418 ME. ST. GEOEGE MIVAET 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 neui-al 

 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 rib (the seventh), which articulates by 

 its ventral end with the fifth sternal rib. 



The Twenty-fifth Vertebra. 



This last of the free vertebrae 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 preaocial 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 difiierent 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, subequUateral, 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 'parajiophysis is much as in the twenty-foiu'th vertebra, but extends less outwards. 



The diapophysis is more slender, and projects directly outwards and somewhat 

 dorsally ; its distal hal^ 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 twentj'-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 1362a in the College- of-Surgeons Museum. 

 ^ As in the specimen 1317 in the CoUege-of-Surgeons Museum. 



