OSTEOLOGY OF THE YOUNG OF HOATZIN 603 



though the tendon in which it should occur is thick and broad. 

 The tibiotarsusis bulky and thick, being much enlarged at its 

 extremity — the distal, cartilaginous condylar portion being con- 

 spicuously extensive. 



Very early in the development in the chick the three tarsal 

 bones, which eventually fuse to form the tarsometatarsus, unite 

 at the juncture of the middle and lower thirds of the shaft, the 

 fusion being still further advanced in the pullet (fig. 1). 



One of the most striking characters in the skeleton of the 

 young Opisthocomus is the enormous size of the feet, as com- 

 pared with the remaining proportions of the bird itself. This 

 feature is, of course, by no means lost in the fowl as we find it 

 in nature; but then the discrepancy does not seem to be so great 

 on account of the presence of the plumage, which lends the 

 appearance of greater bulk to the body. (Compare figs. 1 and 

 2 with 4 and 7.) 



The phalanges are stout and relatively long; the ungual joints 

 large and strong, and to some extent curved, especially the claw 

 of the hallux. As in so many birds, the arrangement of the 

 jomts of the pedal digits is 2, 3, 4, to first, second, third, and 

 fourth toes, respectively. 



Transversely attached to the posterior border of the smnmit 

 of the tarsometatarsus, just anterior to the short, single-grooved, 

 cartilaginous hypotarsus, there is a tough, curved piece of car- 

 tilage which, in life, fits closely in between the condyles of the 

 tibiotarsus. It appears as though it might, to some little extent, 

 ossify later in life, as it does in certain gallinaceous birds — a 

 group to which the hoatzin is, in a way, related, as its mor- 

 phology seems to indicate. This piece of cartilage is of some 

 considerable size even in the chick or nestling. 



At the nestling stage, the integuments of this species are thick 

 and tough, and these characters seem to be, to some extent, en- 

 hanced as the bird grows, for I find them to be still thicker and 

 tougher in the pullet. 



Figures 3 to 8, inclusive, give several of the characters of the 

 superficial anatomy of the young of the hoatzin at the two stages 

 of its existence here being considered. These show the reticula- 



