886 



TEETH. 



gigantic Salamander and of the Alligator ; and 

 the outer surface of the bones was strongly 

 sculptured, as in the Crocodilian family, but 

 of a relatively larger and coarser pattern. 

 -The upper jaw contains a single row of small 

 teeth, about sixty in number, anterior to which 

 are three or four large conical tusks. The 

 bases of the serial teeth project directly from 

 the outer wall of the shallow socket, there 

 being no alveolar ridge external to it. The 

 second large anterior tusk is three times the 

 size of the first of the serial teeth, and the 

 size of these teeth gradually diminishes as 

 they are placed further back ; the length of 

 the common-sized teeth being about two lines, 

 and the greatest breadth one-third of a line. 

 The Epical two-thirds of each tooth is smooth, 

 but the basal third is fluted and anchyiosed 

 to the outer wall of the socket. The osseous 

 roof of the mouth is principally composed of 

 a pair of broad and flat bones, homologous 

 with the divided vomer in Batrachia, but of 

 much greater relative extent, approaching, in 

 this respect, those of the Menopome, and de- 

 fending the mouth with a more extensive 

 roof of bone than exists in any Lacertian 

 reptile ; physiologically, therefore, the La- 

 byrinthodon, in this part of its structure, 

 comes nearest to the Crocodile ; but the 

 structure itself, morphologically, is essen- 

 tially Batrachian.* In the Menopome f and 

 gigantic Salamander, a row of small teeth ex- 

 tends transversely across the anterior extre- 

 mity of the vomerine bones ; and the occur- 

 rence in the Labyrinthodon of a similar row, 

 consisting in each palatine bone of three 

 median small teeth and two outer larger ones, 

 marks most strongly its Batrachian nature j 

 and from the outermost tooth a longitudinal 

 row of small and equal-sized teeth is con-* 

 tinued backward along the exterior margin of 

 the palatine bone. The whole of this series 

 of palatal teeth is nearly concentric with the 

 maxillary teeth. 



In Lacertine reptiles the examples of a 

 row of palatal teeth are rare, and, when pre- 

 sent, it is short, and situated towards the 

 back of the palate, upon the pterygoid bones, 

 as in the Iguana and Mosasaur. J In Batra- 

 chians the most common disposition of the 

 palatal teeth is a transverse row placed at the 

 anterior part of the divided vomer, as in Frogs, 

 the Menopome and gigantic Salamander, and 

 at the posterior part in certain toads. In the 

 Amphiume, on the contrary, the palatal teeth 

 form a nearly longitudinal series along the 

 outer margin of the palatine bones. The 

 Labyrmthodon combines both these disposi- 

 tions of the palatal teeth. The lower jaw, 

 like the upper, contains a series of small 

 teeth, with a few larger tusks anterior to them, 

 the serial teeth are long and slender, gradually 

 diminishing in size towards the anterior por- 

 tion of the jaw ; the largest fossil portion 

 which I have obtained presents a linear series 

 of not less than fifty sockets, placed alter* 



* Odontography, pi. 63. A, fig, 3. 

 t Ib. pi. 62. figs. 1 & 2. 

 | Ib.pl. 68. 



nately, one nearer the inner, the next nearer 

 the outer side of the jaw. The sockets of 

 the teeth are shallower than in the upper 

 jaw ; the outer wall is more developed than 

 the inner, and the anchylosed bases of the 

 teeth more nearly resemble, in their oblique 

 position, those of existing Batrachia. With 

 regard to the modification of the microscopic 

 structure of the teeth, I may observe that, 

 between the apex and the part where the 

 inflected vertical folds of the cement com- 

 mence, the tooth resembles, in the sim- 

 plicity of its intimate structure, that of the 

 entire tooth of ordinary Batrachia and most 

 reptiles ; and in the lower or basal half of the 

 tooth the labyrinthic structure above de- 

 scribed commences, and gradually increases 

 in complexity. 



In the genus Deirodon*, the teeth of the 

 ordinary bones of the mouth are so small 

 as to be scarcely perceptible ; and they appear 

 to be soon lost, so that it has been described 

 as edentulous, and has been called " Anodon." 

 An acquaintance with the habits and food 

 of this species has shown how admirably 

 this apparent defect is adapted to its well- 

 being. Its business is to restrain the undue 

 increase of the smaller birds by devouring 

 their eggs. Now if the teeth had existed 

 of the ordinary form and proportions in the 

 maxillary and palatal regions, the egg would 

 have been broken as soon as it was 

 seized, and much of the nutritious contents 

 would have escaped from the lipless mouth 

 of the snake in the act of deglutition ; but, 

 owing to the almost edentulous state of the 

 jaws, the egg glides along the expanded 

 opening unbroken ; and it is not until it has 

 reached the gullet, and the closed mouth 

 prevents any escape of the nutritious matter, 

 that the egg becomes exposed to instruments 

 adapted for its perforation. These instruments 

 consist of the inferior spinous pocessess (hyp- 

 apophyses) of the seven or eight posterior cer- 

 vical vertebrae, the extremities of which are 

 capped by a layer of hard cement, and pene- 

 trate the dorsal parietes of the oesophagus. 

 They may be readily seen, even in very 

 small subjects, in the interior of that tube, 

 in which their points are directed backwards. 

 The shell being sawed open longitudinally 

 by these vertebral teeth, the egg is crushed 

 by the contractions of the gullet, and is 

 carried to the stomach, where the shell is 

 no doubt soon dissolved by the acid gastric 

 juice. 



In the Boa Constrictor, the teeth are 

 slender, conical, suddenly bent backwards 

 and inwards above their base of attachment ; 

 the crown is straight or very slightly curved, 

 e. g. in the posterior teeth. The inter- 

 maxillary bone supports four small teeth ; 

 each maxillary bone has eight much larger 

 ones, which gradually decrease in size as they 

 are placed further back. There are eight 

 or nine teeth of similar size and proportions 

 in each premandibular bone. These teeth 



* The Coluber scaber of Linnaeus ; an arboreal 

 serpent of South Africa. 



