354 PROFESSOR OWEN ON THE GENUS DINORNIS. 



maxillary (22) as they advance ; meet and coalesce an inch and a half from their con- 

 fluence with the frontals, and terminate in a point at the under surface of the nasal 

 process of the premaxillary (22', fig. 3) two inches and a quarter from the same part, 

 which gives, therefore, the extreme length of the nasal bones: the breadth of their com- 

 mon coalesced base with the intermediate premaxillary is one inch five lines ; that of 

 each nasal is five lines. 



The nasal process of the premaxillary extends over the depressed triangular space at 

 the fore-part of the frontal (22', figs. 2 & 5) ; and the posterior extremities of the nasals 

 (15) have coextended backwards, where a slight linear groove indicates them to have con- 

 verged and almost met behind the premaxillary. The nasal bones in Otis also converge 

 where they overlap the prefrontal (' ethmolde,' Cuv.) in oi'der to join the frontal and 

 include that end of the nasal process of the premaxillary. In Didus the nasals also 

 anchylose with the frontal, where they are separated by the nasal process of the pre- 

 maxillary, as indicated by the two longitudinal fissures, which commencing behind at 

 two lines' distance from the upper border of the anchylosed base of the beak, gain that 

 border at one inch nine lines' distance from the frontal, and thus indicate the proportions 

 of the base of the beak formed by the anchylosed nasals. The fissure can also be 

 traced, as in Dinornis, bending inwards upon the under surface of the nasal process of 

 the premaxillary to about three inches from the frontal, when the fissure returns back 

 inclining to the median line and meets its fellow there. All the outer part of the 

 median stem of the beak of Didus defined by these linear furrows I regard as ' nasals.' 

 The osseous base of the upper mandible of the Dinornis has been separated by fracture 

 of the nasals and premaxillary near this point, and the fractured surface exposes the 

 smooth upper surface of the coalesced prefrontals in the situation in which it appears 

 in the Striithionid(E (14, fig. 5), and which, were the premaxillary to extend as far back- 

 wards as the nasals, would be covered by that bone, as in the Dinornis. 



The nasal process, then, of the premaxillary commencing posteriorly, or terminating 

 by a point where it is partly overlapped by the nasals, quickly expands, and in its turn 

 begins to overlap the converging and contracting anterior ends of the nasals. This 

 reciprocal overlapping must add much to the strength of the bony basis of the upper 

 mandible. The upper surface of the premaxillary, at first flat or slightly concave, soon 

 becomes convex, and gradually broader to the fore-part of the external nostrils, where 

 it bends down on each side to form their anterior boundary, and joins what may be 

 termed the body of the premaxillary (22, fig. 1) .- its breadth at this part is one inch 

 one line, and the transverse curve or convexity of the bone here describes half a circle. 

 From this part forwards the convexity begins to subside, and the bone very gradually 

 contracts as it extends forwards to an inch and a half from the anterior margin of the 

 nostrils ; whence it preserves an equal breadth for the next three-fourths of an inch in 

 advance, where part of the extremity has been broken away : the vertical diameter of 

 the body of the premaxillary regularly decreases to this part ; where, as it is reduced to 



