OSTEOLOGY OF BIRDS 



315 



length to the first, is peg-shaped, being bluntly pointed behind. 

 As a whole, the thyrohyols curl up slightly at their distal extrem- 

 ities, but this is confined to their cpihrancJual elements, while the 

 longer and nearly straight eeratohrancliial elements (/ and e) are 

 strong subcylindrical rodlets of bone, almost devoid of any 

 curvature. 



TRUNK SKELETON OF THE ANSERINAE 



If we take the spinal column of B r a n t a canadensis as aii 

 example, the vertebrae composing it are seen to be strong and well 

 developed throughout the chain. Apart from their greater size, 

 even when compared with the vertebrae of the largest ducks, they 

 have nevertheless numerous characters enjoyed in common with the 

 vertebral bones as found in those fowls. But they vary in number 

 for the different regions of the spine, when thus compared with 

 the Anatinae, and for the most part, and in agreement with the 

 major portion of the cranium, this division of the skeleton is very 

 thoroughly pneumatic. This does not apply, however, to the free 

 caudal vertebrae and the pygostyle of the wild goose, for those 

 bones are entirely lacking in pneumaticity. I have already given a 

 table [p. 285] comparing the number of vertebrae in the various 

 regions of the spine in several species of ducks. In the subjoined 

 table I have prepared a similar one for the geese. 



From this it will be seen that B r a n t a canadensis has the 

 same number of vertebrae in its spinal column as certain species of 

 Chen and Anser, that is up to the point where the chain begins 

 to be inclosed by the pelvic bones. Through this region it gains 

 two vertebrae, and this gain is retained to the end of the column. 



Chen and Anser agree in the number of vertebrae in their spines, 

 ihe only difference being a slight one due to the ribs on the 20th 

 vertebrae connecting with the sternum in the case of Anser 

 albi f r on s . 



