342 MANUAL OF HISTOLOGY. 



In very hypermetropic eyes, on the contrary, the circular 

 fibres are abundantly developed (Fig. 155), the meridional fibres 

 are shorter, while the angle at the point of origin of the mus- 

 cle becomes somewhat obtuse, so that by these changes one can 

 determine, even in a microscopic section, what considerable 

 refractive error the eyes have had. 



The meridional fibres are either prolonged some distance 

 into the stroma of the ch'oroid and end in a delicate fringe, or 

 they terminate at the anterior and outer layers of this mem- 

 brane in stellate knots with fine anastomosing branches. 



The radial fibres form a looser network than the last, but 

 also have the same terminal interlacement of their fibres ; the 

 circular fibres form fewer anastomoses, and only those bundles 

 which lie next to the radial fibres are extensively connected 

 with them. 



The nerves of the ciliary body are derived from the plexus 

 formed in its stroma by the ciliary nerves ; the vessels are 

 largely supplied from the circulus iridis major, lying in the an- 

 terior part of the body. 



The iris arises from the anterior side of the ciliary body, 

 and from the connective tissue surrounding the fibres of the 

 ciliary muscle ; it is also attached to the cornea and sclera by 

 the ligamentum pectinatum. (See Fig. 153). 



It consists of a loose connective-tissue stroma, which sup- 

 ports a rich vascular network, a complete muscular structure, 

 and the nerves. It is covered anteriorly by a continuation of the 

 endothelium of the cornea, and posteriorly by a thick layer of 

 pigment-cells continuous with those which line the ciliary body. 

 The vessels arise from the circulus, have adventitial coats which 

 are thick in proportion to their calibre, and pass radially to 

 the margin of the pupil, where they form a network of fine 

 capillaries, the circulus arteriosus iridis minor, ending final- 

 ly in veins which return in the same general direction as the 

 arteries, but lie beneath them, emptying finally into the venae 

 vorticosae. 



Near the margin of the pupil, and forming a ring about 

 it 1 mm. in breadth by -^ mm. in thickness, is the sphincter 

 muscle of the iris. It is composed of unstriped muscular tissue, 

 and is situated in the posterior portion of the iris. 



The dilator muscle, at its inner border, is in close connection 

 with the sphincter, and its fibres run radially to the periphery 



