78 DEVELOPMENT OV THE SKELETON OF THE TUATARA, 



TLATE II. 



SpHENODON PUNCTATUS. — VERTKBBAL COLUMN AND EIBS, GASTRALIA, AND TEETU. 



«., arch of atlas ; ai/, abdominal rib, median portion; ai.", abdominal rib, lateral portion; 

 call., auditory capsule; d., dentary ; e.o., exoccipital; ffJ., gastralia tissue tracts; i./>.', median 

 intercentrura ; i.p.", chevron-bone; m., costo-cervical muscle; m.', ligament of costo-cervical 

 muscle; mk., Meckel's cartilage; mx., maxilla; my., myelon (spinal cord) ; nJ, first spinal nerve; 

 n-xii., twelfth cranial nerve; ».«., neural arch; nc, notochord; nc.e., chordal epithelium; nc.s., 

 chordal sheath ; n.p., intravertebral chordal plate ; n.s., neurocentral suture; o.v., osseous vertebra; 

 j[;.«., pro-atlas; ;w., premaxilla; ?-.c., cervical rib ; r.ct?., caudal rib ; ?•.*., sacral rib ; r.^, trunk rib ; 

 /.a, interai-ticular tissue ; if.c,^., cheek-tooth ; i.rf., developing tooth; ;./., fully-formed tooth (fused 

 with bone); t.i., inner incisor; i.m., middle incisor; t.o., outer incisor; t.p., transpalatine ; 

 ii.p., uncinate process. 



Fig. 1. Staffe S. Anterior cervicoJ vertebrtB : — The first five vertebrse showing anterior cervical 



ribs, lateral aspect. x 8. 



Fi"'. 2. Stage T. The same : — The first 5-6 vertebrae showing osseous and so-called ligamentous 



cervical ribs from left side, ventro-lateral aspect. x 4. 



Fig. 3. Stages. The " Pro- Atlas " : — Lateral longitudinal section, including the exoccipital. 



X 20. 

 Fig. 4. Stage S. The Ribs : — Transverse section of last presacral vertebral segment. x 20. 



Fig. 5. Stage S. The same : — Transverse section of the second sacral vertebral segment, x 20. 

 Fig. 6. Stage S. The same : — Transverse section of the fourth caudal vertebral segment, x 20. 

 Fig. 7. Stage R. Uncinate process : — Section through a poststernal rib showing development of 



uncinate process. x 25. 



Fig. 8. Stage 8. Abdominal ribs : — Ventral aspect of ribs 3-5. x 8. 



Fig. 9. Stage S. The same : — Ventral aspect of ribs 16-18 of right side. X 1 1. 



Fig. 10. Stage T. The same: — Ventralaspect of ribs 7-16 showing irregular union of parts, x 2. 

 Fig. 11. Stage R. Notochordal plate : — Transverse section showing first origin. x 40. 



Fig. 12. Stage S. The same : — Transverse section at full formation. X 25. 



Fig. 13. Stage S. Chevron-bones : — Transverse section showing attachment to fourth caudal 



vertebra. x 25. 



Fig, 14. Stage S. Incisor teeth : — Front aspect. X 5. 



Fig. 15. Stage T. The same : — Front aspect. X 4. 



Fig. 16. Stage T. The same : — Median longitudinal section through second upper incisor and 



associated parts. x 23. 



Fig. 17. Stage T. Maocillo-palatine teeth : — Combined drawing — the teeth already confluent with 

 the bone being indicated in outline, the developing teeth in colour. x 13. 



Fig. 18. Stage S. Cheek-tooth : — Transverse section, including dentary and Meckel's cartilage. 



X 20. 



