3 68 



HISTOLOGY. 



smooth muscle fibers about 3 mm. broad and 0.8 mm. thick anteriorly; 

 it arises beneath the sinus venosus of the sclera and tapers toward the ora 

 serrata (Fig. 410). It consists of two sets of fibers, the meridional and 



circular. The meridional fibers 

 as seen in section (p. 356), 

 form a triangular group con- 

 verging toward the sinus veno- 

 sus. Their numerous outer- 

 most bundles mixed with elas- 

 tic tissue are applied to the 

 s c 1 e r a 1 surface. Anteriorly 

 the bundles become gradually 

 shorter and more radially 

 placed so that those in the 

 front of the muscle are perpen- 

 dicular to the sclera. The 

 radial fibers are classed as a 

 separate group by Professor 

 Stohr. The circular fibers 

 which vary in number in different individuals form that part of the 

 ciliary muscle which is nearest to the equator of the lens. 



The iris consists of its stroma anteriorly and the pars iridica retinae 



FIG. 420. A, FROM A TEASED PREPARATION OF A HU- 

 MAN CHORIOID. X 240. p, Pigment cells; e, elastic 

 fibers; k, nucleus of a flat non-pigmented cell; the 

 cell body is invisible. 



B, PORTION OF A HUMAN CHORIOCAPILLARIS AND THE 

 ADHERENT LAMINA BASALIS. X 240. c, Wide 

 capillaries, some of which contain (b) blood cor- 

 puscles; e, lamina basalis, showing a fine "lattice 

 work." 



Mesenchymal 

 epithelium. 



Loose connective 

 tissue. 



Vascular layer. 



Spindle cell layer. 



Pars iridica 

 retinae. 



FIG. 421. VERTICAL SECTION OF THE PUPILLARY PORTION OF A HUMAN IRIS. X 100. About one- 

 fifth of the entire width of the iris is shown. 



g, Blood vessel, with thick connective tissue sheath ; m, sphincter pupillae muscle cut transversely ; p, 



pupillary border of the iris. 



posteriorly, and is covered by the mesenchymal epithelium of the chambers 

 of the eye. The anterior epithelium is a simple layer of flat polygonal 

 cells [unfortunately named endothelium]. The stroma consists anteriorly 



