232 POISONOUS SERPENTS. 



part of the tooth the calcigerous tubes describe their various inflections 

 in a plane transverse to the axis of the tooth ; but towards the apex they 

 begin gradually to rise from that plane ; and as the pulp-cavity re- 

 ^ssumes, with the tooth itself, the simple conical form beyond the 

 termination of the poison-canal, the calcigerous tubes extend to 

 equal distances from the linear remnant of the pulp-cavity, which has 

 again passed to the centre of the tooth, and those tubes which are 

 continued from its continued extremity, pass to the apex of the fang in 

 a line parallel with the axis of the tooth. The calcigerous tubes 

 present secondary curvatures of a slightly wavy character, which 

 become more marked and irregular near their termination. In 

 whatever part of the section an entire tube could be clearly traced to 

 its termination, it formed an anastomotic loop at the periphery of 

 the dentine with an adjoining tube. The calcigerous tubes present a 

 diameter of the i5;5ooth of an inch, and they are separated by interspaces 

 equal to four of their own diameters. Each calcigerous tube gives off 

 many primary branches in its course, but is rarely seen to divide dicho- 

 tomously until it begins to form its irregular sinuosities near the peri- 

 phery of the tooth. In the transverse section figured, the primary 

 branches were sent off from the concave side of the tube, at an 

 acute angle with the trunk : the secondary smaller and more nume- 

 rous branches proceed from the same side of the main tube or of its 

 primary branches, at a less acute angle, into the clear uniting sub- 

 stance; they are remarkably parallel with each other and straight. 

 In old poison-fangs the pulp-cavity or fissure is obliterated by ossifica- 

 tion of the remains of the pulp. 



The external layer of cement is very thin where it covers the crown 

 of the tooth ; it is best seen at the line of union of the coadapted 

 margins of the inflected tooth c. At this part the cement is more 

 abundant in the viper's tooth, and its transparency permits a bristle 

 inserted into the poison-canal to be seen through it. The layer which 

 coats the inflected surface of the fang is thinner than the outer one, 

 which, from its transparency, has been regarded as enamel. (1) 



(4) " I should observe," says Mr. Smith, " that the poison-tube is not coated with enamel, 

 for the capsule in which the tooth is formed, and from the inner surface of which it is well known 

 that the enamel is deposited, does not pass between the edges of the slit into the poison tube ; as. 



