THE HIND LIMB IN BIRDS. 



295 



latively short and thick, and the two terminal condyles are 

 large and elongated antero-posteriorly. A prominent ridge, 

 which plays between the proximal ends of the tibia and the 

 fibula is apparent upon the posterior and inferior surface 

 of the outer condyle. A similar ridge is faintly developed 

 in some Lacertilia, and is well marked in the Dinosaurian 

 reptiles. A patella is usually present, but it is sometimes 

 absent, and may be double. Fig. 87. 



The fibula of birds is always im- 

 perfect, ending in a mere style 

 below. Generally it is decidedly 

 shorter than the tibia, but it has 

 the same length as that bone in 

 some Penguins. The tibia, or 

 rather tibio-tarsus, is a highly cha- 

 racteristic bone. Its proximal end 

 is expanded and proditced ante- 

 riorly, into a great cnemial process 

 (which may be variously subdi- 

 vided) as in Dinosauria. The distal 

 end is terminated by a well-marked 

 pulley-like articular surface which 

 is inclined somewhat forwards as 

 well as downwards. Not imfre- 

 quently there is an obliqiie bar of 

 bone on the anterior face, just 

 above the x^uUey, beneath which 

 the long extensor tendons pass. 



The extremity of the cnemial 

 process in Stndhio and Bhea is 

 ossified as an epiphysis; and, in 

 young birds, the whole of the dis. 

 tal articular end of the bone is 

 separated from the rest by a su- 

 tiu'e, and also appears to be an epi- 

 physis. But it is, in fact, as Professor 

 proved, the proximal division of the tarsus (apparently 

 representing only the astragalus of the other Vertebruta), 



A. 



Fig. 87.— The right tibia 

 and fibula of a Fowl. A. 

 front view ; B, external 

 lateral view. T., tibia ; 

 F., fibula ; Cn., cnemial 

 process; Jls., astragalus. 



Gegenbaur has 



