680 MAMMALS 



delicate strands of uveal tissue which join the base-plate to the sclera. 

 The anterior limit of Fontana's space — its boundary with the anterior 

 chamber (with which it is of course actually continuous, between the 

 strands) — is fixed by the strands or struts which make up the true 

 pectinate ligament : These are heavy connective-tissue fibers, coated with 

 mesothelium, which run from the limbal region of the fibrous tunic to 

 the root of the iris, and support the latter against the tug of the part of 

 the ciliary muscle attached thereto, and the pull of the sphincter during 

 the partial closure of the pupil which ordinarily occurs during accom- 

 modation. The pectinate ligament gets its name from the word 'pecten', 

 meaning 'a comb', and referring to the fact that its strands are like the 

 teeth of a comb which has been bent into a circle with the teeth pointing 

 inward. The strands are best developed in horses, artiodactyls, Orycter- 

 opus, carnivores, and especially in seals (where there may be not one 

 'tooth' but several in a given meridian, forming a fan, somewhat like 

 the situation in reptiles (see Fig. 109, p. 275; Fig. 71, p. 173 [lynx, 

 cougar, dog, dromedary]; and Fig. 150, p. 446). In the horse at least, 

 they appear to be continuous with and identical with the material of 

 Descemet's membrane; and the horse has very similar fibers, with a 

 circumferential course, massed anteriorly in the meshwork of the iris 

 angle. 



In small, large-lensed eyes with very extensive corneae (in murids and 

 similar rodents, armadillos, etc.) the whole ciliary body is reduced great- 

 ly and occupies a relatively narrow zone — sometimes, as in shrews, 

 forming a simple roll without meridional folds or ridges, quite as in the 

 snakes. The uveal meshwork tissue, covering the canal of Schlemm and 

 tapering to meet Descemet's membrane, which so often serves as a 

 tendon of the ciliary muscle, is still present in these eyes; but the 

 ciliary muscle is usually wholly lacking. Fontana's space is either tiny, 

 or else is confluent with the anterior chamber owing to the absence of 

 a pectinate ligament (as also in some large eyes, e.g. the human). Such 

 eyes have no accommodation; and for that matter none has ever been 

 convincingly demonstrated for ungulates — domestic ones, at any rate — 

 despite the presence of considerable tissue of supposedly contractile 

 character. In these small eyes, the ciliary processes are so blobby and 

 irregular that they can scarcely be counted. A very different situation 

 exists in large placental eyes : 



The ciliary processes in large eyes vary in number with the general 

 size of the eye, as in birds — actually, with the size of the cornea, since 



