Prof. T. H. Huxley on a new Specimen of Glj'ptodon. 127 



comparatively thia bony plate, so curved as to form a segment of a 

 hollow cylinder of much larger diameter in the front than in the 

 hinder vertebrce, the sides of which pass superiorly into the arches of 

 the vertebrae. 



The foremost vertebra of the thirteen is as broad as the posterior 

 part of the ' trivertebral bone,' and presents a couple of convex arti- 

 cular facets which articulate with the lateral articular concavities 

 described above in that bone. The vertebrae rapidly narrow, how- 

 ever, until the fourth is not more than three-fifths as wide as the 

 first, while it is proportionately deeper ; and this increase of depth 

 relatively to width goes on until in the thirteenth vertebra the spinal 

 canal is deeper than it is wide. 



The spinous processes of these vertebrae are all broken short off ; 

 but sufficient remains of their bases to make the following points 

 clear. 



The spinous process of the first is almost obsolete, being a mere 

 ridge sloping back towards the second, with which it is continuous. 

 This appears to have been necessary to afford the requisite play for 

 the knob of the trivertebral bone in its movements of flexion and ex- 

 tension on the rest of the spinal column. 



The spinous process of the second vertebra was long and thick, 

 and probably somewhat high. It appears to have been completely 

 distinct from the third, which was thinner, and was anchylosed with 

 its successors (as far as that of the twelfth vertebra inclusive) into a 

 long continuous crest. The apices of the spinous processes may, 

 however, have been distinct. So much as is left of the base of this 

 crest shows that it was thickest at the sixth and seventh vertebrae (of 

 the thirteen), and that it became thinner both anteriorly and pos- 

 teriorly. 



The' spinous process of the twelfth vertebra, forming the termina- 

 tion of the crest, appears to have ended in a free, thin, but rounded 

 edge. What remains of the spinous process of the thirteenth ver- 

 tebra, on the other hand, thins off anteriorly to a natural edge, which 

 is inclined upwards and backwards. Posteriorly the spinous process 

 becomes very thick and stout, and appears to have had a considerable 

 height. It ends in a fractured hinder margin. 



The broad wing-like plates which represent the coalesced trans- , 

 verse processes of the first, second, and third vertebra? of the thirteen, 

 exhibit distinct articular surfaces lor the capitula and tubercula of 

 ribs. Further back, the natural edges of the apophysial ridges 

 are broken away, up to the eighth vertebra. Here they are entire on 

 the left side and broken on the right ; but, curiously enough, the 

 broken processes are higher than the entire ones, so that the transverse 

 processes in this region of the body must have been asymmetrically 

 developed. The thirteenth vertebra presents peculiarities which 

 could only be made intelligible by a lengthened description, and by 

 figures. The contours of the articular processes become first di- 

 stinctly traceable at the posterior part of the eleventh vertebra. They 

 Are better marked at the posterior part of the twelfth, and at the an- 

 terior part of the thirteenth vertebra. 



