mam:\la.ls 



471 



Figs. 607 to 610. — The Pupils of Placenta ls. 



Fig. 607.— The Eye of a Poxy. 



Showing the tj'pically horizontally oval pupil of an Ungulate 

 (photograph by Michael Soley). 



Fig. 60S. — Primate. 



Fig. 609.— Cat. 



Fig. 610.— Horse. 



The round pupil is characteristic of diurnal and strictly nocturnal tyjDes. 

 The verticallj- oval pupil is characteristic of nocturnal types which bask in the 

 sun. The horizontally oval pupil is characteristic of Ungulates and several 

 other types (see text). 



In the round pupil the sphincter muscle (solid lines) and the dilatator 

 muscle (broken lines) are symmetrically arranged. In the vertically oval pupil 

 part of the sphincter muscle surrounds the pupil but criss-crossing fibres 

 extend above and below to the periphery of the iris. In the horizontally 

 oval pupil most of the sphincter fibres encircle the pupillary aperture but other 

 fibres are orientated radially on each side to be anchored in connective tissue 

 (shown stippled in Fig. 610) in the nasal and temporal parts of the iris ; 

 these areas are devoid of dilatator fibres (from drawings by Eversbusch and 

 Gordon Walls). 



depending not on diet l)ut on habit, an adaptation in the fir.st case to 

 suit diurnal, shade-loving animals, in the second, crepuscular or 

 nocturnal animals requiring protection from glare during daylight 

 (Figs. 607-10). 



The following have vertically oval pupils : 



Many Carnivora — the larger Feliclse (lion, tiger, leopard, jaguar) ; Canidfe 

 (dog, fox, etc.) ; most hyaenas, and Viverridfe ; ainong the Procyonidfe, the 

 panda ; some Ursidfe (the arctic white bear, Thalassarctos maritimus, and 

 Melursiis (Fig. 609) ). 



Few- Rodents — the varying hare {Lepus timidus), the nutria-bearing coypu 



