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



modation considerable, but slower than in the Owl ; in the Buzzard the 

 range of vision is greater still, and the power of accommodation capable of 

 being readily and extensively exercised. 



These conclusions, I think, will be found to accord with the observations 

 of those who have had opportunities of making themselves acquainted with 

 the habits of the birds during life. 



It has been usual for those who have devoted much attention to the 

 physiology of vision to propose some original and independent explanation 

 of the means by which accommodation for distance is effected, if their 

 researches have been attended with the observation of any previously un- 

 known facts connected with the subject, either experimental or anatomical. 

 It appears to me that as yet we have not sufficient data to afford a per- 

 fectly satisfactory explanation of that remarkable property possessed by 

 the eye, partly on account of the difficulty of ascertaining the exact func- 

 tions of different structures, and particularly by reason of the very various 

 conditions which the same structures assume in various species of verte- 

 brate animals. The line of investigation which is pointed out in this com- 

 munication it is by no means certain will assist in the solution of the pro- 

 blem of the means by which adjustment for distance is effected ; but I am 

 inclined to think that we have not yet exhausted all the resources which 

 careful anatomical inquiry places at our command, and that when a suf- 

 ficient number of details have been collected, the subject will be in a more 

 suitable state for the application of optical laws than it is at present. 



Supplement, containing a Description of the Eye in Rhea americana, 

 Phoenicopterus antiquorum, and Aptenodytes Humboldtii. Re- 

 ceived April 27, 1872. 



In the American Ostrich the eye is large, and the structures concerned 

 in the adjustment for distance are well developed. In the Ostrich (Stru- 

 thio camelus) the observation was first made by Sir P. Crampton of the 

 existence of the ciliary muscle ; and as the views of physiologists regarding 

 the mechanical functions of the muscle in the accommodation of sight were 

 various, while numerous inquiries were made very soon after the publication 

 of this new anatomical fact, I am gratified in having the opportunity of 

 pointing out the cause of the discrepancies in opinion which have continued 

 to the present time. 



The description which Crampton has given is correct so far as it goes, 

 but it was limited to that part of the ciliary muscle which forms the thickest 

 portion of it, that is to say, the dense part which lies closest to the 

 margin of the cornea. The tendon of the muscle and its insertion into 

 the choroid were not observed by Crampton, and the structure termed 

 the posterior elastic ligament was overlooked. It can thus be explained 

 how it was that the deflection of the margin of the cornea and consequent 



