2 
INTRODUCTORY LETTER. 
rected my researches to the class of Eeptiles. I commenced 
by representing in accurate designs the most interesting 
species of this little understood class of beings, and it is 
thus that by degrees was formed a series of anatomical 
and zoological drawings, one part of which I now publish, 
and shall cause the rest to follow when the numerous dif- 
ficulties that at present impede the publication of my re- 
searches shall have been wholly removed. 
I have abridged in my book all the observations which 
I have been able to make in Ophiology. Yet, the state in 
which this part of science exists has constrained me to de- 
viate in many respects from my original plan, and to defer 
the publication of the anatomical researches, which are 
the basis of my labours. How could my readers, for in- 
stance, have comprehended me if I had spoken to them of 
the numerous new species, the discovery of which is due 
to our travellers ? How could they explore the way through 
systems containing such a vast number of species, often 
purely nominal or more than once introduced ? What 
work could we recommend to serve as a guide through this 
labyrinth ? I do not know any such. 
These reasons, joined to several others, have decided 
me on giving to my book the form under which it now ap- 
pears. In the mean time, in conceiving this new plan, it 
presented diificulties similar to those to which I have al- 
luded. To what figures could I refer to complete my de- 
scriptions ; and how few naturalists can even consult those 
expensive works in which they are contained ? Besides, 
110 study offers more difficulties than the comparison of 
different species of serpents, — animals which so nearly re- 
semble each other in the form of their bodies, that one is 
often obliged to have recourse to the structure of the head, 
to obtain for them distinctive characters. 
These motives have induced me to delineate on the same 
plate the figures of all the species of each genus, or, at least, 
those of the most remarkable. On comparing these por- 
traits, one will readily be able to seize the peculiar phy- 
siognomy of each, and thus to distinguish nearly allied 
species. 
The word Physiognomy is here used in its ordinary ac- 
