356 



Dr. R. J. Lee on the Sense of Bight in Birds. [May 16, 



have found that rupture of the ligament usually takes place, I presume from 

 its tenacity being destroyed by the action of the fluid. It is on that part 

 of the choroid which lies between its two lines of attachment, on its in- 

 ternal surface, that the ciliary processes are developed, and to the anterior 

 part of those processes that the crystalline lens is attached. Contraction 

 of the ciliary muscle, it is reasonable to suppose, would produce a change in 

 the position of the lens, and would take place when the object to which 

 the sight was directed was close to the eye — that is to say, the muscle is 

 employed in accommodation for short range of vision. The position of 

 rest is restored by the posterior elastic ligament, which acts in direct op- 

 position to the muscle. 



The eye of the Vulture is smaller than that of the Owl, is not so de- 

 cidedly pyramidal in shape, and may be placed between the latter and the 

 eye of the Buzzard. The chief difference, however, between them is in 

 the greater degree of concavity which the posterior portion of the sclerotic 

 assumes ; so that in the Owl the retina lies on a natter surface than in the 

 Buzzard, while in that respect the Vulture is between the two. 



The dimensions of the eye of the Vulture are as follow : — 



in. 



Diameter of cornea 



Lateral diameter of the sclerotic in its broadest part . 1 



1 6 



Antero-posterior diameter of eye 



9 



Length of ciliary muscle 



Breadth of the posterior elastic ligament 



Length of the anterior elastic filaments approximately the same. 



With regard to the anterior elastic filaments and the posterior elastic 

 ligament, it is unnecessary to make further remark, beyond that they re- 

 semble those structures in the eye of the Owl. 



In the Buzzard the dimensions of the eye and its structures are as 

 follow : — 



in. 



Diameter of cornea . , T 4 -^ 



Lateral diameter of eye 1 



Antero-posterior diameter of eye f 



Length of ciliary muscle < -f^ 



L ength of posterior elastic ligament 1 x 



Length of anterior elastic filament J 1H 



In order to ascertain the mechanical effect produced by the ciliary 

 muscle, the simple experiment may be performed of applying traction, by 

 means of a pair of forceps, on the choroid, the dissection being arranged 

 and fixed as I have described. It will readily be seen that the elastic 

 ligament acts in direct opposition to the muscle, and in the living eye has 

 the power of restoring the parts to the condition of rest. 



The ciliary muscle is composed of striated fibre of very distinct character. 



