OSTEOLOGY OF BIRDS 



285 



are seven free caudal vertebrae. There are five pairs of dorsal ribs 

 and three pairs of pelvic ribs. 



In Somateria m o 1 1 i s s i ma the first 15 vertebrae of the 

 trunk are without free ribs, the first pair occurring upon the 16th 

 vertebra, and they have good sized unciform processes. The 17th 

 to the 2 1 st vertebrae inclusive are true dorsals, and there are but 

 six free caudals. There are five pairs of dorsal ribs, and three 

 pairs of pelvic ribs, the latter being entirely lacking in unciform 

 appendages. Seven pairs of these ribs have their costal ribs articu- 

 lating with the sternum, while in the case of the last pair of the 

 series the haemapophyses, although long, fail to reach the sternal 

 border. 



Upon examining a specimen of Polysticta stelleri, I 

 find that the first 15 cervicals are without ribs, the first free pair 

 occurring upon the 16th, and they possess unciform processes. 

 17-21 inclusive are true dorsals, and there are seven free caudals. 

 The arrangement of the ribs is the same as found in N e 1 1 a 

 r u f i n a . This latter statement also applies to Oidemia per- 

 spicillata, where we also find that there are 15 cervicals that 

 do not support free ribs, which occur for the first time on the 

 1 6th though they are lacking in unciform processes. Again 17-21 

 are dorsals, with seven free caudals, and the ribs as in N e 1 1 a 

 r u f i n a . 



Although I am not especially considering the vertebral column 

 of the swans in this place, as that will be more fully done further 

 along, yet it may not be altogether uninteresting to compare here 

 the vertebrae and ribs of a typical swan with the corresponding 

 bones of some of the ducks we have been examining, and these 

 comparisons are shown in the subjoined table. 



TABLE 



[Compare with data given in table on page 315] 



SPECIES 



Number of 



vertebrae 



in cervical 



region 



without 



free ribs 



Vertebrae 

 that bear 

 free ribs not 

 reaching 

 sternum 



Dorsal 

 vertebrae 

 (inclusive) 



Vertebrae 

 consolidated 

 with pelvis 



(inclusive) 



Free caudal 

 vertebrae (to 



which py- 



gostyle is to 



be added) 



Olor columbianus. . . 

 Spatula clypeata. . . . 

 Querqueduls discors , 

 Clangula islandica . . . 



23d 1 24th to 28th 29th to 45th 46th to 52d 



2ISt 22d tO 37th 38th tO 44th 



2ISt 22d tO 37th 38th tO 43d 



2ISt 22d tO 37th 38th tO 43d 



6th 17th to 

 16th 17th to 

 16th and 17th 18th to 



Now, in the case of Spatula and Clangula, in the specimens 

 before me, the 38th vertebra, though free and really a caudal, lies 



