THE PLACENTALIAN EYE 681 



it is this which the ciliary body must be thought of as surrounding. They 

 number about 50-100 in carnivores, 60-100 in seals, 90-130 in ungulates 

 and whales, and up to 135 in large-eyed rodents and lagomorphs (hares, 

 beavers). A ciliary web is often present (see Fig. 194b, p. 667); and, 

 in a vestigial condition, it can be made out in man. The tips of the ciliary 

 processes touch the lens in a number of mammals, but they are never 

 fused with it and probably never exert any effective pressure on it in the 

 few mammals which have useful accommodation (primates, squirrels, 

 large carnivores). The mechanics of mammalian accommodation are 

 entirely unlike those of the sauropsidan process, and the difference may 

 be wholly ascribed to the fact that the primitive mammals allowed a 

 'circumlental space' to be opened up between the ciliary processes and the 

 lens, when they threw away the ossicular ring of their reptilian forebears. 



Two chief types of processes are distinguished. The more primitive 

 type is puffy and rugose, like that in monotremes (Fig. 194b, p. 667; 

 cf. Fig. 6c, p. 14) . This type occurs in all of the lower orders and also 

 in some of the highest — the artiodactyls and perissodactyls, for example. 

 A more specialized type, whose differences from the other have no 

 known functional significance, is the thin, smooth-surfaced, 'knife-blade- 

 like' process seen in most carnivores and pinnipeds and in some primates 

 (Fig. 197a). This type has also been evolved by the higher marsupials 

 (Fig. 196b, p. 673). 



The two kinds of ciliary processes are associated with fundamental 

 differences in the organization of the zonule which are perhaps related 

 to the extent of accommodation. In forms with thick processes, some of 

 the zonule fibers arising from the inner surface of the base-plate run for 

 a space along the floors of the valleys between the processes, and others 

 run alongside the faces of the processes. As all these fibers curve out 

 toward the lens, they are quite uniformly distributed both in the aspect 

 of a sagittal section and in the view of the zonule obtained by removing 

 the cornea and iris from a gross specimen. The attachments of the fibers 

 to the periphery of the lens are uniformly distributed both circumferen- 

 tially and meridionally (Fig. 197d). One cannot speak here of anterior 

 and posterior 'leaves' of the zonule, for there is no canal of Hannover. 



The greatest contrast with this situation is seen in the carnivores, as 

 exemplified by the domestic cat, studied by Kahmann. Here the ciliary 

 processes are knife-like, and between every two major ones there is a low 

 secondary process. Zonule fibers arising from the orbiculus segregate 

 into paired bundles as they enter the ciliary valleys, and those in each 



