BIRDS. 203 



enlarged by a salient process in its middle. It is originally composed of 

 live pieces : a middle one, of which this salient lamina makes a part ; two 

 triangular, anterior, lateral ones, for the articulations of the ribs, and two 

 posterior, which are lateral and bifurcated, to increase its surface. The 

 greater or less degree of the ossification of the notches of these last, and 

 the interval they leave between them and the principal bone, determine 

 more or less the flight in birds. The diurnal Birds of prey, the Swallows 

 and the Humming-birds, lose, as they grow old, all traces of these un- 

 ossified spaces. 



The /o?<rc/?e<?e produced by the junction of the two clavicles, and the 

 two powerful stretchers formed by the coracoid apophyses, 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 vigorous is the fourchette. The wing, supported by the humerus, 

 fore-arm, and by the hand, which is elongated, and has one finger and the 

 vestiges of two others, is furnished throughout its length with a range of 

 elastic quills, which greatly extentls the surface that resists the air. Those 

 quills which belong to the hand are termed primaries, and there are always 

 ten of them ; 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 bastard 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 Gallinacae 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 extension 

 without any eff'ort on the part of the muscles. The tarsus and metatarsus 

 are represented by one single bone, terminating below in three puUies. 



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 external 

 toe, which has five. 



Birds are generally covered with feathers, a 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 hold in the bones, the place of the marrow, 

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

 portion of the ribs is ossified, in order to give more power to the dilatatiori 



