I\L\MMALS 



479 



may penetrate as far as the nuclei of the rods and cones. ^ Leber 

 (1903) divided the retinae of Placentals in this respect into 4 groups : — 

 {a) HOLANGiOTic (oAo?, all ; dyyelov, vessel) (Plates XIV, XV ; 

 Figs. 631-2). The whole retina receives a direct blood supply either 

 from a central artery or from cilio -retinal arteries which emerge either 

 as a single trunk or as several branches from or around the optic disc. 

 This type of vascularization occurs in some Insectivores (the hedgehog, 

 Erinaceus. tlie mole. Talpa). some Rodents (mouse, squirrel, marmot). 



Fig. bo.J 



The Fundus of the Squirrel, Scjcju': 

 (Lindsay Johnson). 



some Carnivores (Felidse, Canidse, Ursidse, some Viverridse and the 

 Pinnipedia), in a few Ungulates (pig. ox), and the Primates. - 



In Primates the central artery emerges from the disc as a single vessel, 

 but more usually several large arteries emanate therefrom ; in Carnivores 

 a number of small arteries of the ciliary type emerge from the margin of the 

 disc. In the squirrel and the marmot the disc is a long horizontal line from the 

 entire length of which the vessels emerge (Fig. 635). 



(b) MERAXGiOTic (jnepo?, jDart) (Fig. 633). Part of the retina is 

 supplied with vessels. This is only seen in the Lagomorpha (rabbit 

 and hare), in ^hich the vessels are limited to the horizontal expansions 

 of medullated nerve fibres (Figs. 633, 637). 



1 For literature, see particularly H. Muller (1861). Sattler (1876), Leuckart (1876), 

 His (1880), Brims (1882), Barrett (1886), Schuitze (1892), Johnson (1901), Leber (1903), 

 Darnel and Fortin (1937) (bat), Michaelson (1948-54), Rohen (1954) (rabbit). 



^ Comijare also the Marsupials, Didelphys and Petaurus, p. 440. 



