MAMMALS 



439 



Fig. 550. — The Ciliary Region of the Wallaby. 



Showing tlie well-formed ciliary processes, the meridional muscle, and 

 the well-formed fibres of the pectinate ligament traversing the deep ciliary 



cleft ( X 60) (O'Day). 



Briicke) arising from the cornea ; more often circular fibres are 

 added anteriorly {Dasijiirus ; the opossums, Marmosa, Dideljihi/s, etc.). 

 The iris is densely j^igmented and richly vascularized with many vessels 

 standing out from the anterior sm'face ; the pupil is round (in Dasynrus 

 viverrinus the contracted pupil is a vertical slit) and a sjDhincter of 

 unstriated muscle surrounds the puijillary margm but a dilatator is 

 absent. In the bandicoot, Perameles, nij>ple- 

 like cystic protrusions of the pigmented retinal 

 layers form flocculi ^ around the pupillary 

 margin. The angle of the anterior chamber and 

 the circumferential ciliary venous sinus are of 

 the mammalian type (Fig. 550). 



The lens is comparatively large, flat in 

 diurnal, round and almost filling the interior of 

 the globe in the smaller nocturnal types ; there 

 are often traces of the amiular j)ad of Reptiles, 

 but it never touches the ciliary processes as is 

 characteristic of Sauropsida. 



The type of retinal vascularization varies. 

 Usually this structure is avascular, and, as if 

 in compensation, the choroidal vessels are so 

 large as to be easily seen ophthalmoscopically 

 (except in some jDhalangers) ; frequently there 



1 p. 469. 



Opossum, 

 Didelphys 



Fig. 551. — The Ciliary 

 Processes of the 

 Kangaroo, Macropus 

 A(uus (after Franz, 

 1911). 



I, iris ; CS, ciliarj' 

 shelf. 



