the posterior taking their rise from the mus- 

 cular structure just mentioned. 



This, then, is the arrangement of the ciliary muscle of man, but among 

 the other mammalia it is thoroughly retiform (Flemming). It is strongest 

 amongst the beasts of prey, weaker among ruminants, and especially so 

 in the rodents. Although there still exists much difference of opinion 

 in regard to many minor points relating to the functions of this muscle, 

 it is commonly agreed that it plays an important part in the accom- 

 modation of the eye. 



In the iris or diaphragm the connective-tissue cells of the whole uvea 

 present themselves again. In blue eyes, however, they are devoid of pig- 

 ment, while in those of other deeper tints they are more or less crowded 



with either lighter or darker 

 yellowish, brownish, or even 

 black granules. Between 

 these cells the ground sub- 

 stance is no longer homo- 

 geneous, but streaky and 

 broken up into fibrillse, in 

 fact, it has become genuine 

 fibrous connective-tissue. 



The muscular character 

 of the iris has been long 

 recognised. In the first 

 place, we encounter around 

 the central aperture, but 

 more towards its posterior aspect, a muscle known as the sphincter pupiU<& 

 This is composed of a system of circular bundles of smooth muscular 

 tissue, of about-0-8-1 mm. in breadth in man (fig. 581, a). From this 

 sphincter other separate bundles of contractile fibre cells take their rise (as 



Fig. 581. Surface view of the human iris (after Iwanoff"). or, 

 the sphincter; 6, dilator of the pupil. 



