MAMMALS 



461 



the pupil relatively immobile, wliile in many species (Ungulates and 

 Carnivores) tlie tendency towards nasal asymmetry of the globe in the 

 interests of binocular vision results in a curtailment of the ciliary region 

 and the practical disappearance of the orbicular zone on the nasal side 

 (Fig. 582). 



The main determinant in the configuration of tliis region is the 

 degree of development of the ciliary muscle^ (FigS- 583-90). Anteriorly 

 the ciliary body splits into two leaves ; one, the outer or scleral part, 

 essentially muscular in structure, hugs the sclera as it runs to the corneo- 

 scleral junction ; the other, sometimes fibrous, sometimes muscular, 



Figs. 583 to 586. — The Ciliary Region in Mammals. 



Fig. 583.— Rabbit. 



Fig. 5S4.— Pi 



Fig. 585. — Dog. 



Fig. 586. — Ape. 



S, the ciliary cleft (or sinus) ; Z, zonular ligament. The ciliary muscle 

 where present is indicated bj' linear shading. 



forming the base-plate of the ciliary body, runs inwards towards the root 

 of the iris (Lauber, 1901) ; between these two leaves lies a triangular 

 cleft of varying depth, the ciliary cleft,- an extension of the anterior 

 chamber which runs backwards deejDly into the ciliary region. In the 

 small-eyed and more primitive Placentals (Rodents, etc.) the ciliary 

 muscle is either lacking or very i-udimentary and probably functionless ; 

 when present it consists of a few slender fascicules lying in much 

 connective tissue in the outer leaf of the ciliary body (Lauber, 1901 ; 

 Colhns, 1921 ; Davis, 1929) (Figs. 583. 587). In these animals the 

 ciliary cleft is small. In Ungulates the muscle is also confined to 

 meridional fibres running close to the sclera, prolonged to find attach- 

 ment to the inner layers of the cornea by the corneo-scleral trabeculae 

 (the cribriform ligament of Henderson, 1921) ; the inner leaf of the 



1 For the innervation, see Pines and Pinsky (1932), Boeke (1933), Warwick (1952). 



2 This formation is often known as the ciliary sinus ; I am using the term ciliary 

 cleft to distinguish it from the ciliary venous sinus. 



