AXIAL SKELETON OF THE STRUTHIONID 2. 39 
THE SACRAL VERTEBRZ. 
The three sacral (the thirty-third, thirty-fourth, and thirty-fifth) vertebre are, in 
Apteryx, very distinct from both their preaxial predecessors and their postaxial suc- 
cessors. Each sends out on each side a transverse process to abut against the post- 
acetabular part of the ilium. 
THE SACRO-CAUDAL VERTEBR. 
The vertebre of this category are fewer in number in Apteryx than in any other of 
the Struthionid, and are singularly compressed laterally. They are devoid of trans- 
verse processes, and are chiefly remarkable for the peculiarity of their position. Instead 
of ascending, as in Rhea, these vertebree descend ventrad to the postaxial parts of the 
ilia. In spite of these, they are less ventrally extended between the acetabula than in 
any except Rhea; so that when the pelvis is held horizontally with one of the acetabula 
opposite the eye, about half the aperture of the acetabulum of the opposite side becomes 
visible. The nearest approximation to this condition is that found in Caswarius, though 
considerably less of the opposite acetabulum can thus be seen in that genus. 
THE CAUDAL VERTEBR. 
These vertebra are from seven to nine in number—namely, seven in A. australis and 
nine in A. owenii. Transverse processes are present in the third, fourth, and fifth 
caudal vertebre, especially in the two latter; and these help to produce a broadening- 
out of -the fourth and fifth or the fourth, fifth, and sixth caudal vertebre; so that the 
skeleton of the tail is wider towards its middle than it is either more pre- or more 
postaxially. This is a character not similarly marked in any other genus of the 
Struthionidee. 
The pygostyle is rather elongated, conical, irregular, and somewhat laterally com- 
pressed and flattened ventrally. It looks like three or four successively smaller and 
smaller vertebre ankylosed together. 
THE PELVIS. 
_ When viewed preavially the pelvis is remarkable for the much greater divergence of 
the ilia, which form together a much more obtuse angle than in any other of the 
Struthionide. It is also remarkable for the much greater visibility of the ischia and 
pubes (owing to their extreme descent postaxially), and for the relatively much longer 
last rib. 
Viewed postaaially the same peculiarities are noticeable, as also the postaxial descent 
of the ilia (which is much as in Caswarius), and the absence of supratrochanteric 
processes. ‘The ilia are very much flattened against the postacetabular vertebre 
included between them. 
Viewed laterally, the slenderness of the pubis and breadth of the ischium are remark- 
