[Extract from the "Proceedings" of the Yorkshire 

 Philosophical Society^ 



On the Sclerotic Ring of the Eyes of Birds and Reptiles. 

 By THOMAS ALLIS, ESQ. Read April, 1849.* 



When I began the preparation of Bird's Skeletons, I was not 

 aware that their eyes were furnished with this bony apparatus, 

 and when first informed of the fact, it was mentioned only with 

 reference to rapacious birds. 



By accident the sclerotic bones of an Eagle Owl became 

 detached from each other in consequence of over boiling ; I was 

 induced to articulate them together and to count them ; and on 

 finding it stated in Cuvier's Comp. Anatom. that the usual 

 number of these bones was twenty, whereas in the bird in ques- 

 tion they only amounted to fifteen, I was led to proceed further, 

 and after dissecting minutely the sclerotic ring of upwards 

 of seventy birds, taken from every great division, the greatest 

 number I have found in any instance is seventeen ; and the 

 smallest number eleven ; except in a single instance, in which 

 the ring is composed of but one single bone. I have sixty-seven 

 species on these tablets : of these, the ring consists in one 

 instance of only a single bone ; three have eleven bones ; eight 

 have twelve ; twelve have thirteen ; twenty have fourteen ; 

 nineteen have fifteen ; two have sixteen ; and two have seven- 

 teen. I have consulted several authors, but have met with little 

 respecting either the bones themselves or their functions ; the 

 little I have found is contained in the following extracts ; after 

 giving which, I shall mention concisely those particulars in 

 which the results of my own researches differ from the state- 

 ments made by these authors. 



Blumenbach Comp. Anat., 296, says, " the eyes of birds of 



* This paper was composed in 1837, and in that year was read to the British 

 Association assembled in Liverpool. At the request of the Yorkshire Philosophical 

 Society, in whose Museum the Allisian Collection of Comparative Osteology is 

 preserved, it was read to that Society in 1849. In the interval between these dates, 

 Mr. Allis had the satisfaction of shewing to the authors of that splendid publication, 

 4 The Dodo and its Kindred,' that their inference of the place of Dodo among tho 

 Columbidse was entirely confirmed by the independent evidence of its Sclerotic 

 Bones. (Note by Editors.) 



