! 
25 Dr. Gray’s Obfervations on the Clafs of 
examples of this. It muft, however, be con fe fled, that the gene- 
ral character of the head of the Boa, though differing very widely 
from that of thofe Colubri which are not venomous, is not 
quite that of the Crotalus ; but the difference, though very 
obvious to a perfon accuftomed to the examination of Serpents, 
is perhaps not eafy to be fully exprefled in words. It feems, 
however, to confift principally in a lateral compreffion, and 
elongation, of the anterior part of the head, fo as to form a 
kind of fnout. Hence the trivial name of canina is given by 
LiNNiEUS to one of the lpecies. 
From the characters of the head (as the trunk affords none 
deferving confideration) I fhall proceed to thofe of the other 
extremity. 
In the Crotali I have never found the tail (exclufive of the 
Rattle) to exceed one-ninth part of the whole length ; fome- 
timesl have found it much fhorter. In fome of the venomous 
Colubri, the proportion is ftill lefs. In the Atropos I found it 
only one-thirteenth. In the Englifh Viper (Coluber Berus) it 
Is commonly about one-feventh or eighth. In fome venomous 
lpecies, however, the proportion is fomething greater. In the 
Naja I have found it as much as one-fixth ; which proportion 
is, I believe, as great as I have ever obferved : but that I may 
he fare to keep within the truth, I will only fay, that I have 
never met with a venomous Serpent, the tail of which was 
equal to one-fifth of the whole length^. 
* The tail of the Boa contortrix is faid by Linnaeus to be one-third ; but his 
own enumeration of the Scuta fufficiently fhews that this mud: be an error. The 
Coluber Leberis, Dipfas, and my£terizans appear, by the number of fcales 
under their tail, to furnifh exceptions to what I have faid. The two firft I have 
never feen, but fufpedt they are not venomous ; that the lafl is not fo I am very - 
terrain, having examined many fpecimens of it. 
2 
With 
