AMPHIBIANS 



347 



fibrous sclera without cartilage (except for anterior cartilaginous plaques 

 in Triton, and the small fragmented cartilage in Hynohius — Stadtmiiller, 

 1914-29 ; Tsusaki, 1925 ; Inagaki, 1930 ; Yatabe, 1931), the com- 

 paratively large size of the lens as would be expected in creatures 

 favouring dimly-lit surroundings, the comparatively shallow anterior 

 chamber, the thicker and less highly organized choroid separated from 

 the sclera by large serous spaces, the lack of ciliary folds on the inner 

 surface of the ciliary body and iris with the exception of a single mid- 

 ventral ciliary process, the lack of a dorsal protractor lentis muscle in 

 the place of which the suspensory ligament is strengthened locally as in 

 Fishes, the lack of pupillary nodules, of the primitive and discontinuous 

 ciliary venous sinuses, and of an area centralis in the retina. Accom- 

 modation is thus effected through a ventral protractor lentis muscle after 

 the manner seen in selachian fishes, by a forward pendular movement 

 of the lens rather than its forward displacement as a whole (Beer, 1898). 



The vascular supply to the anterior segment is similar in its general 

 plan to that of the Anurans, but curiously the vascular arrangements 

 in the iris partake of a more definite pattern (Plate IV) ; as in the frog, 

 the arteries are superficial but instead of entering at various apparently 

 haphazard positions around the circumference as in this animal, they 

 are represented in the salamander by two trunks, an inferior and a 

 temporal artery of the iris, an arrangement anticipating that seen 

 typically in Reptiles such as the lizard (Plate V) (Mann, 1929). 

 Sometimes the inferior artery of the iris is a branch of the temporal 

 and does not enter separately. The arteries break up irregularly round 

 the pupil and the blood is drained away by a few radial veins lying 

 in a deeper plane so that they are often obscured by pigment. In 

 newts {Triturus, Pleurodeles) the artery breaks up into some 6 branches 

 which encircle the pupil and drain aA\'ay on the nasal side (Mann, 1931). 



In tailed Amphibians the pupil is usuall}^ round and the iris may 

 be brilliantly pigmented — dark brown with faint metallic flecks in the 

 spotted salamander {Salamandra maculosa), horizontal green and brown 

 banding in the Californian newt {Triturus torosus), sage-green with 

 peripheral horizontal bands of metallic gold in the Japanese newt 

 {Trititriis 2)l/rrhogaster), and so on (Mami. 1931) (Plate IV, Fig. 1). 



The fundus in salamanders is uniformly the same throughout, of 

 a pinkish hue with a granular texture in the middle of which the 

 circular grey optic disc is set (Plate IV, Fig. 2). The retina is 

 avascular and there is no membrana vasculosa retinae as in Anurans 

 (Virchow, 1881) {Salamandra, H\Ttl, 1861 ; Triton, Kessler, 1877). 



The visual elements tend to be sparser and larger than in the frog, 

 but are generally of the same morphological types except for the 

 absence of oil-droplets in the cones (Fig, 413-5), and the occasional 

 lack of green rods (in Salamandra). 



Trit 



urus cristatus 

 (male) 



Trit 



urus cristatus 

 (female) 



