OSTEOLOGY OF BIRDS 32Q 



they extend to some degree above the articular summit of the bone. 

 The entocnemial crest is the more prominent of the two; its free 

 border being sharp. On the other hand, the ectocnemial apophysis 

 is thickened, and is found in the transverse plane. It descends a 

 little lower on the shaft, but is less lofty in proportion. A fibular 

 ridge of 3.5 centimeters in length develops on the side of the shaft 

 for articulation with the smaller bone of the leg. Distally, the 

 condyles of the tibiotarsus are of good size. They stand in parallel 

 planes, and pretty well apart; the whole distal end of the bone 

 having a pronounced oblique curvature inward. 



An anterolongitudinal groove marks the lower fourth of the 

 shaft ; it being transversely spanned below by a strong osseous 

 bridge, seen in so many birds. 



With a transversely flattened head, the fibula in B r a n t a 

 canadensis becomes greatly reduced in size below its articula- 

 tion with the tibiotarsus. At about the junction of the middle and 

 lower thirds of the shaft of the latter, the two bones fuse together, 

 while below this point all the distal moiety of the fibula is plainly 

 discernable, even including its enlarged distal end. This last has 

 an anterolateral position, and is situated opposite the bony bridge 

 that spans the tendinal channel in front. 



The characters of these leg bones as here given for Branta are 

 essentially repeated in Anser albifrons and Chen h . 

 nivalis ; the former having a tibiotarsus of 12.6 centi- 

 meters in length, and the latter one of 15 centimeters. 



In Dendrocygna autumnal is this entocnemial crest of 

 the tibiotarsus is very sharp and thin, while the bone has a length 

 of about 10 centimeters. In Branta canadensis the tarso- 

 metatarsus has a straight' shaft, with its faces more or less flattened; 

 its anterior aspect being the most so. Its extremities are mas- 

 sively developed ; the " hypotarsus " being bulky though not ex- 

 tending far down upon the shaft, and being somewhat compressed 

 in the anteroposterior direction. Four low vertical graduated 

 ridges give rise to three longitudinal grooves upon its posterior 

 aspect for tendons. There is also one long perforation, just next 

 to the internal side of the process, which at the same time is the 

 longest. This form of the hypotarsus agrees with what we see 

 in Anser and Chen, while in Dendrocygna the internal groove 

 comes near being closed over by a lapping of the sides below. 



The upper part of the groove upon the anterior aspect of the 

 shaft of the tarsometatarsus in Branta is deep; the anteroposterior 



