312 PROFESSOR OWEN ON THE GENUS DINORNIS. 



extent of the temporal fossa and the concomitant distance of its boundary from that of 

 the occipital fossa, which might be interpreted as characters of immaturity, are present 

 in the larger, not in the smaller cranium ; and they are associated also in the larger 

 cranium with a development of muscular ridges and impressions which forbid the sup- 

 position that that cranium has belonged to a young individual of the gigantic Dinornis. 

 I conclude therefore that the Dinornis dromioides had relatively larger temporal muscles 

 and a stronger bite than the Din. struthoides. The upper boundaries of the depressions 

 are better defined in Din. dromioides, and there is a vertical ridge marking off the an- 

 terior third of the depression [ib. 6) , like that which may be seen in the cranium of the 

 large Storks and some other birds, but of which there is no trace in the cranium of 

 Din. struthoides. 



The articular surface on the mastoid for the os tympanicum is broader, flatter and 

 shallower anteriorly in Din. dromioides than in Din. struthoides ; and, in both, the lower 

 angle of the mastoid is much less produced below the outer side of the articular cavity 

 than in the Ostrich or Emeu ; but the mastoid process in the Apteryx is much less in 

 comparison with the par-occipital process than it is in the Dinornis. 



The posterior angles of the supra-orbital ridge {ib. 12) are not entire ; but the rugged 

 surface has more the character of a sutural than a fractured one ; and the presence of 

 distinct posterior frontals in a nearly mature skull of an Emeu {Dromaius Nova Hol- 

 landice) {ib. fig. 1, 12, 12) at the same part, leads me to suspect that these parapophysial 

 elements of the frontal vertebra may have remained permanently separate osseous pieces 

 in Dinornis, as in the Reptilia. 



The anterior border of the os frontis shows two deep angular depressions (fig. 5, is) 

 for the articulation of the nasal bones, which are thus proved not to have become anchy- 

 losed to the frontals, as in the Apteryx, Emeu, and most other birds, but to have 

 remained distinct throughout life, as in the Turkey and some other Gallinacea. 



The extent of the supra-orbital ridge is eleven lines, and is, therefore, proportionally 

 much less than in the Emeu or any Struthious bird, except the Apteryx, and apparently 

 also the Dodo : the very slight transverse concavity of the roof of the orbit (fig. 4, 11') 

 and its longitudinal convexity are characters which are intermediate between those of 

 the Apteryx, where the orbital cavity is singularly small and indistinct, and those of the 

 larger existing Struthionidce, and they combine, with the diameter of the optic canals, to 

 show that the eyes of Dinornis were relatively smaller than in the Emeu and Ostrich. 



Part of the inter-frontal suture, usually the last of the proper cranial sutures to dis- 

 appear, may still be seen in the outer table of the skull of the Dinornis dromioides -. there 

 is no trace of it in the skull of the Din. struthoides. 



Tympanic Bone. 

 The third portion of a skull formed part of a small collection of bones of Dinornis from 



