1899.] OSTEOLOGY OF THE TTTBINABES. 389 



division of the hemispheres dorsally. The cerebral fossa is of 

 much greater relative size in the Diomedeidse. 



The olfactory fossce are paired tubular cavities lying immediately 

 in front of the cerebral fossee, and leading out into the olfactory- 

 chamber by a wide aperture. 



The Premaxilla. 



The premaxilla — and, as will be shown presently, the whole 

 facial skeleton — closely resembles that of the Ciconiiformes. 



In the Tubinares it is in all cases more or less produced 

 forwards and strongly hooked at the tip. In breadth it varies. 

 In the Procellariidse, amongst the smaller forms, e. g. Oceanites, 

 what is probably the more primitive form of this region of the 

 skull obtains, in that we can distinguish the three radiating prongs 

 by which the premaxilla is bound to the rest of the jaw, viz., 

 the median, paired, nasal processes and the lateral maxillary pro- 

 cesses. In Oceanites, Cymodroma, &c. these are long and narrow 

 and wide apart. Thus we get a long, median palatal vacuity, and 

 elongated, paired, but horizontal and pervious nares. The nasal 

 processes fuse proximately with the nasal bones and are never 

 more than indistinctly to be made out in this region. The outer 

 border of the maxillary processes in the larger Procellariidae, e. g , 

 Fulmarus, Priofinus — aided by the maxilla— take the form of 

 vertically flattened plates, which in Prion become laterally expanded 

 so as to make the beak boat-shaped — as in Bakeniceps and Can- 

 croma amongst the Ciconiiformes. The great development of 

 these vertical plates causes the narial apertures to look upwards, 

 rather than outwards as is usual. Moreover, it gives the jaw the 

 appearance of great solidity, which attains its climax in the 

 Diomedeidse. 



In all belonging to this subfamily — save the genus Puffinus — 

 as akeady indicated, there is a large vacuity immediately distad 

 of the maxillo-palatine processes and extending forwards to the tip 

 of the jaw. In the genus just referred to as the exception to this 

 rule, the vacuity is represented by a wide chink, not extending 

 forwards further than the middle of the jaw, where the edges of 

 the crevice meet to form a bony roof to this region of the mouth. 

 There is an approach to this condition in Priofinus and Majaqueus. 

 The palatal surface of the maxillary processes attains its maximum 

 breadth in Prion and Pelecanoides. In the Diomedeidae this 

 premaxillary vacuity is reduced to a long narrow chink extending 

 about as far as the middle of the jaw, when, as in Puffinus, the 

 edges meet to form a bony palatal roof. 



The Maxillo-jugal Arch. 



As in the Ciconiiformes, the maxilla, in the adult, is indistinguish- 

 ably fused with the premaxilla. The maxillo-palatine processes, 

 in Oceanites, Cymodroma, and Procellaria, are represented by 

 delicate horizontal, more or less fenestrated, leaf-shaped expansions 

 approaching one another in the middle hne. In the rest of the 



Pboo. Zool. Soc— 1899, No. XXVI. 26 



