AXIAL SKELETON OF THE OSTRICH. 417 
The twenty-third vertebra supports a long rib (the sixth), which articulates at its 
ventral end with the fourth sternal rib. 
Tue TWENTY-FOURTH VERTEBRA. 
The twenty-fourth vertebra differs from the twenty-third principally in the much 
greater length (dorsally) of the neural spine. 
The centrum has its postaxial surface more concave dorso-ventrally, as also is its 
ventral margin, which at the same time is more everted postaxially. 
The ventral surface is slightly flatter. The neural canal, which has been diminishing 
in the last few vertebree, is here decidely smaller. 
The parapophysis is much as in the twenty-third vertebra. 
The diapophysis is somewhat less produced preaxially; and its distal end is more 
THE TWENTY-FOURTH VERTEBRA (3 natural size). 
Fig. 53. 
Lateral aspect. Letters as before. 
rounded. The surface for the tubercle is again less remote from that for the head 
of the rib (fig. 53, d). 
The lateral excavation on each preaxial side of the root of the newral spine is still larger, 
and separated only by a vertical lamella of bone from the postaxial lateral excavation, 
which is here greatly augmented in size. 
Thus, when the neural arch is viewed dorsally, five radiating lamelle are seen to 
separate five subequal fosse. 
The two preaxial lateral excavations are separated by the preaxial part of the root of 
the neural spine. The two postaxial lateral excavations are each separated from the 
adjacent preaxial lateral excavation by a vertical lamella of bone running from the 
middle of the side of the neural spine outwards and postaxially to the postaxial part of 
the diapophysis. The two postaxial lateral excavations are separated from the remain- 
ing median postaxial excavation by the two lamelle which laterally bound the median 
VOL. VIlI.—PART vil. March, 1874. . 3N 
