28S 



ZOOLOGY. 



eagle, and other birds of prey, called base or ignoble, whose 

 wings are truncated at the extremities, can rise vertically 

 through the air. 



In rising from the soil, the bird first springs or leaps from 

 the ground by means of his feet ; if these (the limbs) be too 

 short, as in the case of the martinets, they find it difficult to 

 make the first bound, and seek a declivity to enable them to 

 have room for the expansion and action of their wings. 



Birds in their flight are assisted by the tail feathers, which 

 seem to act as a rudder in directing their course. 



433. When resting on the soil, the bird is strictly a 

 biped, and hence the necessity for a broad and large pelvis, 

 firmly fixed to the vertebral column. The haunch bones are, 

 in fact, extremely developed in birds, and they form, with the 

 lumbar and sacral vertebrae, a single osseous mass (Fig. 222). 

 In general this osseous girdle is incomplete anteriorly ; the 

 bones of the pubis do not unite with each other in front, 

 whilst the ischiatic portions unite 

 with the sacrum, so that the so- 

 called notch in mammals becomes 

 in birds a foramen or hole. The 

 thigh bone is short and straight, 

 and the leg is composed, as in 

 mammals, of a tibia, fibula, and 

 rotula ; but the fibula is united to 

 the tibia before reaching the lower 

 part of the leg. A single bone 

 represents the tarsus and meta- 

 tarsus ; this supports or carries the 

 toes, never more than four in 

 number ; sometimes the great toe 

 disappears, and occasionally the 

 one next it, thus leaving three or 



onl y two < Fi S- 2 . 21 )- The nu mber 

 of the phalanges increases progres- 

 sively from within outwards, from the great toe to the ex- 

 ternal or fourth, from two to five. Finally, of these four toes, 

 three in general are directed forward, the thumb or great toe 

 being turned backwards ; but sometimes the external toe is 

 also turned backwards, as especially in climbing birds, the 

 paroquets, toucans, and woodpeckers, &c. (Fig. 228). 



Whilst the bird rests upon its feet on the soil, it is neces- 

 sary that the centre of gravity fall within the base of susten- 



