290 



REPTILIA. 



in which the superior maxillary teeth increase 

 in size towards the posterior part of the bone, 

 the large terminal teeth of the series are tra- 

 versed along their anterior and convex side 

 by a longitudinal groove. In the Bucephalus 

 capemis the two or three posterior max- 

 illary teeth present this structure, and are 

 much larger than the anterior teeth, or those 

 of the palatine or premandibular series ; they 

 add materially to the power of retaining their 

 prey, and may conduct into the wounds 

 which they inflict an acrid saliva, but they 

 are not in connexion 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 Colubri 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. 



In the poisonous serpents the superior 



Fig. 209. 



Roof of the mouth of the Rattlesnake, showing the 

 Series of palatine Teeth. 



The sheath of the poison fang (11), opened to 

 show the poison fang (12). Oil the opposite side 

 the sheath (1(1) is represented entire; h h, external 

 pterygoid muscles; v v, anterior adductor muscle of 

 the rami of the lower jaw. 



maxillary bone diminishes in length with the 

 decreasing number of teeth which it supports. 

 The transverse or external 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 style communicate, 

 through it, to the maxillary bone the hinge- 

 like movements backwards and forwards upon 

 the ginglymoid articulations connecting that 

 bone with the anterior frontal, and palatine 

 bones. As the fully-developed poison fangs 

 are attached by the same firm basal anchylo- 

 sis to shallow maxillary sockets, which forms 

 the characteristic mode of attachment of 

 the simple or solid teeth, they necessarily 

 follow all the movements of the superior 

 maxillary bone. When the external ptery- 

 goid 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 pterygoid, the 

 superior maxillary bone is pushed forwards, 

 and the recumbent fang withdrawn from its 

 concealment and erected. 



The peculiar structure of the poison fang 

 was first described by Fontana as it exists in 

 the viper, and subsequently received ad- 

 ditional elucidation by Mr. Smith's careful 

 examination of the fangs of the Hydrus, 

 Naja, and Crotalus, and by Mr. Clift's illus- 

 trative drawings appended to Mr. Smith's 

 Paper. 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 edijes to be then bent 

 towards each other, and soldered together, so 

 as to form a hollow cylinder open at both 

 ends. 



The flattening of the fang, and its inflection 

 around the poison-duct, commences imme- 

 diately above the base, and the suture of the 

 inflected margins runs along the anterior and 

 convex side of the recurved fang ; the poison 

 canal is thus in front of the pulp cavity. 

 The basal aperture of the poison canal is 

 oblique, and its opposite outlet is still more 

 so, presenting the form of a narrow elliptical 

 longitudinal fissure, terminating at a short dis- 

 tance from the apex of the fang. The rela- 

 tive position of the two apertures of the 

 poison canal is shown in the figure of the 



:. 210. 



Structure of the poison-teeth of the Serpent. 



a, longitudinal section of poison fang ; b, shows 

 a hair inserted into the poison canal ; c, trans- 

 verse section of fang. 



