66 
room x. and a tail, scarcely so long as the body ; while 
those that live the greater part of their life on 
trees, and thence called Tree-Snakes (Den- 
drophis ), are generally very long and slender, 
and the scales of the side of their back are 
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 body is com¬ 
pressed, and the head short and broad, and with 
a series of larger scales down the back. In this 
group the fangs are most commonly found in¬ 
termingled with the teeth, in which character 
they agree with the Cerebi ( Homolopsis ), 
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 coni¬ 
cal tail, furnished 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 venomous; they 
kill their prey by crushing it between the folds 
of their body, generally at the same time 
twisting the end of their tail round a tree, in 
order to increase their power. 
The 
