656 



BIRDS. 



There is a well-developed sternum, generally with a keel, 

 with a separate centre of ossification, to which the pectoral 

 muscles are in part attached. The strong coracoids reach 

 and articulate with the sternum. In flying birds the clavicles 



T.M.T 



FIG. 355. Fore-limb and hind-limb compared. 



//., Humerus; R. t radius; U. t ulna; r., radiale ; u., ulnare ; C., distal 

 car pals united to carpo-metacarpus ; CC., the whole carpal region ; 

 MC.J., metacarpal of the thumb ; /., phalanx of the thumb ; MC.II., 

 second metacarpus ; //., second digit ; MC.III., third metacarpus ; 

 ///., third digit.' F., femur; T.T., tibio-tarsus ; /Y., fibula; Pt.> 

 proximal tarsals united to lower end of tibia ; dt., distal tarsals united 

 to upper end of tarso-metatarsus (T.MT.); T., entire tarsal region; 

 MT.L, first metatarsal, free ; I.-IV^ toes. 



are usually well developed, and connected by an inter clavicle ^ 

 which may be connected with the apex of the sternum. The 

 fore-limb has not more than three digits (I., II., and III.), the 

 three metacarpals are fused (except in Archceopteryx), and 



