CH. XXIV] SKELETON OF HIND-LIMBS 613 



FIG. 305. Wing of a Wild Duck, Anas boschas x $. 



A. Eight wing seen from the dorsal side, with the coverts removed. B. Left 

 wing disarticulated and seen from the ventral side, with the coverts 

 removed. C. The dorsal side of a right wing. D. The ventral side 

 of a left wing. From Wray. 



lu A and B. 1. Humerus. 2. Eadius. 3. Ulna. 4. Eadial carpal. 

 5. Ulna carpal. 6. First phalanx of first digit. 7. Second metacarpal. 

 8. Third metacarpal. 9. First phalanx of second digit. 10. Second 

 phalanx of second digit. 11. Vestigial quill. 12. Tertiaries. 



13. Secondaries. 14 17. Primaries. 



In C and D. 1, 2, 3, 5, and 7. Coverts. 4. Bastard wing. 6. Primaries. 

 8. Secondaries. 9, 10. Tertiaries. 



manoeuvre birds are assisted by the tail, which is really a fan- 

 shaped row of strong feathers attached to the coccyx, that very 

 small vestige of a true tail or portion of the vertebral column 

 extending behind the anus, which modern birds possess (Fig. 307). 

 In this region the vertebrae are thin discs, several of which may be 

 soldered together so as to form a bone called the pygostyle. 



FIG. 306. Lateral view of the pelvis and sacrum of a Duck, Anas boschas x f . 



1. Ilium. 2. Ischium. 3. Pubis. 4. Pectineal process, the rudiment 

 of the prepubis corresponding to the pubis of the Lizard. 5. Ace- 



tabulum. 6. Ilio-ischiatic foramen. 7. Fused vertebrae. 8. Facet 

 on which the projection on the femur, the trochanter, plays. 



The legs of birds can be shown to be constructed on essentially 

 the same type as those of Reptiles, but modified so as to 

 enable them to support the body in an upright position. 

 The arrangements to effect this are very interesting, 

 as they differ markedly from those found in the human skeleton. On 

 the other hand they agree with the modifications of the hind limb 

 found in those extinct Dinosauria which were bipedal. 



In the pelvic girdle the ilia are lengthened so as to be 

 attached to a considerable number of vertebrae, six or more, and 

 so a firm attachment of the limb to the main skeleton is effected. 



