Zoological Society. 57 



there is a deep groove externally terminating in a canal directed 

 forwards into the rostral part or body of the premaxillary ; this part 

 is subincurved, pointed, rough and with irregular vascular perfora- 

 tions, with a sharp inferior border on each side, and a more concave 

 palatal surface than in Dinornis. The long and slender palatines 

 of Dinornis coalesce behind with the vomer and in front with the 

 maxillaries ; they are concave below, particularly at their back part, 

 by the downward extension there of their inner border. 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 downwards, 

 and a more angular ridge is directed downwards with an obtuse apex : 

 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 their 

 ends, but do not meet. There is a fossa at the outer and near the 

 back part of each palatine, where 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 ; but they have coalesced in both, with the pala- 

 tine, malar and lachrymal behind, and with the maxillary process 

 of the premaxillary in front: the maxillary in Didus forms a com- 

 pressed 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, closed by the 

 palatal membrane. 



The tympanic bone of the Dinornis has more a triangular than a 

 quadrate form by reason of the unusually large size of its inferior 

 condyle, which forms its base : the orbital process is a compressed 

 subrhomboidal plate : the lower condyle is not so extended inferiorly 

 in the Bustard (Otis) ; its upper condyle is bifid, as in Dinornis. In 

 Palapteryx it is single, as in Apteryx. In Didus the tympanic bone 

 is subquadrate w r ith the four angles produced, and the upper and 

 hinder one bifurcate, forming the bifid condyle for the mastoid arti- 

 culation : in Dinornis the mastoid condyle is also double, with a 

 linear strip of bone between ; and behind this the pneumatic foramen, 

 where also similar foramina are situated in Didus : in this extinct 

 bird, the orbital process, forming the anterior angle, is compressed 

 and truncate : the outer surface of the bone is smooth and convex 

 vertically ; the inner surface is traversed by a sharp concave ridge 

 extending from the inner division of the upper condyle to the ante- 

 rior part of the inner and lower angle : the anterior division of the 

 inner surface is concave, the posterior one is concave vertically, con- 

 vex transversely. The antero-posterior extent of the condyle for 

 the lower jaw is little, but greatest at its outer part, where it rests 

 upon the shallow reniform outer division of the concave articular 

 part of the lower jaw : the inner, more ridge-like part of the condyle 

 sinks into a deeper transversely extended depression of the same 

 articular concavity. The tympanic of the Dinornis chiefly differs in 



