1872.] 



Dr. R. J. Lee on the Sense of Sight in Birds. 



357 



It varies, as is seen in the three examples described, in length and amount 

 of muscular tissue. The tendon in the Owl is long and the body of the 

 muscle short ; but in the other species, as in most birds, the muscular 

 fibres extend to a great length, if not entirely from the origin to the in- 

 sertion of the muscle. These minute differences should be pointed out in 

 detail in the case of each species of bird. 



The elastic ligament is composed of very delicate elastic tissue, the micro- 

 scopical character of which is well defined. 



On the peculiar nature of the anterior elastic filaments I beg to postpone 

 any decided opinion. 



With regard to the nerves which supply the ciliary muscle and the iris, 

 I have no particular remarks to offer, as the description which I gave 

 some years ago of the ganglia and plexuses on the ciliary nerves in the 

 eve of the Pheasant will apply generally to all birds. "Whether the con- 

 traction of the iris and the accommodation of the sight be voluntary or 

 involuntary actions on the part of birds we cannot say positively ; I am in- 

 clined to believe that the latter is the case. 



For the sake of convenience, and to render any further researches on 

 the dimensions of the different parts of the eye in other species of birds 

 symmetrical with those contained in this communication, I have arranged 

 the principal facts in the following tabulated form :— 





Eagle Owl. 



Egyptian 

 Vulture. 



Buzzard. 



Diameter of cornea 



•875 



•506 



1 



Greatest diameter of sclerotic (trans- 











1-312 



1-182 



1 









1-375 



•932 



•75 





•506 



2sot recorded. 



•343 





•5 





•22 





-375 



■3 



•187 



Brcadth of posterior elastic ligament 



•125 



•1 



•063 



Length of anterior elastic filaments . 



125 



•1 



•063 





Body short, 



Muscular 



Muscular 



tendon long. 



fibres form 



fibres extend 







more than 



from origin 







three fourths 



to insertion. 







of it. 





From the above Table we may draw the following conclusions : — that in 

 the Eagle Owl the range of vision is small, the power of accommodation 

 very rapid ; in the Vulture range of vision is great, the power of accom- 



