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DEVELOPMENT OF THE SKELETON OF THE TUATARA. 
PEATE I. 
SPHENODON PUNCTATUS.—VERTEBRAL COLUMN AND RIBS, GASTRALIA, AND TEETH. 
a., arch of atlas ; ab.’, abdominal rib, median portion ; ab.", abdominal rib, lateral portion ; 
a 1701 oN bt jes . Omer I = 
c.au., auditory capsule; d., dentary; ¢€.0., exoccipital; g.t., gastralia tissue tracts; ¢.p.', median 
intercentrum; ip.', chevron-bone; m., costo-cervical muscle ; m.', ligament of costo-cervical 
muscle; mk., Meckel’s cartilage ; ma., maxilla; my., myeclon (spinal cord) ; 2’, first spinal nerve ; 
nvii., twelfth cranial nerve; .a., neural arch ; xe., notochord; ne.e., chordal epithelium ; z<.s., 
chordal sheath ; n.p., intravertebral chordal plate ; 2.s., neurocentral suture ; 0.v., osseous vertebra ; 
p.a,, pro-atlas ; px., premaxilla; 7.c., cervical rib; 7.¢ed., caudal rib; 7.s., sacral rib; 7.¢., trunk rib; 
t.a., interarticular tissue ; ¢.ch., cheek-tooth ; ¢.d., developing tooth; ¢,f., fully-formed tooth (fused 
with bone); ¢.i., inner incisor; ¢.m., middle incisor; ¢.0., outer incisor; ¢.p., transpalatine ; 
u.p., wncinate process. 
Fig. 1. 
Fig. 2 
Vig. 3 
Fig. 4. 
Higaao: 
PieGs 
Fig. 7. 
Fig. 8 
Fig 
Fig. 10. 
Fig. 11 
Fig. 12 
Stage S. Anterior cervical vertebre :—The first five vertebre showing anterior cervical 
ribs, lateral aspect. s< fk 
Stage T. The same:—'The first 5-6 vertebre showing osseous and so-called ligamentous 
cervical ribs from left side, ventro-lateral aspect. x 4. 
Stage S. The “ Pro-Atlas” :—Wateral longitudinal section, including the exoccipital. 
x 20. 
Stage S. The Ribs :—Transverse section of last presacral vertebral segment. x 20: 
Stage S. The same :—Transverse section of the second sacral vertebral segment. x 20. 
Stage S. The same :—Transverse section of the fourth caudal vertebral segment. x 20. 
Stage R. Uncinate process :—Section through a poststernal rib showing development of 
uncinate process. x 25. 
Stage S. Abdominal ribs :—Ventral aspect of ribs 3-5. x 8. 
Stage S. The same :—Venutral aspect of ribs 16-18 of right side. x Il. 
Stage T. The same :—Venutral aspect of ribs 7-16 showing irregular union of parts. xX 2. 
Stage R. Notochordal plate :—Transverse section showing first origin. x 40. 
Stage S. The same :—Transverse section at full formation. x 25. 
Stage S. Chevron-bones :—Transverse section showing attachment to fourth caudal 
vertebra. x has 
Stage S. Incisor teeth :—Front aspect. Bs 
Stage T. The same :—Front aspect. x 4. 
Stage T. The same:—Median longitudinal section through second upper incisor and 
associated parts. xX 28. 
Stage T. Mavillo-palatine teeth :—Combined drawing—the teeth already confluent with 
the bone being indicated in outline, the developing teeth in colour. 4 13). 
Stage S. Cheek-looth :—Transverse section, including dentary and Meckel’s cartilage. 
x 20. 
