33 2 



NEW YORK STATE MUSEUM 



in another table [p. 315] we find that Branta canadensis 

 has 49 vertebrae in its column, while O 1 o r columbianus has 

 52, a gain of three vertebrae for the swan. This gain is made in 

 the upper cervical region, and probably the three vertebrae follow- 

 ing next after the axis. Two of them, at least, may be found here, 

 and perhaps the other a little further down the chain ; or even one 

 of the true dorsals, as but four of these support true vertebral ribs 

 in the goose to five in the swan. 



The vertebrae of this column in Olor, omitting those of the tail, 

 are all highly pneumatic, and possess much the same character as 

 they do in the spinal column of Branta canadensis. The 

 four last dorsals in Olor, however, possess well developed, quadri- 

 form haemal spines, that are but rudimentary in Branta. The 

 centra of these bones are also more laterally compressed in this 

 region, in the swan than they are in the goose. The skeleton of 

 the tail in the former is well developed, and terminates with a 

 large py go style [see pi. 2]. A pair of long, free ribs, without 

 unciform processes are supported by the 23d vertebra of the column, 

 while there are five pairs of dorsal ribs, all having unciform ap- 

 pendages, and all connecting with the sternum by costal ribs. The 

 latter are all highly pneumatic while the thoracic ribs are not so. 

 None of the four pairs of pelvic ribs have epipleural processes, but 

 they are connected with the sternum through costal ribs, the an- 

 terior pair of which latter are only pneumatic. In addition to this 

 long series, there still exists, behind the last pair of pelvic ribs, a 

 true pair of " floating vertebral ribs," that connect below with a 

 pair of costal ribs that fail by several centimeters to reach the 

 sternum ; their sternal ends simply articulating with the hinder 

 border of either ultimate costal pleurapophysis at about its middle 

 point. When all are articulated in situ, this series of ribs, pro- 

 gressively sweeping back as they do, reminds one of the arrange- 

 ment of these parts in some of the loons, a resemblance that by 

 no means appears any the less striking when we take in consid- 

 eration therewith, the long, narrow pelvis of this swan, as well 

 as some of the characters of its sternum. 



Apart from the matter of size, and some change in relative form, 

 the character of the pelvis of Olor columbianus agrees es- 

 sentially and closely with the pelvis of Branta canadensis. 

 On the dorsal aspect, however, in the postacetabular region, it is 

 seen that the parial interdiapophysial foramina are almost entirely 

 sealed over with bone in the swan, while in the goose they are 

 more or less patulous. Again the distal free extremities of the 



