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.i 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 Lahyrinthodon 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 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 niuch 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 vertebrw, 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 are separated by wide intervals, from which other teeth, similar to those in place, have been detached. The base of each of the above teeth is extended transversely, com pressed antero-posteriorly, and anchylosed to a shallow alveolus, extending obliquely across the shallower alveolar groove. An affinity to the lizard tribes is manifested by the greater development of the outer, as compared with the inner wall of the alveolar furrow.
The palatine teeth, of which there are three or four in each palatal bone, are as large as the superior maxillary, and are similarly attached. The pterygoid teeth, five or six in number, which complete the internal dental series on the roof of the mouth, are of smaller size, and gradually diminish as they recede backwards. In the interspaces of the fixed teeth in both these bones, the places of attachment of the shed teeth are always visible ; so that the dental formula, if it included the vacated with the occupied sockets, would express a greater number of teeth than are ever in place and use at the same time.* In the smaller species of Boa, the intermaxillary bone is edentulous.
The C'olubers, like other true serpents, have two longitudinal rows of teeth on the roof of the mouth, extending along the palatines and pterygoids. The genus Oligodon appears to form the sole exception to this rule. In the Dryinus nasutus, a few small teeth are present on the ecto-pterygoid as well as on the pterygoid.
In certain genera of non-poisonous ser pents, as Thyophis, Dipsas, and Bucephalus, in which the superior maxillary teeth increase in size towards the posterior part of the bone, the large terminal teeth of the series are traversed along their anterior and convex side by a longitudinal groove. In the Bu cephalus capensis, the two or three poste rior maxillary teeth present this structure, and are much larger than the anterior teeth, or those of the palatine and premandibular series. They add materially, therefore, to the power of retaining the prey, and may conduct into the wounds which they inflict an acrid saliva ; but they are not in con nection with the duct of an express poison gland. The long-grooved fangs are either firmly fixed to the maxillary bones, or are slightly moveable, according to their period of growth. They are concealed by a sheath of thick and soft gum, and their points are directed backwards. The sheath always contains loose recumbent grooved teeth, ready to succeed those in place.