MAMMALS 



449 



Fig. 562. — Diagram of the Eye of a Placental. 



Ch, choroid ; CM. ciliary muscle ; OX, optic nerve ; PL, pectinate 

 ligament bridging the ciliary cleft ; So, sclei-a ; Z, zonule. Xote the relative 

 simplicity of the eye. 



Fig. 563. — Section of the Eye of the Cat ( x 3-25) (Xorman Ashton). 



Tlie size of the globe varies within wide Hniits ; neglecting the 

 minute degenerate eyes of the mole (0-8 mm. diam.) and one or two 

 species of burrowing rodents/ it ranges from 1 to 2 mm. in diam. 

 in the shrews and bats to the enormous eyes of some whales (145 x 

 129 X 107 mm. in the great blue whale, BalcenojJtera musculus) (Putter, 

 1903). In comparison with the size of the body, however, that of the 

 eye is more uniform ; wliile the former varies as 1 : 60 among 

 terrestrial Placentals, the latter only varies as 1 : 30. The eye of 

 the seal (internal antero-posterior diam., 52 mm.) is comparatively 



1 p. 733. 



