318 



TROPICAL WILD LIFE IN BRITISH GUIANA 



the two, wherein tlie ^rowth of one detraets from the (>'rowth 

 of the othei- and definite stages seem to liave been arranged 

 for eaeli to letigthen, so tliat, in the end, one will not far 

 outdistanee the other. 



FEMUK 



In the embryo tlie 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 ])er 

 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 ])one 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. Botli 

 condyles are long and much bent back. 



The embrvonic fibula is longer and rath- 

 er thicker than in the adult. It is 37 



TIBfA 



FIG. 107. 



per cent as long as the libia, while in the ossification of the 



1 1. .1 .• • 1 ^^ . TIBIO-TARSUS OF 



adult tile proportion is only 2.) per cent. the ani 



