425 
of the last centrum (ib. 9, ») extend beyond the hinder expansions of the penultimate 
vertebra. The centrum of the last vertebra contracts to an obtuse point, grooved below. 
The antepenultimate vertebra retains its neural arch, canal, and bifid spine (fig. 38, 7, 2), 
differing only in size and the stunted character of the processes from the antecedent 
free caudals, 
The lower and fore part of the sides of the centrum extend as short, broad, obtuse 
parapophyses. These render the under surface of the centrum transversely concave. A 
similar low obtuse diapophysis projects from the base of the neural arch and con- 
tiguous part of the centrum with which it has coalesced. The gradual diminution of 
the terminal vertebre of the tail to an obtuse point indicates that such an appendage 
was as little indicated by the plumage in Dinornis as in Apteryx. 
In Struthio the transverse processes of the caudal vertebre have assumed, in the third 
of the series (fig. 65, p. 429 of * Mivart’), much of the coalesced characters of the first 
in Dinornis (fig. 36). ‘The antero-posteriorly compressed and transversely extended mass 
representing the neural spine begins to shoot out its upper angles in the third caudal of 
Struthio, and in the sixth (fig. 66, p. 430 of ‘ Mivart’) they more nearly repeat the parial 
divergent spines in Dinornis (fig. 36, ns). In the eighth caudal of Struthio (fig. 67, 
p. 430 of * Mivart.’) a third low spine rises between them. ‘The ninth caudal in Struthio 
(fig. 68, ib.), which is commonly found anchylosed at the neural and hemal borders of 
its postaxial surface with the terminal * ploughshare,’ is the homologue of the foremost 
of the three terminal coalesced caudals in Dinornis (fig. 38,7); but it has lost its 
transverse processes, and a terminally trifid lofty neural arch and spine represent the 
low arch and pair of tuberous neural spines in Dinornis. 
Prof. Mivart ! rightly notices the indications of the two terminal vertebrze which have 
coalesced to form the vertically extended laterally compressed plate of bone, with its 
irregular more or less rounded margin, so markedly distinguishing the termination of 
the vertebral column in Struthio from that in Dinornis. 
The retention of the ploughshare character in the Ostrich relates to the large size of 
the feathers which it supports, and which represent the ‘ rudder-quills’ (‘rectrices’) of 
normal birds of flight. Such caudal plumes, with the similar alar plumes, the better 
developed bones of the unavailable pair of wings and concomitantly developed sternum 
and scapular arch, concur in showing that the great existing flightless bird of Africa has 
receded in a less degree from the volant type than have the extinct wingless birds of 
New Zealand. 
The terminal segments of the ‘axial skeleton’ in Dinornis differ from those in 
Apteryx mainly in the minor modifications of the elements and apophyses constituting 
the palate and beak. As these segments are omitted in Prof. Mivart’s analysis of the 
axial skeleton of the Ostrich, the comparison of the individual vertebre in advance of 
the atlas will not be here entered upon. 
' Loe. cit. p. 431, fig. 69, 
