14 ANATOMY OF A CHELONIAN. 



ends with the costal plates of the second dorsal verte- 

 bra, the first vertebra having no costal plates of its 

 own. 



15. The tenth dorsal vertebra is comparatively wide 

 and short, and carries a pair of small ribs which have 

 no costal plates of their own, but anchylose with the 

 eighth pair of costal plates {i.e.^ those of the ninth 

 dorsal vertebra). On the ventral aspect of each of 

 these last costal plates is to be seen a small elevation, 

 over which the sacral ribs (i6) glide in lateral move- 

 ments of the pelvis. 



16. The two Sacral Vertebrae may be found still at- 

 tached to the carapace, or one or both may have come 

 away with the tail in preparing the specimen. Each 

 has a pair of short ribs, which run outward and end in 

 cartilages — which, in the articulated specimen, will be 

 seen to articulate with the iliac bones (71, a). That 

 end of each rib next the vertebral centrum is also car- 

 tilaginous. The anterior rib is much stouter than the 

 other. 



17. Take the carapace to bits, piece by piece, noting 

 meanwhile the finely dentated sutures by which most of 

 the bones articulate. As you separate the pieces, note 

 also that — 



a. The neural arch of the first dorsal vertebra 

 is much shorter than the centrum, which is 

 overlapped in front by the posterior end of 

 the nuchal plate, and behind by the neural 

 plate of the succeeding vertebra, the spine of 

 the first dorsal vertebra not expanding to make 



