In the modern amphibians, the teeth are simple cones set 

 in a broad alveolar groove and attached in the pleurodont 

 style to the outer wall of that groove. In Necturus, Crypto- 

 branchus, or the frog, the crown of the tooth is easily broken 

 off the root portion (Figure 8-62). The abscission line marks 

 the division between the enamel crown and the base. In 

 Necturus the crowns are longer and straighter than in the 

 frog or Cryptobranchus. The larval anuran is of interest in 

 that it develops keratinized teeth (Figure 8-63). These are 

 not comparable to those of the agnath and can be viewed 

 as a larval specialization. 



Reptiles 



Reptile teeth are usually simple cones (haplodont) with 

 an enamel cap and an orthodentine interior enclosing a 



large pulp cavity. The teeth are set in a deep alveolar 

 groove, and their attachment to the jaw varies. The usual 

 style is identified as pleurodont (Figure 8-64); that is, the 

 teeth are attached to the outer wall of the alveolar groove. 

 This style is observed also in the living amphibians. In the 

 thecodont style, the tooth is set in a socket, as in the alli- 

 gator (Figure 8-65). Tupinambis, a lizard, has a subthecodont 

 style in which the tooth is fused all around to a bony sheath 

 covering the alveolar groove. The last style is the acrodont; 

 in this the teeth are fused all around to basal material fill- 

 ing the alveolar groove. 



Tooth replacement in the reptiles is of interest. In the alli- 

 gator one sees several generations (polyphyodont); the old 

 tooth which is fused to the upper margin of the tooth socket, 

 the alveolus; the replacement tooth which lies in a cavity 

 at the base of this large tooth; and a third generation lying 



dentine 



Figure 8-58. External view. A, of a tooth of Lepisosleus with sections showing structure neor tip, 

 B, middle, C, and base D. 



compact dentine 

 globular layer 



iompoct dentine 



Figure 8-59. External appearance of tooth of Osteolepis, A, with sections near tip, B, and at base, 

 C. A part of the wall of C is enlarged in D to show histological detail. (After Bystrow) 



TEETH • 249 



