| OCR Text |
Show 1899.] OSTEOLOGY OF THE TUBINARES. 383 sagittal crest; in others this crest is very broad. In Procellaria, Pelagodroma, Oceanites, and Gymodroma these fossas can hardly be said to exist. The interorbital region of the frontals is, like the region posteriorly, gently furroAved and moderately Avide. This feature, however, does not obtain throughout the group, but varies according to the form and depth of the supra-orbital grooves on either side. Thus in Procellaria the interorbital region is very broad, relatively broader than in any other Petrel. In this case the supra-orbital grooves look outwards and not upwards as usual, being only narrow and shallow depressions scooped out of the free edge of the frontal. In Cymodroma these grooves are very short antero-posteriorly, their length being less than the widtb across the frontals between the lachrymals. This occurs in no other Petrel. In Oceanites and Pelagodroma the grooves of either side are practically confluent, reducing the interorbital region to a faint and barely perceptible ridge. The grooves are wider posteriorly than in any other forms, crossing the skull almost transversely in this region. In Pelecanoides, Priocella, and Phcebetria the grooves are divided by a high, narrow ridge, which in Priofinus becomes Avide enough to permit the existence of the median groove previously referred to, Avhilst in Pelecanoides it has acquired a knife-like edge. In none of the Procellariidas is there ever any pronounced supra-orbital ledge such as obtains in the Penguins. In some, as in Priocella, this is feebly developed, but it is never conspicuous. In the Diomedeidae the case is otherwise. In this group, and especially in Diomedea exulans, it may be as well developed as iu Catarrhactes amongst the Penguins, and, as in this genus and that of Pygoscelis, the free edge of this ledge is greatly flattened. The Base of the Skull.-The typical Procellarian form of the basitemporal plate of the parasphenoid is triangular, with a free anterior border. From this it follows that the Eustachian passages are represented by grooves intead of tubes. In Procellaria, Oceanites, Cymodroma, Pelagodroma, Bulweria (occasionally), PuMnus (P. Jcuhli), and Pelecanoides a tube is more or less perfectly formed, by the downgrowth of a thin plate of bone from the alisphenoidal wings of the parasphenoid. In all the Procel-lariicte except Pelecanoides there is a more or less conspicuous aperture, receiving numerous pneumatic foramina, opening downwards immediately above the pneumatic grooves, to the inner side and a little in front of the articular surface of the quadrate. This aperture is in some cases of very considerable size, e. g. Fulmarus alacialis: a probe passed doAvn it, in a forward direction, leads into the parasphenoidal rostrum. In the Diomedeidae this aperture is smaller and opens directly backwards rather than downwards ; furthermore, it is situated much nearer the middle line than in the Procellariidas, inasmuch as it does not pass the le\*el of a line drawn through the mammillary processes, whilst in the latter, as just stated, it opens near the quadrate articular surface. In |
