FREE APPENDAGES BIRDS 



287 



former has a strong cnemial crest (fig. 310, c). Tibiale and intermedium are 

 fused (astragalus, talus) the pisiforme sometimes being included in this bone. 

 Its intermediate part extends up on the lower end of the tibia, fusing with it in 

 Triceratops. In some species the calcaneum projects like a heel. The tarsaha 

 persist in part in some Stegosaurs. The digits vary between three and five, and 

 the phalanges are very variable in number. 



Pterosauria. — The limb skeleton of the wings differs from that in other 

 flying Vertebrates (birds and bats). The moderate humerus has an expanded 

 deltoid crest. Radius and ulna, about equal, are sometimes 

 twice the length of the humerus, and their ends are but little 

 expanded. The carpal bones are in two rows, the proximal 

 with two ossicles, while the three or four carpalia are some- 

 times fused. Apparently the first metacarpal is lost, the 

 remaining four are subequal, (sometimes as long, sometimes 

 half as long as the fore arm, but the fifth is much stronger than 

 the others which may be reduced to mere threads. The fifth 

 supports the greatly elongate fifth finger which is the main 

 support of the bat-Hke wing. Metacarpals 2 to 4 bear the 

 small digits of the corresponding fingers which are free from 

 the wing. The femur has a weak trochanter. The tibia, as 

 in birds, is longer than the femur, but the fibula is reduced, 

 its pointed lower end reaching to about the middle of the 

 tibia, with which it may fuse. There are two proximal tarsal 

 bones, sometimes fused with the tibia. There are at least three i /' 



tarsalia and five metatarsals, the fifth short and sometimes 

 bearing no phalanges. 



Fig. 310. — Hind 

 foot of Megacerops 

 tyleri (Lull, ' 05). 

 F e , femur; F , 

 fibula; T, tibia. 



AVES. — Although very different in external 

 appearance and in use, the wing and leg of a bird are 

 much ahke in structure, and what differences occur 

 are largely confined to the distal parts which, in the 

 wing, have been more modified than in the leg. 

 Reduction has 'gone so far that in some fossils no 

 trace of a wing has been found, while many moas 

 lack a humerus. 



In all recent birds the humerus is long and slender (fig. 311), its 

 proximal end expanded and having a rather long articular surface 

 which fits in the glenoid fossa. Both radial and ulnar tuberosities 

 (sometimes long crests) are present, the ulnar containing the opening 

 to this highly pneumatic bone. The two distal articular surfaces 

 are separated by a groove, most marked on the palmar surface, 

 Paseres often have a brachial patella between humerus and fore 

 arm. 



