76 DEVELOPMENT OF THE SKELETON OF THE TUATARA. 
EXPLANATION OF THE PLATES1?. 
PEATE SL, 
SPHENODON PUNCTATUS.—VERTEBRAL COLUMN AND RIBS. 
a., arch of the atlas; @., body of atlas (odontoid peg) ; ¢.c., caudal canal; c.v., cartilaginous 
‘vertebra ; f.t., fibrous tissue; /.a., accessory hypapophysis ; 7.p., primary intercentrum ; 7.p.’, median 
intercentrum ; i.p.”, chevron-bone; 7.s., secondary intercentrum ; i.sg., interseptal segment ; 
my., myelon (spinal cord) ; n.a., neural arch; ne., notochord ; ne.e., chordal epithelium; nc.s., 
chordal sheath ; n.p., intravertebral chordal plate ; ».p.', intervertebral chordal plate; n.sp., neural 
‘spine ; 9¢.c., occipital condyle ; 0.v., osseous vertebra; 7.cd., caudal rib; 7.s., sacral rib ; 7.¢., trunk 
rib; s./., splitting lamina; s.0., skeletogenous sheath; ¢.a., interarticular tissue; v.c., vesicula 
centralis. 
Fig. 1. Stage P. Vertebral Column :—ULateral longitudinal section at about the region of 
vertebrie 6-8. x 50. 
Fig. 2. Staye 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 2-3. 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 :—Uateral \ongitudinal section in the region of vertebre 
20-23. x 40. 
Tig. 6. Stage Q. The same :—Median longitudinal section through vertebrie 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 vertebree. x 40. 
Fig. 9. Stage S. Vertebral Column :—Longitudinal section through the basi-occipital and the 
three anterior cervical vertebre. x 25. 
Fig. 10. Stage S. The same :—Median longitudinal section through vertebre 13-15. x 25. 
Stage S. The seme :—Transverse section through the intervertebral region 5-6. — x 25. 
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.12. Stage S. The same :—Ventral aspect of the last presacral to the 9th caudal vertebre 
showing free caudal ribs. x 
Fig. 13. Stage T. Vertebral Column :—Median longitudinal section through vertebre 7-10. x 18. 
Fig. 14, Stage 7. 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 vertebre 9-11. x 11. 
Fig. 16. Adult, The same :—Ventral aspect of the 10th to the 20th vertebra showing an abnormal 
condition of the intercentra. 2 nat. size. 
Fig. 17. Adult. The same :—Median longitudival section at about the region of the 12th caudal 
vertebra. »< BF 
Fig. 18. Adult. The same :—Caudal vertebr 7--12 from the left side. 2 nat. size. 
Fig. 19. Adult. The same :—Transverse section through plane a- of fig. 17. <I. 
Fig. 20. Adult. The same :—Caudal vertebra 11 from the left side. ? nat. size. 
Fig. 21. Adult. The same :—Caudal vertebre. # nat. size, 
‘ In all the Plates, where colouring has been employed, blue indicates hyaline cartilage and yellow bone, 
with the exception of Pl. L. fig. 13, 
