PEOFESSOE OWEN ON THE GENUS DINOENIS. 181 



The antepenultimate vertebra retains its neural arch, canal, and bifid spine (fig. 38, 7, Ji), 

 difiering 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 vertebrae of the tail to an obtuse point indicates that such an appendage 

 was as little indicated by the plumage in Binornis as in Apteryx. 



In Struthio the transverse processes of the caudal vertebrte have assumed, in the third 

 of the series (fig. 65, p. 429 of ' Mivart '), much of the coalesced characters of the first 

 in Binornis (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 

 Stnithio, and in the sixth (fig. 66, p. 430 of ' Mivart ') they more nearly repeat the parial 

 divergent spines in Binornis (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. 68,1b.), which is commonly found anchylosed at the neural and haemal borders of 

 its postaxial surface with the terminal ' ploughshare,' is the homologue of the foremost 

 of the three terminal coalesced caudals in Binornis (fig. 38, t) ; 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 Binornis. 



Prof Mivart i rightly notices the indications of the two terminal vertebrae 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 Binornis. 



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 Binornis 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 vertebra in advance of 

 the atlas will not be here entered upon. 



The skull of Binornis maximus diflers chiefly in size from that of B. rohustus and 

 B. ingens. It presents the same type of beak and mouth-bones, the same low broad 



' Loc. cit. p. 431, fig. 69. 



2 c 2 



