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 unmis- 
takeably, in the dissection of the base of the Dinornis skull (Pl. LIV. d), the boundary- 
line between basi- and pre-sphenoid. If I understand Mr. Parker, he regards the 
bones (8) in Pls. LIJI.—LVI., which he calls ‘temporal’ and ‘squamosal,’ as standing 
in neurapophysial relation to his ‘basitemporals.’ Whether s be homologous with 
Cuvier’s ‘mastoide’ in Reptiles, or with his ‘écaille 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 of Dinornis robustus. 
This vertebra consists of the ‘ hypapophysis’ and the ‘ neurapophyses’ in a coalesced 
state (Pl. 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 hypapophysis (ib. Ay) 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, =) 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 
342 
