1899.] osxBOLoaY of the tubixakes. 385 



Buliveria, Pelecanoides, atid the small Petrels, e. g. Oceanites, 

 Procellaria, Cymodroma. 



The squamosal prominence (see p. 394) forms the roof and ex- 

 ternal boundary of the mouth of the temporalis recess, and aifords 

 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 therewith 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 mammillaiy process of the region representing this. 



The temporal fossce. — In all the Procellariidae the temporal 

 fossae, 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 Priojinus, and scarcely less so in that 

 of some species of (Estrelaia and Pufiaus. 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 Dioaiedeidse the temporal fossae differ conspicuously from 

 those of the Procellariidao, 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 Procellariidae 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 Procellariidae 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 formino- 

 the mesial wall, dividing the two cavities, is perforated. It is 

 bounded antero-internally by the antorbital plate, and postero- 

 iuternally 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 Cymodroma 

 Oceanites, Btdiveria, and Pelecanoides the interorbital septum is 

 practically wanting, being represented only by a slender bar of 



