114 AYES. 



trary, which serves as a fulcrum to the wings, has but little mobility ; 

 the sternum, particularly, to which are attached the muscles which 

 lower the wings in flight, is of great extent, and has its surface still 

 more enlarged by a salient process in its middle. It is originally com- 

 posed of five pieces. The greater or less degree of the ossification of 

 the notches, and the extent of the interval they leave between them 

 and the principal bone, denote a relative strength of wing and power of 

 flight. The diurnal birds of prey, the swallows, and the humming- 

 birds, lose, as they grow old, all traces of these unossified spaces. 



The fourchette produced by the junction of the two clavicles, and 

 the two powerful stretches formed by the coracoid apophysis, keep the 

 shoulders apart, notwithstanding the efforts requisite for flight, that 

 act in an opposite direction ; the greater the power of flight, the more 

 open and strong is the fourchette. The wing, supported by the 

 humerus, fore-arm, and hand, the latter of which is elongated, and has 

 one finger and vestiges of two others, is furnished throughout its length 

 with a range of elastic quills, which greatly extends the surface that 

 resists the air. Those which belong to the air are termed primaries, 

 and there are always ten; those attached to the fore-arm are called 

 secondaries ; but their number varies ; weaker feathers appended to the 

 humerus are called scapulars; the bone, which is analogous to the thumb, 

 is also furnished with what are termed spurious quills. Along the base 

 of the quills is a range of feathers named coverts. 



The bony tail is very short, but has a range of large quills, which, 

 when spread out, assist in supporting the bird ; they are generally twelve 

 in number, sometimes fourteen, and in the gallinaceae eighteen. 



The legs have a femur, a tibia and a fibula, which are connected with 

 the femur by an articulation with a spring, which keeps up the exten- 

 sion without any effort on the part of the muscles. The tarsus and 

 metatarsus are represented by one single bone, terminating in three 

 pulleys. 



Most commonly there are three toes before, and a thumb behind ; the 

 latter being sometimes deficient. In the martins, it is directed forwards. 

 In the climbers, on the contrary, the external toe and the thumb are 

 directed backwards. The number of articulations increases in each toe, 

 commencing with the thumb, which has two, and ending with the ex- 

 ternal toe, which has five. 



Birds are generally covered with feathers, the kind of tegument best 

 adapted for defending them from the rapid variations of temperature to 

 which their movements expose them. The air cavities which occupy 

 the interior of their body, and even supersede the marrow in the bones, 

 increase -their specific lightness. The sternal, as well as the vertebral 



