. LECTURE VII. 
35 
the general pattern or disposition of the colours is 
- perhaps a more certain criterion, though confessed 
to be liable to alteration. 
One of the most singular properties of the 
Serpent tribe is that of casting their skin from 
time to time. When this operation takes place, 
so complete is the spoil or cast-skin that even the 
external coat of the eyes themselves makes a part 
of it. The distinction of Serpents into poisonous 
and innoxious can only be known by an accurate 
inspection of the teeth; the fangs or poisonous 
teeth being always of a tubular structure, and fur- 
nished with a small hole or slit near the tip : they 
are rooted, into a particular bone, so jointed to* 
the remainder of the jaw on each side, as to 
.permit the fangs or poisoning teeth to be raised 
or depressed at the pleasure of the animal. Above 
the root of each is a glandular reservoir of poison, 
which in the act of biting is pressed into the 
tube . of the tooth, and discharged into the wound 
-through the hole near the tip. The fangs are ge- 
-nerally single on each side ; sometimes double or 
.treble, and in general there are small or young 
Tangs situated at the base of the larger ones, ready 
to, grow up and supply their place when lost by 
