138 BRITISH FOSSIL REPTILES. 



In the fifth caudal the outer prong is again shorter, and in the sixth it is a mere 

 tubercle ; at this part of the tail the hypapophyses begin to lengthen, bifurcate, and 

 progi'essively increase in length to the sixteenth caudal, and thence gradually diminish 

 and subside ; yet the general configuration of the neural arch, the contour and degree 

 of production of its posterior border, and the shape of the zygosphene, remain almost 

 unaltered throughout. 



In a true Boa constrictor, with 305 vertebrae, 71 at the anterior part of the trunk have 

 long hypapophyses ; and of the 60 caudal vertebrse, 44 have bifid hypapophyses. The 

 first caudal is characterised by the sudden shortening of its ribs, and by a short 

 process from the middle of their outer surface : this process is longer and nearer the 

 head in the next rib ; and in the third caudal vertebra the rib seems to bifurcate from 

 its proximal end, which has become anchylosed to the diapophysis. Beyond the eighth 

 caudal the outer costal prong or process disappears, and the anchylosed rib represents 

 a long deflected diapophysis to within three or four vertebrae from the end of the tail. 

 The last imperforate obtuse bone of the tail is obviously a coalescence of three vertebrae. 



In the Rattlesnake {Crotalus, PI. 2, figs. 9-12) the hypapophyses {h) continue to 

 be developed singly, and of equal length with the neural spines (;«■), throughout the 

 trunk; and any single vertebra might be distinguished from an anterior trunk- 

 vertebra of a JBoa or Fython by the following characters : the diapophysis {d) developes 

 a small, circumscribed, articular tubercle from its upper convexity, and a short process 

 (f/') from its under part, extending downwards and forwards below the level of the 

 centrum (c) ; the anterior zygapophysis (z) seems to be supported by a similar process 

 [d") from the upper end of the diapophysis, the point of which projects a little beyond 

 the end of the zygapophysis (fig. 1 0) ; the zygapophyses are less produced outwards 

 than in the Python; the zygantra {za, fig. 11) are more distinct excavations. 



In the Cobra di Capello {Naja, PI, 2, figs. 13-16), the diapophysis presents the 

 same well-marked tubercle {d) upon its upper part, but its lower end {d') is much less 

 produced than in the Rattlesnake; the process of bone {d") underpropping the 

 zygapophysis projects proportionally further beyond the articular surface (z) : the 

 neural spine {ns) is much lower, and beyond the anterior third of the trunk the 

 hypapophysis {h) subsides into a ridge, with its point produced backwards beneath 

 the articular ball of the centrum ; the zygantra {za, fig. 15) are distinct cavities. 



In the Coluber elapJms (PI. 2, figs. 17-20) the trunk- vertebrae are distinguished by 

 the great extent to which the part of the diapophysis {d", fig. 18) which underprops 

 the zygapophysis {z) is produced beyond the articular surface, the lower end of the 

 diapophysis {d') is less produced ; the hypapophysis, beyond the anterior fourth part 

 of the vertebral column, is reduced to a straight ridge, (fig. 20, h), extending along the 

 middle of the under surface of the centrum, and not produced posteriorly : a groove 

 separates the ridge on each side from the diapophysis and the posterior ball of the 

 centrum. Both the cup and ball and the articular part of the diapophysis are relatively 



