2 



prey have a peculiar form ; which is similar to that of the 

 chalice or cup used in the communion service ; the cornea which 

 is very convex forms the bottom of the cup, and the posterior 

 segment of the sclerotica resembles the cover; this peculiar 

 form arises from the curvature and length of the bony plates, 

 which, as in all other birds, occupy the front of the sclerotica, 

 lying close together and overlapping each other; these bony 

 plates form in general a slighty convex ring ; being long and 

 curved in the Accipitres, they form a concave ring, which gives 

 the whole eye-ball the above-mentioned form." 



Dr. Albers observes, " that the orbit is very imperfect in 

 birds, and that this bony ring may supply the deficiency." 



Carus says, " the firm and elastic sclerotica of birds, the 

 structure of which has been very accurately examined by 

 Albers, consists of three laminae, between the outer and middle 

 ones of which the osseous circle is inserted anteriorly. This 

 structure, which already exists in some fishes and amphibia, is 

 common to all the species of birds ; it is composed of from 

 fifteen to seventeen oblong quadrangular laminae of bone, with 

 the corners rounded off; forming in some cases simply a smooth 

 circle, in others a more or less prominent cylinder ; in Owls this 

 cylinder is particularly long." 



Cuvier says, {f the sclerotic of birds is divided into laminae, 

 the interval of which receives a circle of small, thin, hard, 

 oblong bones, which lie over each other like tiles, and which 

 give to the anterior part of the eye a great degree of firmness 

 and a fixed form. These ossicula are almost flat in the greater 

 number of birds ; in which they form only an annular disk of 

 little convexity ; they are slightly arched and concave externally 

 in the Horned Owl, in which they form a short tube in the form 

 of a truncated cone ; they are usually twenty in number." 

 Cuvier further states, that " the sclerotica determines the shape 

 of the eye ; it can therefore be really soft and flexible only in 

 animals that have the eye nearly globular ; that is to say in 

 man and quadrupeds ; because their sclerotic assumes of itself 

 that shape, in consequence of the nearly uniform resistance 

 made by the fluids contained in the eye to the pressure of its 



