404 ME. ST. GEORGE MIVAE.T ON THE 



The Thirteenth Vertebra. 



This vertebra slightly exceeds the twelfth in length, but still more in breadth and 

 stoutness. Here, once more, the dorso-ventral extent of the lateral margin of the post- 

 axial surface of the centrum equals the transverse extent of the dorsal margin of that 

 surface. 



The neural arch here attains about its maximum of antero-posterior extent, measured 

 pre- and postaxially in the middle line. 



The median unexcavated part of the neui-al spine is slightly shorter antero-posteriorly 

 than in the twelfth vertebra. 



The free projection of the styliform rib may be for the first time less in extent than 

 in the vertebra next (preaxially) to it ; but it is at the same time thicker. 



The transverse extent of the postaxial part of the neural arch nearly equals that of 

 its preaxial part; and concomitantly with this greater projection outwards of the post- 

 zygapophyses, the lateral margins of the neural laminae (viewed dorsally) become more 

 concave. 



The articular surfaces of both zygapophyses, but especially of the postzygapophyses, 

 are broader in proportion to their length. 



The Fourteenth Vertebra. 



The fourteenth vertebra scarcely exceeds the thirteenth in length, though it does so 

 very decidedly in breadth. Indeed the antero-posterior length of the neural arch in the 

 dorsal middle line is absolutely, though very slightly, less tlian in the thirteenth vertebra. 



The styliform ribs are thicker, the catapophyses more projecting, the zygapophysial 

 articular surfaces broader, while the four margins of the postaxial articular surface of 

 the centrum have become about equal. 



The canal for the vertebral artery has also become rather more capacious. 



The Fifteenth Vertebra. 



With this vertebra the absolute antero-posterior dimension has begun slightly to 

 decrease ; but the transverse development continues to progress. The styliform ribs are 

 still stouter, the zygapophysial surfaces still broader, the neural spine thicker and 

 shorter, and the lateral margins of the neural arch more concave. The postaxial 

 excavation of the neural spine is enlarged into a considerable fossa. 



The metapophysis is rather prominent beneath a prezygapophysis, which may here 

 once again begin to decidedly project, preaxiad, beyond the parapophyses. 



The Sixteenth Vertebra. 



The sixteenth vertebra is, again, like the fifteenth, shorter than its preaxial predecessor ; 



and even the transverse dimension, measured across the postzygapophyses, is scarcely if 



at all greater, though the preaxial part of the vertebra is enlarged transversely, and 



therefore relatively to the more postaxial part as well as absolutely. The posterior end 



