PROFESSOR OWEN ON THE GENUS DINORNIS. 355 



different vertebrate classes, the fact did not so weigh with me in considering the serial 

 homology of the vertebral centrums at the base of the skull, and I cannot assign more 

 value to the osteogeny of the basisphenoid in Birds and Lizards than did the embry- 

 ologist Rathke. The ' pituitary floor ' of the ' sella turcica,' which marks the place of 

 the bifurcation of the blastemal capsule of the notochord in the embryo, shows unniis- 

 takeably, in the dissection of the base of the Dinornis skull (PI. LIV. d), the boundary- 

 line between basi- and pre-sphenoid. If I understand Mr. Parker, he regards the 

 bones (s) in Pis. LIII.-LVI., which he calls 'temporal' and 'squamosal,' as standing 

 in neurapophysial relation to his ' basitemporals.' Whether 8 be homologous with 

 Cuvier's 'mastoide' in Reptiles, or with his ' ^caille du temporal' in Mammals, is 

 discussed in my work 'On the Archetype,' &c., 8vo, 1848, pp. 29-42. The only 

 additional argument bearing upon this question is based upon the assertion that the 

 bone 8, in Birds, is not ossified in and from cartilage, but is a 'membrane bone' like 

 the squamosal in Mammals. This assertion does not square with my experience. The 

 ossification of no. 8 in Birds, as in Reptiles and Fishes, begins and ends in the cartilage 

 external to the labyrinth. In adducing other reasons for regarding it as the homologue 

 of Cuvier's 'mastoide' in other Ovipara, I should only repeat what I have elsewhere 

 adduced. But I may here remark that, in the quest of the nature and homologies of 

 the bones in the Bird's cranium, the comparison should be made ascensively from the 

 developmental phenomena and anatomical connexions and relations of the parts in the 

 Cold-blooded Vertebrates, rather than descensively from those in Mammals. 



§ 4. Atlas o/ Dinornis robustus. 



This vertebra consists of the ' hypapophysis' and the ' neurapophyses' in a coalesced 

 state (PI. LIII. figs. 4, 5, 6) : the ' centrum ' articulating with the back part of the base 

 of each neurapophysis, having coalesced with the centrum of the succeeding vertebra, 

 is not here present. The hj'papophysis (ib. hy) is wedge-shaped ; the base is convex 

 transversely, with a medial protuberance from its back part and a smaller one on each 

 side : the anterior surface is excavated and smooth, forming the lower two-thirds of the 

 occipital cup (ib. fig. 4) ; the posterior surface (fig. 5) is plane and roughish for a close 

 attachment to the centrum of the atlas ; the upper margin of the wedge is concave 

 transversely, thick and convex longitudinally. The coalesced bases of the neurapo- 

 physes send each a process inwards, which is concave anteriorly, contributing the 

 upper third of each side of the occipital cup, and resting in part upon the body of the 

 atlas, which occupies their interspace (fig. 4, c). Each neurapophysis then inclines 

 upward and outward, and suddenly expands; it sends a process from its outside 

 downward, which coalesces with the side of the hypapophysis and circumscribes the 

 vertebrarterial foramen (ib. v) ; it sends a larger process backward, with an articular 

 surface (fig. 5, z) on its under and inner part for articulation with the prezygapophysis 

 of the axis-vertebra ; it is convex externally, with a tuberosity on its outer and hinder 



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