314 MR. W. K. PARKER ON THE OSTEOLOGY OF BAL^NICEPS REX. 



Entire Ramus. Dentary. 



in. lines. in. lines. 



Caprimulffus europeeus 1 6 10| 



Podargus humeralis 2 8 110 



Cancroma cochlearia 4 8 3 6 



Baleeniceps rex 8 6 7 



Ardea cinerea b' 3 4 6 



Ciconia argala 15 4 13 



Bticeros bicornis 11 8 10 



Macrocercus ararauna 2 6 1 2 



Calyptorfiynchua naso 2 4 1 2 



Diomedea exulans 9 6 7 



PlaiaJea Uucorodia 8 7 3 



Peleeanus onocrotalus 17 9 6 9 



Here it will be seen that the relative length of the dentary is, as a rule in birds with 

 long bills, in direct proportion to the strength of the jaw, and that the Little Goat- 

 sucker has in this respect the advantage of the Pelican ; for both the dentary bone 

 and the symphysis are larger in relation to the rest of the jaw in the little bird than in 

 the great one. In Caprimulgus the dentary reaches more than halfway towards the 

 end of the ramus, whilst in the Pelican it reaches very little above one-third. In 

 Buceros bicornis five-sixths of the jaw is dentary, and in Balmniceps it bears the pro- 

 portion of seven to eight and a half. In the Parrot tribe, the unique state of curvature 

 of the upper jaw, which passes down in front of the mandible, causes that organ, 

 especially the dentary part, to be short ; but here what is lost in length is gained in 

 depth, and the jaws of these birds are amongst the strongest in the class. The 

 number of ossific centres in the mandible of birds can be seen only in young spe- 

 cimens, although a great proportion of the class retain parts of the sutural lines — the 

 bones at these places being thin and elastic. But we have seen that whilst complete 

 coalescence of these parts is the rule in such families as the Parrots, the Hornbills, and 

 the Toucans, yet the Balseniceps is very peculiar, in its own group, in possessing this 

 structure. 



Professor Owen does not mention the existence of the ' coronoid ' bone in the man- 

 dible of the young Ostrich ; nor have we seen it in that bird, nor in the young Emeu. 

 The same may be said of Owls, Pigeons, Gallinaceous birds, and the Crow tribe. In a 

 very beautiful skeleton, however, of the Australian Jabiru, Mycteria australis, at the 

 British Museum', this piece has a very similar size and form to that of the Crocodile, 

 and is quite distinct, although coalescence has taken place to a very considerable extent 

 in the other elements of tiie mandible. 



In the Boat-bill it appears to have been large, but coalescence has defaced all but its 

 anterior boundary, although probably it was distinct in the young bird ; and as that 

 part of the jaw is extremely well developed in the Balseniceps, — most likely iu it too. 



In the Heron it is large, and can still be traced even at the posterior part of its upper 



' Prepared by Mr. E. Gerrard. 



