POISON APPARATUS 895 
hollow, for transmission of the venom; but the construction 
of the tube is not as if a hole had been bored through a solid 
tooth. It is in effect a flat tooth with the edges rolled over 
together till they meet, converting an exterior surface, first 
into a groove, finally into a tube. This is shown, on micro- 
scopic examination of a section of the tooth, by the arrange- 
ment of the dentine. Unlike an ordinary tooth, the fang is 
movable, and was formerly supposed to be hinged in its 
socket, since it is susceptible of erection and depression. But 
the tooth is firmly socketed, and the source of this move- 
ment is the maxillary bone itself, which rocks to and fro by 
a singular contrivance. The maxillary is a small, stout, tri- 
angular bone, movably articulated above with a smaller one, 
the lachrymal, which is itself hinged upon the frontal. Be- 
hind, the maxillary articulates with the palatal and pterygoid, 
both of which are of rod-like shape, and are acted upon by 
the spheno-pterygoid muscle, the contraction of which pushes 
them forward. This forward impulse of the palatal and 
pterygoid is communicated to the maxillary, against which 
they abut, causing the latter to rotate upon the lachrymal. 
In this rocking forward of the maxillary, the socket of the 
fang, and with it the tooth itself, rotates in such manner 
that the apex of the tooth describes the arc of a circle, and 
finally points downward instead of backward. This pro- 
trusion of the fang is not an automatic motion, consequent 
upon mere opening of the mouth, as formerly supposed, but 
a volitional act, as the reverse motion, namely, the folding 
back of the tooth, also is; so that, in simply feeding, the 
fangs are not erected. The folding back is accomplished by 
the ecto-pterygoid and spheno-palatine muscles, which, 
arising from the skull behind as a fixed point of action, in 
contracting draw upon the jaw-bones in such a way that the 
maxillary, and with it of course the fang, are retracted, when 
the tooth is folded back with an action comparable to the 
