378 
ME. CHAELES S. TOMES ON THE DEVELOPMENT AND 
this year, I have discussed the qualifications which need to be made before we can 
accept Prof. Owen’s description of the development of these or any other reptilian teeth, 
I have simply quoted his words here, as embodying what is commonly known of the 
development of poison-fangs. 
Venomous snakes are divided into two groups — the venomous colubrine snakes, in which 
the poison-fang is attached to a fixed maxillary bone, so that it is always erect, and the 
viperine snakes , in which the maxillary bone carries no other teeth than the poison- 
fang, and is capable of a rotary motion, by which its fang is erected or laid recumbent 
(Gunther’s ‘Reptiles of British India,’ Ray Society, p. 165). 
I have had better opportunities of investigating the poison-fangs of the viperine snakes 
than of the venomous colubrines, of which latter the cobra is the only one which I have 
been able to procure in a perfectly fresh condition ; but, as I shall presently show, there 
would appear to be well-marked differences in the succession between the two groups *. 
The relations of poison-fangs to their successors may be most advantageously studied in 
transverse sections, the specimens having been previously hardened and decalcified in 
chromic acid. 
The appearance presented will vary, according as the section is near to the tip or to 
the base of the fang. I will commence by the description of a section taken midway in 
the length of the poison-fang of a rattlesnake (Plate 37. fig. 2). 
The figure embraces that which would appear to the naked eye as an elevation when 
looking into the mouth of the snake — that is to say, the recumbent tooth covered in by 
its loose fold of mucous membrane ( c in the figure) and the subjacent region where lie 
the successional teeth. At the upper part of the figure the poison-fang at present in 
use ( i ) is seen lying in a chamber in the mucous membrane, and since it is recumbent 
and parallel to the long axis of the jaw, it is in transverse section. Beneath it (or, as it 
would stand in the snake’s mouth, above it) are a series of eight teeth of various ages, all 
seen in transverse section, the oldest lying nearest to the tooth already in use. 
The successional teeth are not arranged in a single series, as would be the case in the 
ordinary serial teeth of the jaws (cf. my paper in Phil. Trans. 1875), but in a double 
row, being obviously placed in pairs. 
A more careful inspection of one of these pairs will disclose that although there is no 
very great difference, yet one of the teeth is a little more advanced than the other. 
Thus in fig. 2 No. 2 is a little more advanced, both in development and in position, than 
No. 3, and is the tooth destined to be the next to move into its place and enter upon 
work. Lower down in the series this difference in point of development is less apparent ; 
indeed the two constituting a pair are generally advanced to about the same stage in 
their construction. 
I have affixed numbers to the several tooth-germs shown in figs. 1 and 2 to indicate 
* I have examined several specimens of Hydrophis which were preserved in spirit, and believe the arrange- 
ment of the successional teeth to he similar to that observed in Cobra ; hut specimens long kept in diluted 
spirit are ill-suited for such investigations. 
