48 
ROOM X. 
Nat. Hist. 
which live on the ground and take to the water for pro= 
tection, or to catch their food, have generally a cylindri¬ 
cal form, and a tail scarcely so long as the body; while 
those which live the greater part of their life on trees, 
and are thence called Tree-Snakes (Dendrophis), 
are generally very long and slender, and the scales on 
the sides of the back usually narrow, and longer than 
those on the dorsal line: some of the Tree-Snakes 
have the end of the muzzle lengthened out into an acute 
appendage (Passerita). 
The Bull-headed Snakes (Dipsas) resemble the 
Tree-Snakes in form, but the head is short and broad, 
the body compressed, and the latter has a series of 
larger scales down the back. In this group the fangs 
are most commonly found intermingled with the teeth, 
in which character they agree with the Cerberi (Homo- 
lopsisJ 9 which are easily distinguished from all the 
other snakes by the head being scaly, with a few small 
plates over the face and between the eyes. 
The Boas have usually a short body, with narrow 
plates on the abdomen, and a short conical tail, fur¬ 
nished with two short crooked spurs at its base. These 
spurs have lately been shewn to be analogous to the 
hinder legs of other reptiles. The Boas are not venom¬ 
ous ; they kill their prey by crushing it between the 
folds of the body, generally at the same time twisting 
the end of the tail round a tree, in order to increase 
their power. 
The American species (Boa) have only a single row 
of plates beneath the tail; they vary greatly in the 
structure of the scales on the head and lips. 
Some of the Indian species, as the Netted Boa (Boa 
regia), have a single series of plates, whilst most of the 
other species have two rows (Python); as the Javan 
Boa (Coluber javanicus), and the Tiger Boa (Coluber 
boceformis). The Eryx differs from the other Boas in 
having a cylindrical body, a very short tail, and the 
head covered with scales similar to those of the back. 
Cuvier 
