PROFESSOR OWEN ON THE GENUS DINORNIS. 65 



of the prosencephalic one {p), and sinking mucli below it; the mesencephaUc fossa (o) 

 is comparatively small. 



The transverse section across the broadest part of the cranium shows that the pros- 

 encephalic cavity is far from being of corresponding breadth : a considerable extent 

 of diploe intervenes between that chamber and the base of the postfrontal processes. 

 The outer and inner tables unite without diploe above the highest part of the upper 

 longitudinal elevations of the cerebrum. The inner circumference of the olfactory 

 orifices is partially grooved. 



In order to gain some idea of the size of the bird to which the largest cranium 



belongs, I have compared the diameter of its foramen magnum with that of a lower 



cervical vertebra and of a middle dorsal vertebra, both referable by their size to the 



Dinornis giganteus, the same comparisons having previously been made in the skeleton 



of the Ostrich. 



Dinornis. Ostrich. 



Lines. Lines. 



Transverse diameter of the foramen magnum 9 6^ 



Transverse diameter of middle of spinal canal, lower cervical vertebra . G^ .5 



Transverse diameter of middle of spinal canal, dorsal vertebra .... 7 4^ 



From the above admeasurements and comparison we might be led to conclude that 

 the skull of the Dinornis yielding that of the foramen magnum belonged to a larger 

 species than the vertebrae ; but the size of these vertebrae forbids the supposition ; for 

 they are larger in proportion to the size of the skull compared, than in the Ostrich. 

 The canal for the spinal chord is, in fact, singularly small in proportion to the bulk of 

 the entire vertebra in Dinornis as compared with that in the Ostrich or other birds, 

 and forms, as I have pointed out in a former Memoir, one of the peculiarities of the 

 large wingless birds of New Zealand. The cervical vertebra, for example, with a spinal 

 canal six and a half lines wide, has a body of four inches in length ; whilst that of the 

 Ostrich with a spinal canal five lines in diameter has a body only two and a quarter 

 inches in length ; and the dorsal vertebra presents similar relations. 



Lower jaw.- — An almost entire lower jaw of a Dinornis or Palapteryx, of rather smaller 

 size than the one of which a large portion is figured in vol. iii. pi. 54. figs. 6, 7, closely 

 accords with that portion as far as they can be compared : the symphysial end of the 

 jaw is rounded and short, and impressed below by two parallel longitudinal grooves, sg. 

 Each ramus is slightly bent in a sigmoid flexure, concave below at the anterior half, con- 

 vex at the posterior one. The alveolar border is pierced by vascular grooves and fora- 

 mina at its anterior part, and obliquely levelled off to an edge behind. There is on 

 coronoid process, and no vacuity in the ramus of the jaw, but only a deep longitudinal 

 groove half an inch long, between the originally distinct 'angular' and 'surangular' 

 pieces, which groove is completely closed up on the inner side by the splenial piece : 

 in this respect the present lower jaw diifers from that portion of a very large one 

 ascribed to the Dinornis in my former Memoir, vol. iii. pi. 53. figs. 1 & 2. . 



