76 DEVELOPMENT OF THE SKELETON OF THE TUATARA. 



EXPLANATION OF THE PLATES 1 . 



PLATE I 



SPHENODON PUNCTATUS. VERTEBRAL COLUMN AND RIBS. 



a., arch of the atlas; a., body of atlas (odontoid peg) ; c.c., caudal canal; c.v., cartilaginous 

 vertebra; /./., fibrous tissue; h.a., accessory hypapophy sis; i.p., primary intercentrum ; i.p.', median 

 intercentrum ; i.p.", chevron-bone ; i.s., secondary intercentrum ; i.sg., interseptal segment ; 

 my., myelon (spinal cord); n.a., neural arch; nc. t notochord ; nc.e., chordal epithelium; nc.s., 

 chorda! sheath ; n.p., intravertebral chorda! plate ; n.p.', intervertebral chordal plate; n.sp., neural 

 pine; oc.c., occipital condyle ; o.v., osseous vertebra; r.cd., caudal rib ; r.s., sacral rib ; r.t., trunk 

 rib; *./., splitting lamina; s.o., skeletogenous sheath; t..a., interarticular tissue; v.c., vesicula 

 centralis. 



Fig. 1. Stage P. Vertebral Column : Lateral longitudinal section at about the region of 



vertebrae 6-8. X 50. 



Fig. 2. Stage P. The same -. Median longitudinal section through the region of fig. 1. x 50. 

 Fig. 3. Stage P. The same : Transverse section through the intervertebral region of caudal 



segments 23. x 40. 



Fig. 4. Stage P. The same : Section through a vertebral region the 6th segment in front of 



fig. 3. X 40. 



Fig. 5. Stage Q. Vertebral Column : Lateral longitudinal section in the region of vertebrae 



20-23. x 40. 



Fig. 6. Stage Q. The same : Median longitudinal section through vertebrae 20-23. x 40. 



Fig. 7. Stage Q. The same: Longitudinal section (slightly oblique) through caudal vertebrae 



3-6. x 40. 



Fig. 8. Stage Q. The same : Median longitudinal section through the basi-occipital and the 



four anterior cervical vertebrae. x 40. 



Fig. 9. StageS. Vertebral Column: Longitudinal section through the basi-occipital and the 



three anterior cervical vertebrae. X 25. 



Fig. 10. Stage S. The same : Median longitudinal section through vertebrae 13-15. x 25. 



Fig. 11. Stage S. The same : Transverse section through the intervertebral region 5-6. x 25. 

 Fig. 12. Stage S. The same : Ventral aspect of the last presacral to the 9th caudal vertebrae 



showing free caudal ribs. X 5. 



Fig. 13. Stage T. Vertebral Column : Median longitudinal section through vertebrae 7-10. X 18. 

 Fig. 14. Stage T. The same-. Median longitudinal section through intercentrum 8-9 of fig. 13, 



showing minute structure. x 50. 



Fig. 15. Adult. Vertebral Column : Median longitudinal section through vertebra 9-11. x 11. 

 Fig. 16. Adult. The same : Ventral aspect of the 10th to the 20th vertebrae showing an abnormal 



condition of the intercentra. | nat. size. 



Fig. 17. Adult. The same : Median longitudinal section at about the region of the 12th caudal 



vertebra. v K 



*"V C/ 



Fig. 18. Adult. The same : Caudal vertebrae 7-12 from the left side. f nat. size. 



Fig. 19. Adult. The same : Transverse section through plane a-b of fig. 17. x 11. 



Fig. 20. Adult. The same : Caudal vertebra 11 from the left side. f nat. size. 



Fig. 21. Adult. The same : Caudal vertebra. nat. size. 



1 In all the Plates, where colouring has been employed, blue indicates hyaline cartilage and yellow bone, 

 with the exception of PI. I. fig. 13. 



