REPTILIA. 



28 & 



jaw are fixed together at the symphysis, and 

 are opposed by the usual vertical movement 

 to a similarly complete maxillary arch above : 

 these belong to the genera Amphisbcena and 

 Anguis of Linnaeus. The rest of the Ophi- 

 dians (true serpents), which form the typical 

 members, and by far the greatest proportion 

 of the order, prey upon living animals of fre- 

 quently much greater diameter than their own ; 

 and the maxillary apparatus is conformably 

 and peculiarly modified to permit of the 

 requisite distention of the soft parts sur- 

 rounding the mouth, and the transmission of 

 their prey to the digestive cavity. 



The two superior maxillary bones have 

 their anterior extremities joined by an elastic 

 and yielding fibrous tissue, with the small and 

 single intermaxillary bone ; the symphysial 

 extremities of the lower maxillary rami are 

 connected together by a similar tissue, allowing 

 of a still wider lateral separation. The op- 

 posite or posterior extremity of each ramus 

 is articulated to a long and moveable vertical 

 pedicle, formed by the tympanic or quadrate 

 bone, which is itself attached to the extremity 

 of a horizontal pedicle formed by the mastoid 

 bone, so connected as also to allow of a 

 certain yielding movement upon the cranium. 

 The palatine and pterygoid (d) bones have 

 similar loose and moveable articulations, 

 and concur with the other dentigerous bones 

 of the mouth in yielding to the pressure of the 

 large bodies with which the teeth may have 

 grappled. 



With the exception of the Deirodon scaber 

 and some congeneric species, in which the 

 teeth of the ordinary bones of the mouth are 

 so minute as to have been deemed wanting, the 

 maxillary and premandibular in all true Ophi- 

 dians are formidably armed with sharp- pointed 

 teeth ; there is on each side the palate a row 

 of similar teeth supported by the palatine and 

 pterygoid bones. In the great Pythons, and 

 some species of Boa, the intermaxillary bone 

 also supports teeth. 



All the teeth, whatever be their position, 

 present a simple conical form ; the cone being 

 long, slender, and terminated by an acute 

 apex ; and the tooth is either straight, or 

 more commonly bent a little beyond the base, 

 or simply recurved, or with a slight sigmoid 

 inflection. The teeth are thus adapted for 

 piercing, tearing, and holding, and not for 

 dividing or bruising. In some species, certain 

 teeth are traversed by a longitudinal groove 

 for conveying an acrid saliva into the wounds 

 which they inflict : in others, two or more 

 teeth are longitudinally perforated for trans- 

 mitting venom ; such teeth are called poison 

 fangs, and are always confined to the superior 

 maxillaries, and are generally placed near the 

 anterior extremity of those bones. 



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. An acquaintance with the habits 

 and food of this species has shown how ad- 

 mirably this apparent defect is adapted to its 



VOL. IV. 



well-being. Its business is to restrain the 

 undue increase of the smaller birds by de- 

 vouring their eggs. Now if the teeth had 

 existed of the ordinary form and propor- 

 tions in the maxillary and palatal regions, 

 the egg would have been broken as soon as 

 it was seixed, and much of its nutritious 

 contents would have escaped from the lip- 

 less mouth of the snake in the act of de- 

 glutition ; but, owing to the almost eden- 

 tulous 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 shell is exposed 

 to instruments adapted for its perforation. 

 These instruments consist of the inferior 

 spinous processes of the seven or eight pos- 

 terior cervical vertebrae, the extremities of 

 which are capped by a layer of hard cement, 

 and penetrate the dorsal parietes of the 

 resophagus : they may be readily seen, even 

 in very young 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 in- 

 wards above their base of attachment, with 

 the crown straight curved, as in the posterior 

 teeth. The intermaxillary bone supports 

 four small teeth ; each superior 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 pre- 

 mandibular 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, compressed antero- 

 posteriorly, and anchylosed to a shallow 

 alveolus, extending across the shallower 

 alveolar groove. An affinity to the lizard 

 tribes is manifested by the greater develop- 

 ment 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 at- 

 tached : 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 al- 

 ways 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. 



In certain genera of the non-venomous 

 serpents, as Dryophis, Dipsas, and Bucephalus, 



u 



