318 



TROPICAL WILD LIFE IN BRITISH GUIANA 



the two, wherein the growth of one detracts from the growth 

 of the other and definite stages seem to have been arranged 

 for each to lengthen, so that, in the end, one will not far 

 outdistance the other. 



FEMUR 



In the embryo the femur is proportionally much strong- 

 er than in the adult. Its diameter is 18 per cent of its length, 

 whereas in the adult, it is less than 8 per 

 per cent. As the embryo develops, the 

 bone grows thinner, but is large even in 

 the fledgling and for several weeks after 

 the bird leaves the nest. 



TIBIO-TARSUS 



The ossification center of the shaft is, 

 as usual, in the middle of the bone and 

 works out in both directions. The ridges 

 are drawn together at this point and form 

 a kind of narrow waist, which makes it 

 appear as if the bone were composed of 

 two elements grown together. (Fig. 107.) 

 At the upper end the ossification divides 

 on the inner side and forms two points 

 like the points of a writing pen. At the 

 distal end it is greatly expanded with a 

 deep groove on the upper side. This is 

 the groove between the two distal con- 

 dyles and, in the embryo, commences very 

 near the middle of the bone shaft. Both 

 condyles are long and much bent back. 

 The embryonic fibula is longer and rath- 

 er thicker than in the adult. It is 37 

 per cent as long as the tibia, while in the 

 adult the proportion is only 25 per cent. 



TIBIA 



FIG. 107. 



OSSIFICATION OF THE 



TIBIO-TARSUS OF 



THE ANI 



