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Dr. John Davy on the Bones of Birds. [Dec. 6, 



heated in alcohol, it was partially dissolved, the solution becoming turbid on 

 cooling. Evaporated, and as seen under the microscope, the residue, pro- 

 portionally small, seemed to consist chiefly of fatty and oily matter (stearine 

 and olein ?), with some needle crystals. 



XII. 0/ the Blue Tit. — Of a young one taken from the nest on the 

 31st of May, then weighing 2S'5 grs., quite naked, except a few delicate 

 fibre-like feathers on the head, some yolk still remaining in the abdominal 

 cavity, the humeri were very small and pale, so small that no attempt was 

 made to examine them, except by crushing. Comminuted with a few 

 drops of solution of salt, and subjected to the microscope, there were seen 

 mixed with the fragments of cartilage, blood-corpuscles and oil-like globules. 



2. Of a young one, nearly fully fledged, which on the 3rd of August 

 weighed 142 grs., the humeri sank in water, maintaining a perpendicular 

 position. They were completely formed and well ossified. Excepting 

 towards their inferior extremity they were white, there to a small extent 

 they were red. The white portion, at least nine-tenths of the entire 

 length, contained air; the red, not exceeding one-tenth, marrow which, 

 as seen under the microscope, had all the character of medullary tissue 

 and abounded in oil. 



3. Of a third, shot in the same place as the preceding, and probably of 

 the same brood, which on the 18th of August weighed 179'5 grs., the 

 humeri floated in water, and were entirely full of air. The feathers of the 

 abdomen were not fully formed, and the bursa Fabricii was much smaller 

 than that of the preceding. 



From these results, may not the following conclusions be drawn ? 



First, that at an early stage, and up to a certain period of growth, 

 marrow exists in the bones specified, of all the birds first named ; and 

 that about the time of hatching the medullary tissue abounds less in oil 

 or fatty matter than at a later, the proportion varying in different in- 

 stances ; least probably in birds of prey, such as the buzzard and owl ; 

 most in birds, the food of which is mostly vegetable, such as the goose. 



Secondly, that the substitution of air for marrow in those bones which 

 are eventually hollow, varies as to time in different species ; is earlier in 

 the rook, the crow, the grouse, the tit, than in the common fowl, 

 duck, and goose, especially the latter ; the exchange of one for the other 

 having probably some relation to the time of taking wing and the use of 

 the parts ; and, in accordance, the humeri, except in the instance of the 

 sparrow-hawk, seemed to have the marrow absorbed somewhat earlier than 

 the femora. It may be conjectured that, like the residual yolk in the 

 young bird, the marrow in the bones in question may serve in part as food, 

 nourishing in the act of its removal. 



Relative to the structure of the hollow bones, I have but a few words to 

 offer. 



