298 OSTEOLOGY OF TUBINARES AND STEGANOPODES. 



from ilif inferior walls of the lateral canals, but as the carotid canal 

 begins to develop these processes withdraw from the former positions, 



move gradually lower down beneath the centrum, at the same time in- 

 crease in length and importance, so that in those vertebra? where the 

 carotid canal exists they project from its posteroiuferior border directly 

 backward as parallel and not far- separated spines. 



The post-zygapophyses do not appear asdivergeut limbs until we find 

 them so in the eighth vertebra; in all the cervical segments anterior to 

 this one the facets are situate on the inferior aspect of the tuberous 

 hinder end of the neural arch at its lateral angles. 



Metapophyses are seen on the ninth vertebra, but gradually dis- 

 appear, to be entirely absent in the fourteenth or fifteenth. 



The transverse processes in the dorsal region are broad, flat, and 

 horizontal, being directed more and more to the rear as we approach 

 the pelvis. The plates of the neural spines above do not meet each 

 other when the column is articulated, and there is an entire absence of 

 all interlacing, ossified tendons or metapophyses in this region. In 

 fact, all the vertebra} have a very clean-cut, non-angular appearance, 

 with the majority of projecting borders rounded. 



The articular ends of the centra are constructed upon the " hetero- 

 eolous" type; the anterior faces in the ultimate cervicals and leading- 

 dorsals being notably wide and shallow, and often riddled with foramina. 



Pygostyle and the free caudal vertebrae will be spoken of after, the 

 pelvis has been described; in the mean time we will turn our attention 

 for a few moments to the description of the sternum and pectoral arch. 



The sternum (Figs. 29 and 30). — This bone in a Gannet has the most 

 unique form possible. A pectoral aspect of the bone shows that the 

 body has an oblong figure or outline, with the average width nearly 

 equal to half the length. Beyond this parallelogramic part the ante- 

 rior portion projects as a massive- promontory, and a large part of the 

 carina is beyond this again. 



The anterior moiety of the bone is convex on this side, and corre- 

 spondingly concave on the thoracic aspect. Behind, the body is so 

 flattened out as to be nearly horizontal. The costal borders look out- 

 ward and slightly upward, and each possesses six moderately well- 

 developed facets for the costal ribs. There are no pneumatic foramina 

 in the elongated and shallow intervals. 



The principal orifices of this character consist in a diffuse group on 

 the superior aspect of the anterior projecting part, within the general 

 concavity of the bone. 



Either costal process gracefully rises from its base as a laminated 

 and prominent horn, curving in the anterior direction. 



The posterior moieties of the lateral borders are somewhat rounded 

 and extend almost directly backward over the lateral processes behind. 



These postero-external xiphoidal processes are very long and wide, 

 being rounded off at their extremities and directed a little outward. 



