64 PROF. G. B. HOWES AND MR. H. H. SWINNERTON ON THE 
(Pl. II. fig. 15), the outer tooth of each set being somewhat the larger of the three. At 
Stage S (fig. 14) all are seen to be free, and the outer still large. Beyond the mere 
inference of fusion, Dendy does not state the method by which he presumes these 
pointed incisors to be converted into the tusks of the adult. Asa rule each of the 
upper tusks, when fully formed, is doubly pointed (or, as remarked by Giinther, 
“ notched”) (cf. text-fig. 15), there being a smaller internal cone, anda larger external 
one somewhat backwardly curved (text-fig. 16). In the lower jaw there are three cones 
(text-fig. 16), a larger external and two smaller internal, the three teeth which are 
Fig. 17. 
Fig. 16. 
Fig. 18. 
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Illustrations of the dentition of Sphenodon, 
Fig. 15, Incisors, front aspect, old individual. Fig. 16. The same, younger individual, little worn. Both 
nat. size. Fig. 17, Enlarged sketch of upper incisors of fig. 16, x 6. Fig. 18. Complete adult dentition : 
nat, Size. 7, incisors; t.a., cheek-teeth, alternating series ; tu, cheek-teeth, structurally uniform series, 
present having united with the mandible. That portion of the dentary element which 
bears them becomes, with them, clothed in an enamel-like substance, which justifies 
Giinther’s remark (67, p. 602) that the alveolar edge of the mandible is polished. 
Tomes ! regards this substance as true bone. 
In the embryonic upper jaw the middle incisor present early ceases to elongate 
(cf. Pl. IL. fig. 15, tm.) and at Stage T it becomes loose. The reason of this is 
evident from the fact that longitudinal section (Pl. Il. fig. 16) shows it to be confluent 
' Tomes, C.: Dental Anatomy, ed. 4, 1894, p. 253. 
