364 Professor W. E. Flotver [Feb. 19, 



WEEKLY EVENING MEETING, 



Friday, February 19, 1886. 



Sir William Bowman, Bart. LL.D. F.K.S. Manager and Vice- 

 President, in tbe Chair. 



Professor W. H. Flower, LL.D, F.K.S. Director of tlie British 

 Natural History Museum. 



The Wings of Birds. 



The power of flying through the air is one of the principal 

 characteristics of the cLass of Birds. Although some members of the 

 other great divisions of the Vertebrates— the bats among Mammals, the 

 extinct pterodactyle among Keptiles, the flying fishes among Pisces — 

 possess this power in a greater or less degree, these are all exceptional 

 forms, whereas in birds the faculty of flight is the rule, its absence 

 the exception. Among Invertebrates this power is possessed in a very 

 complete degree by the greater number of insects. 



In the normal structure of the vertebrate animals there are two 

 pairs of limbs, anterior and posterior, never more. It often happens, 

 however, that one pair, and sometimes both, are suiDpressed, being 

 rudimentary, functionless, or entirely absent. Flight is always per- 

 formed by the anterior or pectoral pair, more or less modified for the 

 purpose. The super-addition of wings to arms, as in the pictorial 

 representations of angels, has no counterpart in nature. The wings of 

 the bird, the bat, the pterodactyle, and flying fish, are the homologues 

 of the arms of man, the fore-legs of beasts. In the flying fish the 

 power is gained simply by an enlargement of the pectoral fin, and the 

 function is very imperfect ; in the pterodactyle, by immense elonga- 

 tion of one (the outer) finger, and extension of the skin between 

 it and the side of the body; in the bats, by elongation of the 

 four outer fingers, and extension of a web of skin between them and 

 the body. In the bird the flying organ is constructed mainly of 

 epidermic structures, peculiar outgrowths from the surface, called 

 feathers — modifications of the same tissue which constitutes the hair, 

 horns, scales, or nails of other animals. Feathers are met with only 

 in birds, and are found in all the existing members of the class, con- 

 stituting the general covering of the surface of the body. 



The framework to which the broad expanse formed by the feathers 

 is attached is composed of bones, essentially resembling those of the 

 fore-limb of other vertebrates. The distal segment, manus, or hand, 

 in the vast majority of birds, has three metacarpal bones ^nd digits, 

 the former being more or less united together in the adult state. The 



