178 GENERAL ORNITHOLOGY part ii 



bird, which is digitigrade, that is, walks on its toes with its heels in 

 the air, as it is of a man, who is plantigrade, that is, walks on the 

 whole sole of the foot, with the heel down to the ground. In a 

 carver's language, the thigh is the " second joint " (from below) ; 

 the leg is the " drumstick " ; the rest of a fowl's hind limb does not 

 usually come to table, having no flesh upon it. 



Before proceeding to the next segment of the limb, I must dwell 

 upon the ankle-joint, situated at the heel, — the point C, — corre- 

 sponding to the carpal angle or bend of the wing, G, in Fig. 27. 

 There we found, in adult birds, two small carpal bones, or bones of 

 the wrist proper ; and noted the presence in the embryo of several 

 other carpals (Fig. 29), which early fuse with the metacarpus. Just 

 so in the ankle, there are in embryonic life several tarsal bones, or 

 bones of the tarsus (Lat. tarsus, the ankle) ; all of which, however, 

 soon disappear, so that there appears to be no tarsus, or collection 

 of little bones between the tibia and the next segment of the limb, 

 the metatarsus. An upper tarsal bone, or series of tarsal bones, fuses 

 with the lower end of the tibia, making this leg-bone really a tiUo- 

 tarsus ; and similarly, a lower bone or set of bones fuses with the 

 upper end of the metatarsus, making this bone a tarso-metatarsus. 

 So there are left no free bones in the ankle-joint, which thus appears 

 to be immediately between the leg-bone and the principal foot-bone ; 

 but which is nevertheless really between two series of tarsal bones, 

 the separateness or identity of which has been lost.^ 



The next segment of the limb, C to D, or the foot proper, is 

 represented by the principal metatarsal bone, mt. This corresponds 

 to the human instep or arch of the foot, nearly from the ankle-joint 

 quite to the roots of the toes. The metatarsal bone, like the meta- 

 carpal of the hand, which it represents in the foot, is a compound 



^ The exact homologues of a bird's vanishing tarsal hones are still questioned, 

 Gegenbanr showed the so-called epiphysis or shoe of hone at the foot of the tihia, 

 and the similar cap of bone on the head of the principal metatarsal bone, to be true 

 tarsal elements. Morse went further, showing the tibial epiphysis, or upper tarsal 

 bone of Gegenbanr, to be really two bones, which he held to correspond with the 

 tibiale and flbulare, or astragahis and calcaneum of mammals ; these subsequently 

 combining to form the single upper tarsal bone of Gegenbaur, and finally becoming 

 anchylosed with the tibia to form the bitrochlear condylar surface so character- 

 istic of the tibia of Aves. The distal tarsal ossicle he believed to he the 

 centraU of reptiles. "Wyman discovered the so-called " process of the astragalus " to 

 have a distinct ossification, and Morse interpreted it as the intermedium of reptiles. 

 Later views, however, as of Huxley and Parker, limit the tibial epiphysis to the 

 astragalus alone of mammals. If these opinions be correct, other tarsal elements 

 (more than one) are to be looked for in the epiphysis of the metatarsus. Whatever 

 the final determination of these obscure points may be, it is certain that, as said in 

 the text above, the lower end of a bird's tibia and the upper end of a bird's meta- 

 tarsus include true tarsal elements, just as the upper end of the metacarpus includes 

 carpal elements ; and that a bird's ankle-joint is not tibio-tarsal or between leg-bone 

 and foot-bones, as in mammals, but between proximal and distal series of tarsal bones, 

 and therefore medio-tsxs&l, as in reptiles. 



