1865.] Dr. Davy on the Temperature, $c. } of Birds. 449 



*Greenfinch (L. Moris), 

 Yellowhammer (Enteriza citrinella). 

 Gray wagtail (Motacilla boarula). 

 Yellow wagtail (M.flava). 

 Common creeper (Certhiafamiliaris). 

 *Pied flycatcher (Muscicapa atricapilla) . 



* Spotted flycatcher (3/. grisold). 



* Swift (Hirundo apis}. 



* Swallow (H. rustica}. 

 *Martin (H. urbica). 

 *Sand-martin (H. riparia). 



Of the birds in each section, the crania, with some exceptions, contained 

 air. The skull of the water-ouzel is one of the exceptions. It is not cel- 

 lular like that of the majority, but compact and sinks in water. Its greater 

 heaviness may be suitable to the habits of the bird, seeking its prey in the 

 bed of ruuning streams with its head downmost. The same compactness 

 of bone is seen in the crania of the Scolopacidse. This compactness is 

 remarkably contrasted with the cellular state of cranium of certain other 

 birds, in which it is most strongly marked, where lightness as well as power 

 of resistance is needed, such as that of the owls and tits. 



There are certain bones which in the adult stage of the bird appear to 

 be without both marrow and air ; the scapular arch is occasionally an ex- 

 ample of this, especially its posterior wing*, and also the sternum. 



Professor Rudolph Wagner, in his 'Elements of Comparative Anatomy' 

 (English translation), refers to the blackbird and thrush as instances of 

 birds which have air in their femora. I have sought for air in these 

 bones in all the thrushes I have examined, seven different species, but 

 have found only marrow. If verified it would be a curious fact, that in 

 one country air should occur in the bones in question and in another 

 marrow. 



Whether the circumstance of the presence or absence of air in the bones 

 is deserving of attention in the classification of birds, may be worthy of the 

 consideration of the naturalist. In all the tits I have examined, and the 

 number has been considerable, especially of the blue tit, I have never found 

 marrow in the humeri, and the same remark applies to these bones in the 

 larks, but not to those of the pipits. 



2nd. Of the proportions of certain parts of birds as determined by weigh- 

 ing. In the Table which follows a statement is given of results, comprising 

 the weight of the birds examined, of their feathers, and, with a few excep- 

 tions, of their bones, the latter after having been cleaned, deprived of their 

 periostrum, and dried by exposure to the airf. In the first column the 



* The posterior wing in the tabular list is designated scapula, the anterior portion, 

 the coracoid process of some authors, is designated clavicle. 



t In one instance (the bones of the buzzard) it was found, by weighing them before 

 and after drying, that the difference or loss was 12'5 per cent. 



