398 MU. w. p. PTCRAFT ON THE [Mar. 21, 



V. The Eibs. 



The cervical ribs are styloid, and in the middle region of the 

 neck are often of considerable length, e. g. PeJdf/odroma, Puffiniis 

 assimilis. They become very short postei'iorlj', and finally — on 

 the 3 or 4 vertebrse preceding the thoracic — free. Anteriorly 

 they fuse, above, with a process from below the anterior zyga- 

 pophysis (diapophysis), below with a ventral lamella running 

 out\\ards and forwards from the centrum (parapophysis). Thus a 

 canal is formed through which the carotid passes. More or less 

 well-marked catapophyses occur from the 6th to 10th vertebrse. 

 There are 7 pairs of thoracic ribs, all of which, save the last, 

 articulate by means of sternal segments with the sternum. The 

 sternal ribs of the 7th pair are attached by ligament to the 

 posterior border of those next in front. In Pelecanoides the 

 thoracic and sternal ribs increase greatly in length from before 

 backwiirds so as to recall those of tlie Alcidae. In Pelecanoides and 

 Diomedea only are two pairs of thoracic ribs overlapped by the 

 ilium. 



Uncinates are present in all but the last one or two pairs. In 

 Pelecanoides they are placed in the same horizontal plane and 

 about halfway down the shaft. In all other cases they are seated 

 anterioz'ly low down, near the distal g of the rib and rise backwards 

 to about its middle. They are moderately long and slope 

 obliquely upwards. In all cases they project beyond the rib next 

 behind, and often extend to that succeeding this. 



A very useful table showing the number of the vertebrae, ribs, 

 and uncinate processes in the different genera is given in Forbes's 

 memoir (6). 



vi. The Steexum and Pectoeal Giedle. 



The sternum assumes two forms— (1) that in which the posterior 

 border is notched, and (2) that in which it is entire. The first 

 includes all the genera except Pelecanoides, and the small forms 

 included under sections A and B of the Procellariidse — a. g., 

 Procellaria, Oceanifes. "When the posterior border is notched, the 

 anterior coracoid border is produced forwards far beyond the level 

 of the anterior lateral processes. When the posterior border is 

 entire, the anterior, coracoid border does not project far forwards. 

 Pelecanoides belongs to this last division, but can at once be 

 distinguished from the rest by reason of its great length in 

 proportion to its width, in the feeble development of the sjpincc 

 externa, and in that the articular surfaces of the sternal ribs are 

 confined to the free edge of the anterior lateral process. In 

 Oceanites and Pelagodroma there is a large fenestra in the anterior 

 dorsal region of the carina. As will be seen by the appended Key, 

 the various genera which have a notched sternum can only very 

 imperfectly be distinguished one from another. 



Pneumatic foramina opening on to the dorsal aspect of the 

 sternum occur in Majaquevs, Priofinus, Ossifraga, and Diomedea. 



