396 ANATOMY OF VERTEBRATES. 



traded, the superior maxillary rotates backward, and the poison- 

 fang is concealed in the lax mucous gum, with its point turned 

 backward, fig. 267, 10. AYhen the muscles draw forward the 

 external pterygoid, the maxillary bone is pushed forward, 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 recumbent fang withdrawn from its concealment and erected.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 de- 

 pendent 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, wdiose movements are governed by 

 muscular actions. In the fish the great teeth are erect, except 

 when pressed down by some extraneous force. In the serpent 

 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 

 fio\ 269, a : the poison-canal is thus in front of the pulp-cavity, as 

 shown in the longitudinal section of the fang, fig. 268, y, and 

 fig. 269, b. The basal aperture of the poison-canal, ib. 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 dis- 

 tance from the apex of the fang. In fig. 268, a fine hair is repre- 

 sented as passing through the poison-canal by the duct of the fang. 



The secretion of the poison-gland is conveyed to the basal aperture 

 of the poison-canal of the fang. "We may suppose, that as the 

 analogous lacrymal and salivary glands in other animals are most 

 active during particular emotions, so the rage which stimulates the 

 venom-snake to use its deadly weapon must be accompanied with 

 an increased secretion and great distension of the poison-glands ; 

 and as the action of the compressing muscles is contemporaneous 

 with the blow by which the serpent inflicts the wound, the poison 

 is at the same moment injected with force into the wound from 

 the apical outlet of the perforated fang. 



The duct which conveys the poison, although it runs through 



