08 PEOFESSOE OWEN ON THE 



Diduncuhis, and the convexity reigns in the transverse as well as the antero-posterior 

 direction ; in Didunculus, however, it is less concave transversely than in Goura. In 

 the breadth or thickness of the interorbital septum Didus resembles Apteryx and Palap- 

 teryx and shows the same pneumatic cancellous structm-e. The posterior olfactory 

 chambers are partially divided, as in Binornis, 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 (PI. 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' I. c. 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 conca^ity of the palatal surface than in Binornis or Bidunculus. 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, mter- 

 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 Bidunculus 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 (PI. XXIII. fig. 1, 22*) is smooth and slightly 

 convex vertically ; both upper and lower borders are obtuse and thick. 



' Proc. Zool. Soc. I. c. p. 5. 



