14 BONES OF THE EXTREMITIES. 



These double clavicles maintain the shoulders apart in spite of 

 the violent force applied in a contrary direction by the exercise 

 of the wings, which is greater the stronger the flight. 



12. The wing of the bird corresponds to the anterior extremity 

 of mammals, and is also composed of three principal parts, 

 namely : the arm, the fore-arm, and the hand. The arm con- 

 sists of a humerus which is not particularly remarkable; the 

 fore-arm which consists of a radius and an ulna, corresponds in 

 its length with the strength of the flight of the bird ; and the 

 hand is reduced to a sort of stump, which serves for the insejr- 

 tion of the large feathers of the wing : there is distinguished a 

 range of carpal bones, a bone in the form of a style which rep- 

 resents the thumb, a single metacarpal bone sustains a finger 

 with two phalanges, and the vestiges of a third finger which is 

 represented by a small styloid bone. 



13. The lower extremities of birds are designed solely for 

 support and for walking ; sometimes they become the organs of 

 natation, and there are some of these animals that employ them 

 for the prehension of aliment. The bones of the haunches are 

 strongly developed ; they are attached to the neighbouring part 

 of the vertebral column, so as to form with it a single piece, and 

 the bony belt which results from this assemblage, and which is 

 called the pelvis, remains almost always incomplete in front. 

 The femur is short and directed forward ; the tibia is strong, and the 

 fibula is reduced to a mere bony style. The tarsus and metatarsus 

 are represented by a single bone, the length of which determines 

 the height of the bird on its legs. The number of toes varies 

 from four to two ; almost always there are three directed for- 

 ward and one backwards. The number of phalanges ordinarily 

 increases from two to five, from the hind toe or thumb, to the 

 fourth toe. We therefore count two phalanges for the thumb or 

 great toe, three for the internal toe, four for the middle toe, and 

 five for the external. 



14. In swimming birds the toes are palmate, that is, united by 

 membranes sufficiently broad to allow them to separate from each 

 other, and when spread, to form a sort of paddle. In those that 



12. How does the wing of a bird differ from the anterior extremity of a 

 mammal ? How does the hand resemble that of a mammal ? 



13. To what purposes are the lower extremities applied ? How does the 

 pelvis of birds differ from that of mammals? Is the fibula complete in 

 biids ? How are the tarsus and metatarsus formed ? What is the number 

 of toes ? How many phalanges have the toes ? 



14. How are the feet of swimming birds characterised ? What is remark- 

 able in the feet of climbing birds ? How are the feet of wading birds dis- 

 tinguished ? How is it that birds can sleep while standing on the limbs of 

 trees without falling ? 



