OSTEOLOGY OF BIRDS 



315 



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

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

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

 longer and nearly straight ceratobranchial elements (f 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 an 

 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 Branta 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 

 a 1 b i f r o n s * 



TABLE SHOWING NUMBER OF VERTEBRAE IN GEESE 



SPECIES 



Branta canadensis 

 Chen hyperborea 



nivalis 



Anser albifrons. . . 



Number of 

 vertebrae 

 in cervical 

 region with- 

 out" free 

 ribs 



Vertebrae 

 that bear 



free ribs not 

 reaching 



the sternum 



i9thand 20th 



19th and 20th 

 19th 



Dorsal 

 vertebrae 

 (inclusive) 



21st to 24th 



21st to 24th 

 20th to 24th 



Vertebrae 

 consolida- 

 ted with the 



pelvis 

 (inclusive) 



25th to 43d 



25th to 41st 

 25th to 41st 



Free caudal 



vertebrae 



(to which 



pygostyle 



is to be 



added) 



44th to 49th 



42d to 47th 

 42d to 47th 



