18. A caudal vertebra of a Tunny (Thyitntu vulgarix), in which all the osMt'x-d part* 



present a smooth surface and compact tissue ; each side of the centrum show s 

 two wide and deep depressions : smaller but deep unossifiod portions vacui- 

 ties in the dried vertebra extend from the neural and h:rmnl surfaces into 

 the substance of the centrum. Both neural and ha-inal arches have coalesced 

 with the ossified centrum. lluntman. 



19. The last abdominal and the anterior caudal vertebrae of a lx>ny Fish, showing a 



remarkable compression of the bodies of the vertebra?, which have a strong 

 longitudinal ridge on each side. Tin- bent-down but diverging parapophyses 

 are united in each of the abdominal vertebrae by a transverse osseous ridge 

 in the caudal vertebrae they converge and coalesce as usual to form the ha-mal 

 canal. J/unferian. 



20. The caudal vertebrae of a bony Fish with cylindrical centrums, having a finely - 



reticulated exterior : the neural and lurmul arches and spines are symmetri- 

 cally developed. Hunterian. 



21. The terminal caudal vertebrae of a bony Fish, in which the neural and haemal 



spines of the last two vertebrae are supported by a single centrum upon a com- 

 pressed and expanded triangular bony plate. Hunterian. 



J -' The terminal vertebrae of the same species of bony Fish, showing the same de- 

 gree of coalescence and metamorphosis of the neural and haemal arches for the 

 support of the rays of the caudal fin. llunltria*. 



23. A vertebra of a Reptile the fourth cervical of a Crocodile, in which the com- 

 pletely ossified centrum (r) presents an anterior concavity and a posterior con- 

 vexity, the vertebrae being united by ball-and-socket joints. The centrum 

 sends out a short inferior transverse process or ' parapophysis ' (pp) on each 

 side ; and a ' hypapophysis' (hp) or spinous process from its under part : the 

 neurapophyaes (**) have coalesced with their spine (//*), but still continue ar- 

 ticulated by suture with the centrum ; each developes a superior transverse 

 process or ' diapophysis ' (</</), and anterior and posterior oblique or articular 

 processes, 'zygapophyses' (zy), from their summit. There is on each side a 

 4 pleurapophysis' (pi), or rudimental cervical rib, articulated by its head to the 



