TEETH. 



887 



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 Colubers, 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 

 Drymus nasutus,afev/ small teeth are present 

 on the ecto-pterygoid as well as on the 

 pterygoid. 



In certain genera of non-poisonous ser- 

 pents, as Dryophis, Dipsos, 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. 



In most of the Colubn, each maxillary and 

 premandibular bone includes from twenty to 

 twenty-five teeth. They are less numerous 

 in the genera Tortrix and Homalopsis, and are 

 reduced to a still smaller number in the 

 poisonous serpents, in the typical genera of 

 which the short maxillary bone supports only 

 a single perforated fang. 



Odontoyranliy, pi. 



. G & 7. 



Poisonous Serpents. The transition to 

 these serpents, which was begun in the 

 Buccphali and allied genera with grooved 

 maxiliary teeth, is completed by the poisonous 

 serpents of the genera Pelamis, Hydrophis, 

 Elaps, Boiigarits, and Hamadryas. 



The superior maxillary bone diminishes in 

 length with the decreasing number of teeth 

 which it supports. 1'he ecto-pterygoid bone 

 elongates in the same ratio, so as to retain its 

 position as an abutment against the shortened 

 maxillary, and the muscles implanted into this 

 external pterygoid bone communicate through 

 it to the maxillary bone the hinge- like 

 movements backwards and forwards upon 

 the ginglymoid articulations connecting that 

 bone with the prefrontal and palatine bones. 

 As the fully-developed poison -fangs are at- 

 tached by the same firm basal anchylosis to 

 maxillary sockets, which forms the charac- 

 teristic mode of attachment of the simple or 

 solid teeth, they necessarily follow all the 

 movements of the superior maxillary bone. 

 When the external pterygoid is retracted, the 

 superior maxillary rotates backwards, and the 

 poison-fang is concealed in the lax mucous 

 gum, with its point turned backwards. When 

 the muscles draw forward the external ptery- 

 goid, the superior maxillary bone is pushed 

 forwards, and the recumbent fang withdrawn 

 from its concealment and erected. 



In this power of changing the direction of 

 a large tooth, so that it may not impede the 

 passage of food through the mouth, we may 

 perceive an analogy between the viper and 

 the Lophius ; but in the fish the movement 

 is confined to the tooth alone, and is depen- 

 dent on the mere physical property of the 

 elastic medium of attachment; in the serpent 

 the tooth has no independent motion, but 

 rotates with the jaw, whose movements are 

 governed by muscular actions. In the fish 

 the great teeth are erect, except when pressed 

 down by some extraneous force. In the ser- 

 pent the habitual position of the fang is the 

 recumbent one, and its erection takes place 

 only when the envenomed blow is to be 

 struck. 



A true idea of the structure of a poison- 

 fang will be formed by supposing the crown 

 of a simple tooth, as that of a boa, to be 

 pressed flat, and its edges to be then bent 

 towards each other, and soldered together so 

 as to form a hollow cylinder, or rather cone, 

 open at both ends. The flattening of the 

 fang and its inflection around the poison-duct 

 commences immediately above the base, and 

 the suture of the inflected margins runs along 

 the anterior and convex side of the recurved 

 fang, as shown in Jig. 567, A. : the poison- 

 canal is thus in front of the pulp-cavity, as 

 shown in the longitudinal .section of the fang 

 B. The basal aperture of the poison-canal v 

 is oblique, and its opposite outlet v' is still 

 more so, presenting the form of a narrow 

 elliptical longitudinal fissure terminating at a 

 short distance from the apex of the fang. 

 The relative position of the two apertures 

 of the poison-canal is shown in the figure of 



SL 4 



