418 MR. ST. GEORGE MIVART ON THE 
postaxial excavation, and which diverge from the hinder part of the neural spine to the 
postzygapophyses. 
This fifth fossa (the median postaxial fossa) shows signs of subdivision at its fundus 
through a slight postaxial projection of the postaxial margin of the root of the neural 
spine. 
The apex of the neural spine is somewhat swollen, and may be much extended antero- 
posteriorly. 
The postzygapophysial surfaces are here, again, somewhat larger, and look much 
more ventrally and less outwards. ‘ 
The twenty-fourth vertebra supports a long nib (the seventh), which articulates by 
its ventral end with the fifth sternal rib. 
Tue TWENTY-FIFTH VERTEBRA. 
This last of the free vertebre differs greatly from any yet described, and considerably 
even from the twenty-fourth vertebra, principally in the diminution of the centrum and 
great augmentation of the neural spine. 
The centrum has its preaxial surface less extended dorso-ventrally, while its ventral 
margin is concave as well as its dorsal one (fig. 55, ac). 
The postaxial surface of the centrum may be different from any thing we have 
hitherto seen; its transverse extent may be nearly three times its dorso-ventral dimen- 
sion. There may be scarcely a trace of dorso-ventral concavity, while the whole surface 
may be but very feebly convex from side to side’; on the other hand, there may be little 
difference between it and the postaxial surface of the twenty-fourth vertebra’. 
The neural canal is even more contracted, especially in its dorso-ventral extent at its 
postaxial end, than in the twenty-fourth vertebra. 
The ventral surface of the centrum presents a quadrangular, subequilateral, much 
flattened surface, such as we have not yet met with; its lateral margins, however, are 
still concave, while its pre- and postaxial margins are respectively rather more concave 
and convex than in the twenty-fourth vertebra. 
The parapophysis is much as in the twenty-fourth vertebra, but extends less outwards. 
The diapophysis is more slender, and projects directly outwards and somewhat 
dorsally ; its distal half, at the least, is rather pre- and postaxially compressed than 
dorso-ventrally depressed. The surface for the tubercle is again less remote from that 
of the head of the rib. 
The prezygapophyses are larger than in the twenty-fourth vertebra, and look more 
dorsad ; the postzygapophysial articular surfaces are still smaller than in the preceding 
vertebra, and look still more ventrad. 
The lateral excavations on the ventral and preaxial sides of the diapophysis have more 
’ As in the specimen 1362. in the College-of-Surgeons Museum. 
* As in the specimen 1317 in the College-of-Surgeons Museum. 
