AXIAL SKELETON OF THE OSTEICH. 417 



The twenty-third vertebra supports a long rib (the sixth), which articulates at its 

 ventral end with the fourth sternal rib. 



The 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 vertebi-se, is here decidely smaller. 



The parapojphysis 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 (| natural size). 

 Fig. 53. 



P 

 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, (^). 



The lateral excavation on each preaxial side of the root of the neural 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 lamellae are seen to 

 separate five subequal fossae. 



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 postaxiaUy to the postaxial part of 

 the diapophysis. The two postaxial lateral excavations are separated from the remain- 

 ing median postaxial excavation by the two lamellae which laterally bound the median 



VOL. VIII. — PART VII. March, 1'?>1 4l. ■ 3if 



