31 



STRUCTURE OF BIRDS. 



BIRDS are described by CUVIER as " Oviparous, vertebrated 

 animals, with double circulation and respiration, organized for 

 flight. Their lungs are not divided, but fixed to the ribs, and 

 are enveloped in a membrane pierced by great holes, which per- 

 mit the air to pass into many cavities in the chest, lower belly, 

 arm-pits, and even the interior of the bones ; so that the exterior 

 fluid not only bathes the surface of the pulmonary vessels, but 

 also the surfaces of an infinity of vessels of the rest of the body. 

 Thus, birds respire in some respects by branches of their aorta 

 as well as by those of the pulmonary artery, and the energy of 

 their irritability is in proportion to their quantity of respiration. 

 All their body is arranged to participate in this energy. Their 

 anterior extremities destined to sustain them in flight, could 

 neither serve the purpose of standing or holding ; hence they 

 are biped, and take things from the ground with their mouth : 

 thus their body is inclined before their legs, the thighs carry 

 them forward, and the toes are elongated to form a sufficient 

 base; the pelvis much extended in length, to furnish attach- 

 ment to the muscles which support the trunk on the thighs. 

 There is moreover a set of muscles proceeding from the pelvis to 

 the toes, and passing over the knee and heel, so that the weight 

 alone of the bird closes the toes, and thus they are enabled to 

 sleep perched on one foot. The ischia, and especially the ossa- 

 pubis, are elongated behind, and widen to leave sufficient place 

 for the development of the egg. 



" The neck and the beak are elongated, to reach the ground, 

 and the former has pliability enough to be bent backward when 

 at rest. It has therefore many vertebrae. On the other hand, 

 the trunk, which supports the wings, has very little motion ; the 

 sternum especially, to which are attached the muscles which 

 lower the wings in flight, is very much extended, and has its 

 surface increased, moreover, by a laminous projection in tho 

 middle. It is formed of five pieces ; one central, of which the 

 laminous projection makes a pivot ; two anterior lateral, for the 

 attachment of the ribs ; and two posterior lateral, for the exten- 

 tion of its surface. The degrees of ossification of these last in 

 each species denotes the proportion of vigour for flight. The 

 fu,rca produced by the union of the two clavicles, and the two 

 vigorous supports formed by the c&racoid apophyses, widens the 

 shoulders ; the wing sustained by the humerus, by the fore-arm, 

 and by the hand which is long, and has one digit, and the ves- 

 tiges of two others carries along its whole length a range of 

 elastic quills, which greatly extends the surface which resists the 

 air. The quills adhering to the hand are called primary, and 



