PREFACE. 
Vll 
is, by sub-caudal and abdominal scuta. The Coluber, like the Boa, is furnished with abdomi¬ 
nal scuta; but on the under part of the tail, instead of scuta, it has sub-caudal squamae, which 
resemble scuta divided in the middle, and, in reckoning their number, are counted by pairs. 
In distinction to ordinary scales, the sub-caudal squamae have, by some, not unaptly, been 
termed scutellae. The Anguis has neither scuta nor scutellae; being, in general, covered uni¬ 
versally with uniform scales. 
These three genera are readily distinguished by their respective characters; but many diffe¬ 
rent serpents are so exactly alike in their shape and form, that it is very difficult to define the 
specific differences with tolerable precision. 
I have, throughout the descriptions, adhered to the usual practice of counting the scuta and 
squamae separately, as well as jointly; though not unaware how considerably the number 
varies in subjects of the same species: in the Cobra de Capello, for example, the variation is 
found to be eighteen or twenty. 
The shape of the head; the shape and site of the eyes and nostrils; the form and dimensions 
of the trunk and the tail; the size, form, and arrangement of the scales; have all been parti¬ 
cularly mentioned in the descriptions, though in a number of different species, very little, if 
any, variation is observable. 
The number of laminae of the head, in the species, is constantly the same, and the variation 
in shape not considerable; but the number, as well as shape, are so exactly the same in many 
different species, as renders both, at best, only vague marks of distinction. 
Colour, spots, bands, and fillets, in living, or recent subjects, appear to be distinctive marks 
the least subject to variation. The difficulty, however, of describing these precisely, in words, 
leaves it always desirable to have coloured drawings from the living reptile: for it should be 
remarked, that the colours of snakes (though not so rapidly as in fish) are very apt to fade soon 
after death, and in time to suffer great change from the spirits employed for the preservation of 
specimens. 
The poisonous serpents are sufficiently distinguished by their fangs; which, in the living 
animal, when held properly by the neck, or irritated, are readily enough discerned; though 
not always so easily, in their recumbent state, or in the dead subject. But the want of a row of 
teeth in the upper jaw, found in that of all harmless serpents, serves also as a criterion, even 
where the fangs have purposely been eradicated, or lost by accident. 
The ordinary teeth, or holders, common to all serpents, are nearly of the same shape ; curve, 
reflex, and sharp: but they vary in size and number, in different species. 
In serpents not venomous, there are three rows of common teeth in the upper jaw; one ex¬ 
terior, and two interior: the former, I have, in the descriptions, termed marginal; the latter, 
though in reality fixed in the jaw bone, I have, from their apparent situation in the undissected 
head, termed palatal. 
The palatal teeth, in a venomous serpent, are exhibited in the anatomical PlateXLV.; where 
the space occupied by the marginal row in the jaw of a harmless serpent, appears to be filled 
up by the poisonous fangs, and the sacs which envelop them. 
As the marginal row is invariably found in serpents not venomous, and the palatal rows are 
found in all serpents whatever, the constant repetition in the descriptions, respecting the teeth, 
might have been obviated by a general remark. But the subjects were examined at different 
times, while I was ignorant that poisonous serpents had no marginal row: for it was not till 
after my return from India, that I had the pleasure of finding the result, on a comparison with 
my own descriptions, accord exactly with the discovery communicated to the Royal Society in 
1 7 88 , by Dr, Gray, who had examined above one hundred and fifty specimens of serpents in the 
British Museum. The only exception I have met with to the general rule, was in a poisonous 
Boa, in which three ordinary teeth are found placed singularly in the upper jaw: and this ano¬ 
maly, as it prevented my making alteration in transcribing my own original descriptions, has 
led me to wish that the common teeth should be particularly attended to, in the future exami¬ 
nation of Indian serpents. 
