4S 



ON THE FLIGHT OF BIRDS. 



By JAMES RANKIN, Esq., M.A., Vice-President. 



The following paper on the means of flight of birds, I propose to divide 

 into three sections : — 



1st. The general structure of birds and the relation which it bears tO' 

 the purpose of flight. 



2nd. The special structure of the wings of birds. 



3rd. The mode of action in flight, and some of the specialities in form 

 of wings and feathers and manner of flight. 



Section i. — General Structure of Birds. 



Birds, as a class, are distinguished from other animals by the following 

 peculiarities : — "They are vertebrate animals, breathing atmospheric air by means 

 of lungs ; with warm, red blood, and heart biventriculate and biauriculate, all 

 oviparous, covered with feathers, with bill rather prominent, naked, destitute of 

 teeth. Extremities, four : the anterior changed into wings, and almost always 

 adapted for flying." 



The above, I believe, is a sufficiently comprehensive definition of the class 

 Aves, for it points out how they differ from all other animals, except Fishes, 

 Reptiles, and Mammals, in the possession of backbones ; how they differ from 

 Fishes, in the possession of lungs ; how they differ from Reptiles in having warm 

 blood, and from Mammals in being oviparous. 



The possession of -wings and feathers, though, by far, the most striking 

 peculiarity of Birds, is not of so much classificatory value as might be supposed, 

 for, both among Mammals, ReptUes, and Fishes, are found animals which have 

 wings of some description, as, for instance, the Bats, the Pterodactyl, and the 

 Exocctus or flying-fish, and also some birds have a very rudimentary condition 

 of wings. 



As it is not intended, in this paper, to discuss the question of the 

 systematic position of Birds, I will only mention, in passing, that the morpho- 

 logical afBuities of birds connect them more closely with the class of reptUes 

 proper (i.e., excluding the amphibia) than with any other vertebrates, for birds 

 and reptiles differ from amphibia and fishes, in the absence of bronchise at all 

 periods of their existence, in having a well developed amnion and allantois, and 

 no parasphenoid bone in the skull, and they differ from mammals in having a 

 coaiplex lower jaw, a quadrate bone, nucleated blood-corpuscles, and a single 

 occipital condyle. 



Passing on to the consideration of the structure of birds, we find, with 

 regard to the skeleton, that it is extremelj' light, but that the texture of the 

 bones is firm and close, thereby combining lightness and strength, two important 



