596 AMPHIBIANS 



behind the limbus. The posterior side of the triangle is faced with the 

 usual two-layered ciliary epithelium, and distally bears nearly a hundred 

 low folds, which continue meridionally onto the back of the iris. In 

 Rana, these iris folds run nearly to the pupil; but in Bufo they go only 

 half-way, and are lacking mid-dorsally and mid-ventrally (except for the 

 two 'ciliary processes'). From the posterior, plicate face of the ciliary 

 body, discrete cuticular fibers fan out to constitute a zonule; but these 

 are embedded in vitreous, which fills what would otherwise be the pos- 

 terior chamber. Mid-ventrally, a single prominent fold — large enough 

 to be called a 'ciliary process' — runs from the ora terminalis to the pupil 

 and there terminates in the ventral pupillary nodule (Fig. 172). Mid- 

 dorsally, two or three large folds are approximated, and aligned with a 

 dorsal pupillary nodule (possessed by most anurans in addition to the 

 ventral one; exception: Rana temporaria) . The zonule fibers stemming 

 from these heaviest uveal folds are the most important for the suspen- 

 sion of the lens, and transmit the force which protracts it in the act of 

 accommodation. 



The anterior face of the ciliary triangle, bounding the anterior cham- 

 ber peripherally, runs from the limbus (or, dorsally and ventrally, from 

 the sclera behind the limbus) to the root of the iris, and is supposedly 

 covered by a continuation of Descemet's mesothelium (which, however, 

 if present at all, is in the form of a discontinuous patchwork). The 

 central area of the triangle is filled by a meshwork of vascular and pig- 

 mented connective tissue', forming a pectinate ligament of a sort. At the 

 base of the triangle, against the sclera, lie two structures which can best 

 be seen in vertical sagittal sections of the eye : the ciliary muscle, and 

 the canal of Schlemm. Neither of these forms a complete annulus around 

 the anterior segment as in higher vertebrates, but both the muscle and 

 the canal take the form of a dorsal-ventral pair of crescents, with gaps 

 between their horns nasally and temporally. Each canal has connections 

 with iris veins and, through the sclera, with conjunctival veins and 

 arteries. Their comparability with the Schlemm's canals of higher verte- 

 brates is most dubious; and even their function is in doubt, since they are 

 often widely separated from the anterior chamber and the aqueous which 

 they might be presumed to drain from the eyeball. Equally puzzling are 

 the dorsal and ventral ciliary muscles. These contain meridional fibers, 

 in some species circular ones as well. The meridional fibers run along the 

 inner surface of the sclera to insert in the chorioid; but it is difficult to 

 see, considering their location, what these muscles can accomplish. They 



