146 Royal Society : — 



side of, the line of insertion of the posterior elastic ligament. The 

 breadth of the latter structure is about one eighth of an inch, while 

 the length of the anterior elastic filaments is nearly the same. Thus, 

 passing from before backwards, we have the anterior elastic filaments, 

 the body of the ciliary muscle, its long delicate tendinous portion, 

 and lastly the posterior elastic ligament. To exhibit the structures 

 satisfactorily, the best plan is to make a section of the choroid and 

 sclerotic of one sixteenth of an inch in thickness, and after fixing the 

 two ends of the section on a layer of cork with needles, to dissect the 

 muscle under water or alcohol — a very simple process if a magnifying- 

 glass of an inch focus is employed. It is only necessary to draw the 

 iris gently away from the sclerotic so as to extend the anterior elastic 

 filaments, fixing it with a needle, and then to do the same with the 

 choroid, taking care to hold that membrane at a point posterior to 

 the line of insertion of the posterior elastic ligament. 



The length of the ciliary muscle is about three eighths of an inch. 

 I have attempted to preserve sections made in this way in Canada 

 balsam, but 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 internal surface, that the ciliary pro- 

 cesses 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 opposition to the muscle. 



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

 decidedly 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 flatter 

 surface than in the Buzzard, while in that respect the Vulture is be- 

 tween 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^ 



Antero-posterior diameter of eye ^ 



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 resemble those structures in the eye of the Owl. 



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

 follow : — 



