472 



THE EYE IN EVOLUTION 



Vizcacha 



Mongoose 



Weasel 



Coati 



Aard-vark 



{Myocastor coypiis), the S. American vizcacha {Lagostomus trichodactylus), the 

 Patagonian cavy {Dolichotis patagonica), the chinchilla, and the American capy- 

 bara {Hydrochccrus capybara). 



Few Prosimians — Nycticebus and the galago of Zanzibar {Galago zanziharicus) . 



The following Placentals have horizontally oval pupils : 



Among the Ungvilates, all Artiodactyls (Suoidea, Tylopoda and Rviminants), 

 all Perissodactyls (Equidse, Rhinocerotidse) except the Tapiridse (Figs. 607, 

 610). 



All Cetaceans (whales) and Sirenians (sea-cows) except Manatus inunguis. 



Among the Carnivora — a few Viverridae (the mongoose, Herpestes ; Cynictis 

 and Suricata) ; a number of Mustelidse (the ferret, PiUorius furo, the weasel, 

 Mustela nivalis, the ermine, M. erminea, the mink, Lutreola, the wolverine, 

 Gulo) ; among the Procyonidee, the coati (Nasua). Among the Pinnipedes, the 

 bearded seal {Phoca barbata). 



Among the Rodents, the common squirrel {Sciiirus vxdgaris), the African 

 sciuirrel [Xerus), the American chipmunk (Tamias), the prairie-dog (Cynomys), 

 the marmot {Marmot a). 



Among the Tubulidentata, the aard-vark [Orycteropus). 



The direct pupillary reaction to light is generally present (Hertel, 1907 ; 

 K. M. Schneider, 1930 ; Kahmann, 1930-32 ; Rochon-Duvigneaud, 1933 ; 

 Studnitz, 1934 ; Nordmann, 1947) ; a consensvial reaction has been noted 

 in many species (cat, dog, ox, horse, sheep, etc.) (Steinach, 1890-92 ; Schleich, 

 1922). Dilatation to stimuli such as pain or attention occurs in such species as 

 the cat, the dog and monkeys (Macacus) (Levinsohn, 1902 ; Amsler, 1924 ; ten 

 Cate, 1934), reactions particularly evident in the hyjena (Schneider, 1930). The 

 pupils of Ungulates are remarkably insensitive to all stimuli in comparison 

 with those of other Mammals, but the pupils of all Placentals react to atropine 

 (Johnson, 1901). 



The chamiels draiimig the aqueous humour from the angle of the 

 anterior chamber are relativ^ely simple in most Placentals. ^ Associated 

 with the outer wall of the ciliary cleft there is a rich network of veins 

 and venous capillaries which combine to form an intrascleral plexus, 

 the main part of which lies about the level of the middle of the cleft ; 

 this drains outwards by some 5-6 wide scleral veins to the sub- 

 conjunctival veins (Fig. 611). Originally described by Hovius (1716) 

 in the dog, and often called the circle of hovius, this plexus varies 

 considerably in richness and complexity in different animals, being 

 relatively sparse in Ungulates and elaborate in Carnivores. That these 

 vessels are the essential exit -channels of the aqueous humour has been 

 shown by the injection experiments of Nuel and Benoit (1900), Seidel 

 (1923-24) and Kiss(1942-49), and when they reach the subconjunctival 

 plane some of them may contain pure aqueous undiluted with blood 

 (in the rabbit, Schmerl, 1947 ; Weekers and Prijot, 1950 ; Greaves 

 and Perkins, 1951 ; Wegner and Intlekofer, 1952 ; Binder and Binder, 

 IS)^/'^. According to Rohen (1956) in the dog this plexus anastomoses 



(193i 



or literature, see Lauber (1901) 

 rroncoso (1937-42). 



Maggiore (1917), Troncoso and Castroviejo 



