OCR Text |
Show 1899.] OSTEOLOGY OF THE TUBINARES. 385 Bulweria, Pelecanoides, and the small Petrels, e. g. Oceanites, Procellaria, Cgmodroma. The squamosal prominence (see p. 394) forms the roof and external boundary of the mouth of the temporalis recess, and affords an articular surface for the squamosal head of the quadrate. The paroccipital process (p. 394) is largest in the larger forms ; its outer free border runs upwards and forwards to join the squamosal prominence, forming thereAvith a sharply truncated outstanding process of the skull. Its inner free border can be more or less easily traced running inwards and somewhat forward to the base of the mammillary process of the region representing this. The temporal fossce.-In all the Procellariidas the temporal fossas, when present, take the form of conical depressions, more or less deep, rising obliquely upwards and backwards from the postorbital and squamosal region, which may be taken to form the base of the cone to the sagittal crest in the mid-dorsal line. By means of this fossa the outline of the cerebral and cerebellar regions of the brain are plainly indicated. This is particularly well marked in the case of Priofinus, and scarcely less so in that of some species of CEstrelata and Puffinus. Thus, this region of the skull comes to bear a close resemblance to that of the Penguins. It differs therefrom, however, in the more oblique position of the fossa and the more backward position of the squamoso-parietal wings. In the Diomedeidas the temporal fossas differ conspicuously from those of the Procellariidas, for, instead of taking the form of more or less deep grooves tending to cut off the cerebral from the cerebellar portions of the skull, they are represented only by shallow depressions, of uniform depth, on either side of the parietal region of the skull, and are only discernible by reason of the low ridge representing the periphery of the attachment of the tempo ralis muscle. The trigeminal foramen lies in a more or less deep fossa into which opens the mouth of the temporalis recess : it is situated immediately above the mouth of the large pneumatic aperture already described in the Procellariidas as lying dorsad of the Eustachian grooves. In Diomedea exulans there is a second smaller foramen immediately below the trigeminal, but this is a pneumatic orifice. The orbits in the Procellariidas are only very imperfectly roofed in above. The postorbital process serves to protect the eye from above and behind and the lachrymal in front; the outer border of the nasal gland protects it above. The interorbital septum forming the mesial wall, dividing the two cavities, is perforated. It is bounded antero-internally by the antorbital plate, and postero-internally by the orbito- and alisphenoids. The orbitosphenoid is only very incompletely ossified ; thus in the dried skull the orbit is placed in communication with the brain-cavity. In Cgmodroma, Oceanites, Bulweria, and Pelecanoides the interorbital septum is practically Avanting, being represented only by a slender bar of |