1888. ] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 297 



OF THE REMAINDER OF THE SKELETON OF THE TRUNK IN SULA 



BASSANA. 



In this specimen of the common Gannet tbere are twenty-one free 

 vertebra? in the spinal column before we meet the one tbat first anchy- 

 loses to form, with the assistance of the thirteen succeeding ones, a 

 sacrum for the pelvic bones. Then follow eight more free one : devoted 

 to the movable part of the tail. Finally, we have a long pygostyle that 

 probably contains at least six more. 



They are all completely pneumatic save those ulterior free segments 

 in the tail and the pygostyle. The sixteenth and seventeenth vertebra? 

 support each a pair of free ribs; the next four belong to the dorsal 

 series, and all have true vertebral ribs articulating with costal ribs 

 from the sternum. This is also the case with the first two pair that 

 spring from the pelvic sacrum. Behind these there is still another pair 

 of ribs that very much resemble the post-pubic elements in form, whose 

 ha?mapophyses do not reach the costal borders of the sternum. 



In mid-series these ribs support movable epipleural appendages, 

 attached in the usual way to their posterior borders. As I have already 

 stated above, they are completely non-pneumatic. 



The neural canal is notable for being nearly cylindrical throughout 

 the first twenty-one vertebra?; it is only at the region of the enlarge- 

 ment for the brachial plexus that it is rather compressed in the vertical 

 direction. 



The atlas has a minute perforation in its cup, and its neural arch is 

 strikingly broad and deep. Axis vertebra possesses a stumpy neural 

 spine, and its hypapophysis, directed somewhat backward, is very promi- 

 nent. 



The odontoid peg is comparatively small and nearly sessile with the 

 centrum, the latter presenting a concave face below it. 



From the third to the fourteenth vertebra, inclusive, the neural spine 

 is a very inconspicuous character, while from this on it gradually makes 

 its appearance, increasing in size until we have the usually quadrate, 

 longitudinal plate of the dorsal series. 



Third and fourth vertebra? have each a prominent hypapophysis like 

 the one in the axis, but in the fifth this feature nearly entirely disap- 

 pears. 



Sixth vertebra is faintly marked by the carotid canal ; this gradually 

 becomes more and more tubular in the seventh, eighth, and ninth, while 

 in the tenth to the thirteenth, inclusive, it is a closed cylindrical canal 

 of a caliber somewhat less than the neural canal above it. It disap- 

 pears entirely from the fourteenth vertebra. 



The lateral canals extend from the third vertebra to the fifteenth, in- 

 clusive; they are short in any of the segments, and their posterior 

 apertures are far larger than their anterior ones. 



At the commencement of the cervical series the parial parapophyses 

 are short and not particularly well developed. They project backward 



