THE EYE. 413 



The muscle-fibres are long-, spindle-cells, which are abruptly 

 swollen in the middle, where the miclei are situated ; the nucleus is 

 oval, O'OOQ crooi2 mm. in length, 0^0025 mm. broad, and occupies 

 nearly the whole of the swollen part of the cell (Hoffmann, 

 Griinbagen). 



According to Koganei the iris possesses a M. constrictor irid'is (L c. 

 Berlin Sitzungsber.), but no 31. dilatator iriflis ; in a former publica- 

 tion (7. c. Arch. mik. Anal.) he was unable to find any muscular 

 fibre, and holds the muscle-fibres of Griinhagen to be connective- 

 tissue elements. 



The stroma consists of delicate connective-tissue fibrils, enclosing- 

 a very large number of pigmented, branched cells. 



a. The arteries of the iris (Fig. 256 II) arise from an arch (see 

 Vessels of Eye) formed by the A. ophthalmica in the corpus ciliare. 

 It commences between the ventral and temporal surfaces by two 

 branches : one courses along the temporal border, the other along 

 the nasal, to meet each other on the nasal surface ; the former 

 courses through one-third, the latter embraces two-thirds of the 

 circumference at the iris. 



The temporal artery courses along the ciliary border during the 

 first third of its course, it then gradually approaches the border of 

 the pupil ; the nasal artery runs at once towards the pupil. On 

 the nasal border of the pupil they anastomose by their branches, 

 and so form a circulu* iridi-s major. 



Except near their termination, no small vessels arise from this 

 arterial circle ; in Fig. 256 II, for example, only five larger branches 

 are given off, three from the temporal side and two from the nasal. 

 The five large branches run towards the circumferential border of 

 the iris and break up into numerous vessels, which form a very 

 irregular and open network. From this network arise the vaaa 

 recta already described.. 



d. The lens is almost spherical, and is composed of cellular ele- 

 ments enclosed in a capsule (capsula lenti*). 



The capsule is a homogeneous, transparent, structureless, and 

 highly elastic membrane. The deeper surface of the anterior cap- 

 sule is lined with a simple layer of regular nucleated six-sided 

 epithelial cells. 



The lens itself consists of long, flat fibres ; seen from the surface 

 these are broad, narrow edge-wise, and in section six-sided prisms. 

 Those lying parallel to the anterior and posterior surfaces are 



