OSTEOLOGY OF THE YOUNG OF HOATZIN 601 



spines have developed on any of the vertebrae of the column; 

 and, as a nnatter of fact, their processes are very simple and much 

 reduced (fig. 1). 



The vertebral as well as the sternal ribs are broad and fiat; 

 there are five pairs of the latter, and each pair articulates with the 

 sternum independently, even the two pairs that meet the pelvic 

 ribs, which latter possess epipleural appendages only in the case 

 of the anterior pair. 



In the articulated, cartilaginous skeleton it is not easy to 

 count correctly the number of vertebrae in the column between 

 the last dorsal and first caudal ones. However, I have counted 

 them over several times, and there appear to be fifteen of these; 

 that is, five beneath the anterior part of the ilia and ten posterior 

 to them, which latter can be counted with great certainty. There 

 are six caudal vertebrae and three more in the pygostyle, which 

 makes nine of these segments in the skeleton of the tail. Judg- 

 ing, then, as best I can, there appear to be 44 vertebrae in the 

 spine of Opisthocomus cristatus; but in order to be certain of 

 this, I should like to see the skeleton of a specimen about a 

 month older than either of these. 



When the bird is as old as the one which furnished the skele- 

 ton shown in figure 1 of the present contribution, the ischia of the 

 pelvis exhibit some little advance in ossification; there is also 

 some bone formed in either ilium, in a strip of some width run- 

 ning along the outer moiety of the preacetabular portion, as far 

 back as the middle point over the elliptical ischiadic foramen. 

 The pubic style, which extends far beyond the ischium on either 

 side, has also commenced to ossify along its anterior part. All 

 the posterior parts of these pelvic bones are still in cartilage; 

 and upon the whole, this pelvis possesses much the same appear- 

 ance, in matters of form and development, as it does in the 

 pullet of the common fowl. 



With respect to the shoulder-girdle or pectoral arch, the os 

 furculum is entirely cartilaginous at the stage of development 

 shown in figure 1 ; while a coracoid as well as a scapula have 

 ossified to a very considerable extent, though the extremities 

 of these bones are still in cartilage. A scapula promises to be 

 broad and short as well as considerably curved. 



