WINGS AND LEGS OP BIRDS. 



371 



from the earth, it first springs from its feet, spreading its 

 wings in such a manner 

 as to be able to strike the 

 air before falling back on 

 the ground. Those that 

 have very long wings, 

 require more space to de- 

 press them ; and if, there- 

 fore, their feet are too 

 short to allow them to 

 spring very high, they ' 



find it difficult to raise c b 



themselves at first. The Fl - 183. WING OF SPARROW-HAWK. 



Swallows are examples Of a, third primary; 6, ninth primary ; c, second- 



, aries. 



this. 



334. The feathers of the tail also are useful to Birds, to 

 direct them in their flight ; they spread and raise them, or lower 

 them, like a rudder, to increase or diminish the obliquity of their 

 upward course : and by inclining them to one side or the other, 

 they are aided in changing their direction. 



335. When the Bird rests on the ground, the posterior 

 members alone serve to support it ; it is then truly a biped ; and 

 as such it requires a broad pelvis firmly fixed on the vertebral 

 column. The iliac (hip) bones are much developed in Birds ; 

 and form only one piece with the lumbar and sacral vertebras. 

 This bony circle is generally incomplete in front ; the pubic 

 bones not meeting on the central line. The thigh bone is short 

 and straight ; and the leg is composed, as in most of the 

 Mammalia, of a tibia, a fibula, and a patella; but the two 

 first of these are united together towards their lower extremities. 

 A single bone, which forms a continuation of the leg, represents 

 the tarsus and metatarsus ; and bears at its inferior extremity 

 the toes, which are usually to the number of four. They are 

 never more numerous; but sometimes the external, or the 

 internal finger, or even both, disappear, so that only three (Fig. 

 184), or even two remain (Fig. 185). Three of the four toes 

 are usually directed in front, while the fourth is turned backwards 



BB2 



