, MR. W. K. PARKER ON THE OSTEOLOGY OF BAL^NICEPS REX. 311 



Mandible. (PI. LXV. figs. 1, 4 & 5.) 

 If the lower jaw of the Balseniceps were the onlj' part of the osteology of this bird in 

 our possession, the same element of the Boat-bill's skeleton would have sufficed for its 

 interpretation. Yet the differences between the larger and the smaller bone are great, 

 exactly answering to the modifications of the pre-maxilla in these two birds. The 

 likeness and dissimilarity of these birds is something similar to that which exists 

 between one of the smaller Antelopes, such as the Gazelle, and one of the massive 

 species, e.g. the Eland. The necessary modifications in the structure of the skeleton 

 required by delicacy on the one hand, and by strength on the other, are well seen in 

 these two very congeneric species. The mandible of the Cancroma is just one degree 

 stronger than that of the Giant Goatsucker (Podargus)— a bird whose relations, Capri- 

 mulgus and Cypselus, have the feeblest mandibles in the whole class, whilst the same 

 bone in Balaeniceps almost rivals the lower jaw of the Hornbills — birds in which this 

 arch has its most massive growth. The pra-maxilla of Balseniceps is less outspread than 

 that of Cancroma : but there is a reason in the structure of the bill in the former bird 

 why the mandible should be still more narrowed ; this is caused by the edge of this bone 

 having to fit exactly in between the marginal and submarginal ridges of the upper jaw. 

 Having been adapted in its anterior portion between these ridges, the rami diverge 

 gently, so as to lie (in a vertical plane) outside the posterior half of the pre-ma.xilla, 

 and also outside the zygoma to its end. Hence the lower jaw of the BalEeniceps is in 

 outline much less like the Magnolia leaf; it is more triangular, and keeps gradually 

 widening for the anterior three-fourths of its length, when it takes a gentle turn inwards 

 for the rest of its extent. In Cancroma the mandible is almost exactly adapted to the 

 pre-maxilla at its edges, just passing within the margin as it approaches the zygoma ; 

 its lower thick part only lying a little outside that arch. This is very much like what 

 takes place in the Goatsuckers, large and small. Moreover the tips of the pre-maxilla 

 and mandible are not notched or emarginate in Cancroma, whilst they are very decidedly 

 so in Balaeniceps, especially in the latter organ. The extent of the confluent symphysis 

 mandibulse is much greater in proportion in the large bird than in the smaller one, as 

 will be seen below, in a tabular comparison of this part in several species of birds. In 

 Cancroma the dentary elements of the mandible (which form more than two-thirds of 

 the rami) are quite distinct from the articular and angular portions, and the angular 

 elements are scarcely confluent with the articular. None of these sutures exist in 

 Bateniceps ; although, from the analogy of its congeners, it must have had all the 

 twelve centres of ossification, in its young state, that are found throughout lite in the 

 Crocodile. This mammalian solidity of the lower jaw is found in but few birds, e. g. 

 the Parrots, Hornbills, and Toucans. The sharpest part of the edge of the mandible 

 in Balaeniceps is the first inch and a half; it then becomes more and more blunt and 

 rounded, until we arive at that thick, rough, elevated posterior end of the dentary which 

 seems to have worn away the margin of the maxilla at its zygomatic end. The 



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