68 PROFESSOR OWEN ON THE 
Didunculus, and the convexity reigns in the transverse as well as the antero-posterior 
direction ; in Didunculus, however, it is less concave transversely than in Gowra. In 
the breadth or thickness of the interorbital septum Didus resembles Apterya and Palap- 
teryx and shows the same pneumatic cancellous structure. The posterior olfactory 
chambers are partially divided, as in Dinornis, by an upper median septum; each 
compartment, which is 7 lines across and an inch in length, is perforated posteriorly by 
an olfactory foramen more than a line in diameter, from which grooved impressions of 
ramifications of the nerve diverge upon the hind and upper wall of the chamber: ex- 
ternal to the olfactory foramen is a longer one for the passage of a vein into the fore 
and inner part of the orbit. 
The cranial ends of the nasals and nasal process of the premaxillary (Pl. XXIII. 
fig. 1, 22) are flat, depressed, thin plates; the latter at its junction with the frontal is 6 
lines broad, partially divided by a median groove above and a ridge below, and by short 
linear fissures from the nasals: the forward extension of these bones is feebly indicated 
by linear grooves terminating at the outer margins of the nasal branch of the premaxil- 
lary, about 4 inches from its vertical end. The proportion of the base of the upper 
mandible attached to the frontal contributed by the nasals is the same as that indicated 
in the ‘Proc. Zool. Soc.’ 7. ¢. The nasal branch of the premaxillary presents a full 
elliptical transverse section where it quits the maxillary processes, losing both depth 
and breadth as it recedes to join the nasals; here it retains its breadth, viz. 6 lines, but 
continues to be thinned off vertically to the plate above named joining the frontal. The 
under surface of the narrower part of the stem is angular, the upper one being gently 
convex. 
** Where the nasal and maxillary processes diverge, there is a deep groove externally, 
terminating in a canal directed forwards into the rostral part or body of the premaxillary”’. 
This part is subdecurved, pointed, roughened by irregular vascular perforations and 
grooves, with a sharp alveolar border, which describes a sigmoid curve lengthwise, and 
with a deeper concavity of the palatal surface than in Dinornis or Didunculus. Moreover 
the concavity is partially divided lengthwise by a median ridge. ‘The palatal surfaces of 
the maxillary processes and maxillaries are narrow and very convex transversely, inter- 
cepting a long narrow palato-nasal fissure. The outer side of the maxillary process is deep 
vertically and slightly concave lengthwise—a structure not known in Didunculus or any 
Dove, and related, like most other deviations from the Columbine cranial characteristics, 
to the provision of unwonted strength of beak in the Dodo. The maxillary branches 
of the premaxillary have completely coalesced with the maxillaries, as these have with 
the palatines; and the halves of the upper mandible here swell out laterally and more 
so vertically, the maxillaries rising to combine with the outer divisions of the nasals, and 
sending back a short process from their lower and lateral part to join the malar. The 
inner surface of the maxillary process (Pl. XXIII. fig. 1, 22*) is smooth and slightly 
convex vertically ; both upper and lower borders are obtuse and thick. 
Proc. Zool. Soe. 1. c. p. 5. 
