224 



OSTEOLOGY OF AN SERES. 



Of the pelvis and caudal vertebrae. — In order to better illustrate the 

 fact thai the pelvis in the Mergansers is constructed upon the same 

 plan as that hone in other anserine birds, I have contrasted it, in Figs. 

 7 and 8, with the pelvis of the American Eider Duck. It will be seen 

 at a glance that all the characters present in the latter are also to be 

 found in Mergus, simply somewhat modified in concordance with its life 

 as a diver. 



Fig. 5. Left scapula and coracnid. with furcula detached, Mergus serrator ; life size, 

 from specimen 16026, Smithsonian collection. 



By the author. 



The ribs of the first three vertebra? that anchylos in the sacrum 

 have already been described when speaking of these bones in general. 

 Next to them we find that the three succeeding vertebra? throw out 

 their apophyses to the pelvis and firmly anchylos therewith. After 

 them we fall into the deep and oblong pelvic basin possessed by this 

 bird, and the next three vertebra 1 send their processes directly upward. 

 They are followed by a series of eight more that gradually approach the 

 free caudals in form. The anterior one of these has the strongest lat- 

 eral processes, but they are found to abut against the ilia on either side 

 at a point anterior to the middle of the ischiac foramen, and not right 

 behind the cotyloid cavities as in many other birds. The inner margins 

 of the ilia anchylose with the outer ends of these sacro-vertebral apoph- 

 yses, from the acetabula, backward, excepting the last one. 



Opposite the cotyloid cavities we find the enlargement to accommo- 

 date that part of the spinal cord where the sacral plexus is thrown off; 

 the openings for the exit of the latter are double, being placed one 

 above the other. 



Viewing this pelvis of Mergus serrator from above, we always find, 

 jutting out in front, a tuft of bony spicules that form a part of the same 

 system that strap the dorsal vertebra? together. 



The inner margins of the ilia meet and anchylos with the top of the 



