356 PROFESSOR OWEN ON THE GENUS DINORNIS. 



outside the fore-part of the palatine, has coalesced with a slender styliform malar, as 

 the fractured surface (26, fig. 1) demonstrates. 



In Didus the palatines arch outwards from their posterior attachments, are broad and 

 smooth mesially, with a sharp crenate edge above ; a thin, outwardly smooth convex 

 ridge is directed outwards and forwards, and a more angular ridge is directed down- 

 wards, and ends in an obtuse point ; a groove divides this from the outer ridge. The 

 upper and outer ridge extends to the maxillary ; the lower ridge subsides before it 

 reaches the maxillary. The palatines form the boundaries of the naso-palatine aperture, 

 and approximate each other at both ends, but do not meet. There is a fossa at the 

 outer part of each palatine, and near the back-part there is a rough concavity ; the 

 rest of the outer surface is convex lengthwise, concave vertically. The boundaries of 

 the maxillary are more readily traceable in Didus than in Dinornis : it forms in Didus a 

 compressed longitudinal plate of bone with thick rounded borders above and below, 

 and almost touches its fellow, leaving a deep narrow chink between the nasal fossa 

 above and the palate below, which is closed by the palatal membrane. 



The middle wall uniting the nasal and palatal plates of the premaxillary in Dinornis 

 terminates by a thick concave border one inch five lines behind the anterior fractured 

 end of the beak, and half an inch in front of the fore-part of the palatal nostril : this is 

 a single long narrow median slit, bifid behind, from the entering vomer, which is above 

 the plane of the palate ; the length of the opening is one inch ten lines ; its breadth at 

 the middle part three lines. The external or facial nostrils are large, probably bounded 

 behind by a slender nasal process ascending obliquely upwards and backwards, as indi- 

 cated by its fractured base developed from the coalesced palatine and maxillary at n', 

 fig. 1 : this process, perhaps, joined the broken part of the lateral process of the nasal 

 at 15. 



The tympanic bone (28, figs. 1 & 3, and figs. 8, 9 & 10, PI. LIII.) presents no fewer than 

 six articular surfaces : two at the upper smallest end (e, e), united by a linear strip of 

 bone, which are convex and adapted to the two glenoid cavities on the under surface of 

 the mastoid : one flat oval surface (/, fig. 9) on the outside below the neck of the con- 

 dyles, for a corresponding surface on the back-part of the mastoid process : one small 

 flat surface {g, fig. 10) on a short process from the inner side of the lower border of the 

 orbital plate, for articulation with the pterygoid : a fifth deep hemispherical pit {h, fig. 9) 

 on the outer border of the lower end of the bone, for the reception of the end of the 

 squamosal, and a large articular surface (i, i, fig. 8) divided by a linear groove into two 

 parts on a remarkably antero-posteriorly extended lower condyle for the joint of the 

 lower jaw : the anterior division of this surface is transversely oblong, convex at its 

 inner half, but concave transversely at its outer half ; the posterior division is slightly 

 convex. The orbital process (k) is a compressed subrhomboidal plate, convex externally, 

 concave and rough for muscular attachment internally ; its base extends from almost 

 the whole anterior part of the shaft of the tympanic. It is broader and not so long as 



