76 
Olf THE PHYSIOGNOMY OF SEEPENTS. 
malopsis, &c. The number, configuration, and disposition,, 
of these plates are extremely variable ; and the enumera- 
tion of these discrepancies, therefore, enter into the special 
part of my work ; we may, in the mean time, observe, 
that those of the upper lip go on diminishing towards the 
end of the muzzle in most serpents, and the reverse in 
some measure takes place in the lower jaw. It most ge- 
nerally happens that the superior labials form the lower 
border of the eye. 
This organ has its lateral borders furnished with small 
plates, denominated the Oculars. Several Ophidians 
have only a single anterior ocular, while the number 
of the posterior oculars varies from two to four, according 
to the species : sometimes they are prolonged below the 
eye ; and in several serpents, whose heads are covered 
with small scales, they are small, and form a range, sur- 
rounding the whole periphery of the eye. In the Tortrix 
scytale, all the marginal plates of the eye are joined in 
one single piece, in the centre of which that organ is 
placed. 
It rarely happens that the nostrils perforate the Nasal 
plate, without dividing it vertically into two ; this, how- 
ever, takes place in the genera Tortrix, Boa, Elaps, and 
in most of the true venomous snakes ; sometimes even, 
as in the Elaps, the nostrils open just between two plates 
of different forms, the posterior of which may be consi- 
dered as a Frenal. The form of the nasals, and their po- 
sition, undergo considerable modifications in different 
species of Ophidians : in aquatic serpents, those plates 
are usually near the summit of the muzzle, and some- 
times serve the purpose of the superior frontals, as in the 
Hydrophis ; but more usually they occupy the sides of 
the muzzle, touching the rostral plate by their anterior 
edges. 
These are most commonly followed by another plate, 
the Frenal, which extends to the anterior oculars : this 
plate is, however, wanting in a great number of Ophidi- 
ans, while its place is occupied in others by two, three, or 
more plates, of very different extent and form. 
