1866.] Dr. John Davy on the Bones of Birds. 305 



In the humeri there is a pecuHarity which may be deserving of mention. 

 Towards the head of the bone, near the pneum.atic foramen, the can- 

 cellated structure, connected m.ore or less by a delicate membrane, per- 

 forms the part of a valve, as indicated by its permitting a free access 

 of air in one direction, but preventing in the other, its exit. Tliis is 

 clearly shown by the use of the blowpipe, and in no instance have I found 

 an exception. 



In the humerus of the common fowl, in three instances (a section of the 

 bone having been made) the air has been found to enter from the pneu- 

 matic foramen by a small bony canal contiguous to the side of the bone, 

 in length about '6 inch, in diameter about '06 incb 



It is said that the trabeculse, or minute columnee in the cancellated struc- 

 ture of the hollow bones, are also hollow. In some of those of the hu- 

 meri of the adult buzzard I have found a canal, but not in others ; these 

 were solid. Nor have I found them otherwise than solid in the humerus 

 of the common fowl, goose, and turkey. 



As to the bones of those birds of the second kind, in which the marrow 

 is persistent through life, I may briefly remark that in them, as in the 

 former, at an early period the marrow seems to be comparatively poor in 

 oily matter ; and that the earlier, the nearer the embryo state, the less is 

 its degree of consistence, the nearer it is to a liquid, and the larger is the 

 proportion of blood-corpuscles and of albuminous matter, and the sm.ailer 

 the proportion of the adipose. 



When mature of growth, the bones of these birds appear to be richer in 

 oily matter than those of the former permanently without air. Thus the 

 tibia of the one kind in the dried state invariably sinks in water, whilst 

 that of the first kind only partially sinks ; the marrow in drying in the 

 latter, from containing less oil, contracting more, and allowing of the 

 entrance of air. In the radius and ulna the difference is less strongly 

 marked ; these bones in their dried state commonly sinking in water, even 

 when belonging to birds of the first kind. 



As regards the quality of marrow in the bones of different birds, the 

 trials I have made have been very hmited. I am disposed to infer from 

 them that, besides differing, as in many instances it does in colour, it 

 may differ also in composition, in the proportion of adipose matter and 

 its kind, and in the proportion of albuminous matter ; in some, as in the 

 bones of the goose, oil most abounding ; in others, as in those of the rook 

 and buzzard, albuminous matter and fat of the stearine kind. Even in the 

 bones of birds of the second kind, such as their long bones, there is a 

 difference in this respect ; of these, all that I have examined sink in water, 

 with the exception of the femora, which only partially sink, the marrow 

 in them being less rich in adipose matter, and consequently in drying 

 contracting more, and, as before remarked, admitting more air. 



* In one instance the same kind of structure was found in the fentiur of a plieasant, 

 VOL. XV. 2 c 



