198 PHYSIOLOGY. 



of looking on one at a distance ; but it is not necessary 

 actually to look at any object in either case, nor do I attempt 

 it. If this does not prove that the muscles of the iris are 

 somewhat under the control of the will, then it cannot be 

 proved that any muscles of the body are so. 



14. |The iris, in the lower animals, not only presents 

 great diversities in colour, as has been stated, but also in 

 form and mobility. In birds, and in the cat tribe, its mo- 

 tions are free and evidently voluntary ; but in reptiles, its 

 motions are obscure ; and in fishes imperceptible. In rumi- 

 nants, in the horse, the marmot, in the whale tribe, and in 

 owls, the goose, and the dove among birds, the pupil is elon- 

 gated transversely or sideways. In the horse, a small square 

 curtain hangs down, which intercepts a great portion of the 

 rays coming from above. In the cat tribe, including the 

 lion, the tiger, leopard, the lynx, the jaguar, &c. the pupil is 

 elongated vertically, as it is also in the crocodile* Now we 

 see a wise design in this arrangement, for in such animals as 

 have to watch their prey, which is generally placed more 

 above them, as on a tree, than at either side, the pupil is 

 elongated vertically, so as to admit of more extended vision 

 in such direction ; while in timid animals, like the ox, sheep, 

 and hare, who have to guard against the insidious approach 

 of enemies, while quietly grazing the fields, we find this ar- 

 rangement reversed, and the pupil admits the greatest num- 

 ber of lateral rays. 



15. Ciliary Processes. These are little folds or fringes of 

 the choroid coat, which, joining the sclerotica near the cornea, 

 (which union is termed the ciliary ligament) turn backwards 

 and inwards, in the form of a circular, plaited fringe, the lit- 

 tle threads of which are called the ciliary processes. They 

 are covered, like the choroid, with the black pigment, and 

 closely embrace the margin of the crystalline lens, forming 

 round it an opaque blackened partition, which absorbs all the 

 side rays of light, which might otherwise have disturbed the 

 clearness of vision. These threads or processes are plaited 



