144 Royal Society : — 



in small species of birds to considerably less than an inch, that the 

 action of the muscle is exerted. 



The exact functions performed by the ciliary muscle in all those 

 vertebrata in which it exists are still undecided ; but it is not difficult 

 to reconcile the accounts which have been given by different anato- 

 mists of its structure, if we are aware of the fact that the muscle 

 does not possess the same characters in all classes of animals — 

 indeed, that it is not precisely the same in those that are very nearly 

 allied ; so that it is important, particularly in the case of birds, as 

 will be seen, to mention the species under consideration. 



It may be stated generally that in birds it is developed in a re- 

 markable degree ; in fish it is entirely wanting ; in the mammalia it 

 varies directly in proportion to the powers of sight possessed by the 

 species, except in the feline class and in those animals which enjoy 

 the power of nocturnal vision, and in which the ciliary muscle is 

 peculiarly large and difi'erently developed from the same structure in 

 other mammals. 



The three specimens which are to be described belong to the Eagle 

 Owl, the Egyptian Vulture, and the Buzzard. They were brought 

 from Egypt by a gentleman who shot the birds himself, and removed 

 the eyes while in the fresh state, preserving them in spirit of wine 

 till he sent them to me. 



The eye of the Eagle Owl presents in the most striking degree the 

 peculiar characters of the class to which it belongs. The first of 

 these are its shape and size, too well known to require description, 

 adapted as they are to the very shallow cavities of the orbits. 



In the Egyptian Vulture the pyramidal shape of the eye is less 

 remarkable, and a slight approach is observable in it to the spherical 

 globe. In the Buzzard this is still more marked, and the eye resembles 

 as much the eye of the Pigeon as it does that of the Eagle Owl. 



In examination of specimens which have been preserved in spirit, 

 it is necessary to restore the pliancy of the tissues of the ciUary 

 muscle by allowing them to remain in water for some days ; and I 

 may observe that as this condition must be obtained in order to 

 make satisfactory preparations, the method of using solutions of 

 chromic acid or bichromate of potash to enable the anatomist to 

 make sections is not to be recommended, if the object be to ascertain 

 the dimensions of the muscle and the elasticity of the ligament, which 

 will be presently described. It need hardly be stated that the best 

 mode of treating the eye is to freeze it and then make sections. 



The strong plates of bone which exist in the sclerotic of birds 

 preserve the shape of the eye sufficiently well to allow of the dimen- 

 sions being ascertained after it has been preserved in spirit. 



In the Eagle Owl the dimensions are as follow : — 



in. 



Diameter of cornea ^ 



Diameter of base of eye 1 ^^ 



Antero-posterior length ly^ 



Lateral diameter of lens y^ 



Antero-posterior diameter of lens \ 



