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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. LXIII. d), the boundary-
line between basi- and pre-sphenoid. If I understand Mr. Parker, he regards the
bones (s) in Pls. LXII-LXV., 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 'ecaille du temporal" in Mammals, is
discussed in my work 'On the Archetype,' &c., 8 vo, 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. LXII. 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. 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 ; its is convex externally, with a tuberosity on its outer and hinder
Z 2