OF THE INTEGUMENTS. 
75 
Tortrix scytale. They exist even in many serpents whose 
heads are deprived of plates, and are replaced in others by 
a circle of little scales. 
Two pairs of plates, the anterior and posterior Fron- 
tals, cover, in the greatest number of Ophidians, the upper 
part of the muzzle. Their form is, in a great measure, de- 
termined by the lateral edges of that part, so as to be very 
narrow in the Dryiophis, and wide in the Dipsas, &c. 
The anterior are smaller than the posterior : they are 
sometimes very small, as in many species of the genera 
Lycodon, Dipsas, Elaps, Homalopsis, &c. ; in some of the 
latter genus they are reduced to a single pair, wedged in 
between or behind the nasals, which occupy their place ; 
in the Hydrophis, the Tortrix, and the true Calamaria, 
they totally disappear, and we then see but a single pair 
of frontals. Their number, on the other hand, is in- 
creased in other Ophidians, as in several Boas, the Trigo- 
nocephalus hypnale, the Heterodon, and the Hydrophis 
colubrina ; in other Boas, they are replaced by small 
plates of an irregular figure, which are not distinguishable 
from the scales. The modifications which these plates 
undergo in the diverse races of Ophidians are numerous, 
as may be seen in examining the figures in our plates. 
The muzzle of serpents is always terminated by a plate 
more or less large, and always grooved below, to receive 
the extremity of the lower jaw. The form of this Rostral 
plate varies according to its use. It is most usually 
pentagonal ; the size is determined by that of the muzzle ; 
it is broad and very convex in most Ophidians ; in others, 
as the Heterodon, the Naja haemachates, the Eryx, many 
Trigonocephali, &c., it is obliquely truncated down- 
wards ; in the Dryiophis, it enters into the moveable ap- 
pendix, with which the snout of that animal is pro- 
vided. 
The Labials are those plates which garnish the edges of 
the lips ; they are most frequently disposed in a single 
row, sometimes in two or more rows, or rather, we find 
several supernumerary plates, inserted between the labial 
plates : this takes place in the Hydrophis, in several Ho- 
