3io BIRDS. 



surface at which they procure their food. The number of the 

 bones in the neck is consequently very variable : the swan has 

 twenty-three, and the sparrows only nine ; and their joints are 

 50 disposed that the neck may be bent in the form of the letter S, 

 and, consequently, elongated or shortened in proportion as the 

 curves are diminished or increased. The trunk of a bird is an 

 admirable piece of mechanism, combining elasticity and strength 

 with the utmost compatible degree of lightness. He is but a bung- 

 ling mechanic who makes an unnecessary waste of material : the 

 triumph of mechanism is to obtain the greatest possible firmness 

 at the least cost of substance ; and whoever examines the chest 

 of a bird will at once acknowledge the transcendent skill evinced 

 in every part of its construction. The bones of the back (3), which 

 sustain the ribs, are immoveably fixed to each other ; the ribs (5), 

 of the lightest structure, are locked together by overlapping plates 

 while the breast-bone (6) not only constitutes a broad shield or 

 breast-plate, but is furnished with a deep crest or keel, from whence 

 the muscles employed in flight take their origin. Birds having 

 this shield largest and most complete are those that fly the best. 

 The bones of the shoulder (7, 8) are disposed in a manner most 

 favourable to the support of the wings, and the two collar-bones 

 (7) are joined together so as to form but one piece, having the 

 shape of the letter V an arrangement well calculated to hold the 

 shoulders apart, in spite of the violent force applied in the contrary 

 direction by the exercise of the wings, a force that increases with 

 the energy of the muscles employed in flight The wing of a bird 

 corresponds to the human arm, and, like it, is composed of three 

 principal parts the arm, the fore-arm, and the hand. The bone 

 of the arm is of great strength and lightness, being constructed 

 upon the principle of a hollow cane. The fore-arm consists of two 

 bones, the length of which is in relation with the power of flight, 

 while the hand is reduced to a single piece, that serves for the 

 support of the large feathers of the wing ; there are also a rudi- 

 mentary thumb and the vestiges of a third finger. 



The legs of a bird are designed for support and for progression ; 

 sometimes they are constructed for swimming, and are frequently 

 employed for the purpose of seizing or holding food. The bones 

 of the haunches (14) are of great strength, and solidly fixed to the 

 vertebral column. The thigh-bone (15) is short and directed for- 

 ward ; the leg (IG) is strong and composed of but one bone; while 

 the bones of the foot and instep (17) are represented by a single 

 piece, the length of which determines the height of the bird on its 



