264 



NEW YORK STATE MUSEUM 



Fig. 6 Right lateral view of the pelvis, cau- 

 dal vertebrae, and sacral ribs of Mergus 

 serrator. Natural size, and drawn by 

 the author from specimen no. 16626, United 

 States National Museum Collection ; same 

 skeleton as figures 1-5 



in Mergus, simply somewhat 

 modified in concordance with 

 its Hfe as a diver. 



The ribs of tlie first three 

 vertebrae that anchylose in 

 the sacrum have ah^eady been 

 described when speaking of 

 these bones in general. Next 

 to them we find that the three 

 succeeding- vertebrae throw 

 out their apophyses . to the 

 pelvis and firmly anchylose 

 therewith. After them we 

 fall into the deep and oblong 

 pelvic basin possessed by this 

 bird, and the next three verte- 

 brae send their processes di- 

 rectly upward. They are fol- 

 lowed by a series of eight 

 more that gradually approach 

 the free caudals in form. 

 The anterior one of these has 

 the slrong-est lateral processes, 

 but they are found to abut 

 against tlie ilia on either side 

 at a point anterior to the mid- 

 dle of the ischiac foramen, 

 and not right behind the coty- 

 loid cavities as in many other 

 birds. The inner margins of 

 tile ilia anchylose with the 

 outer ends of these sacro- 

 vertebral apophyses, from the 

 acetabula, backward, except- 

 ing the last one. 



Opposite the cotyloid cav- 

 ities we find the enlargement 

 to accommodate that part of 

 the spinal cord where the 

 sacral plexus is thrown ofif; 

 the openings for the exit of 

 the latter are double, being 

 placed one above the other. 



