198 
SNAKES. 
The Colubrine Snakes. 
Family COLUBHID^E. 
The skulls of the remaining snakes are markedly distinguished from those 
of the foregoing by the total absence in the lower jaw of the bone known as the 
coronoid; while in all cases a supratemporal is present on the upper surface of the 
skull. The present family, which includes by far the great majority of the species 
of the suborder, and comprises both harmless and noxious kinds, is specially 
distinguished from those to be mentioned later on by the circumstance that in 
the skull the upper jawbone, or maxilla, is fixed in a horizontal position, and 
also that the pterygoids reach either to the quadrate-bone or the lower jaw. 
Before coming to the Colubrine family it should, however, be mentioned 
that there is one remarkable snake {Xenopeltis unicolor), from South-Eastern 
Asia, retaining in the structure of its skull traces of affinities with the boas and 
pythons. This affinity is displayed by the fact that the prefrontal bone, which 
lies immediately behind the nasal aperture of each side, is of large size, and 
extends forwards and inwards to articulate with the nasal bone in the same 
manner as the boas. Accordingly, this snake is regarded as the representative of 
a distinct family (Xenopeltidai), which is considered to have originated from the 
Boidce quite independently of the Colubrines. 
From Xenopeltis the Colubrines are distinguished by the small size of the 
prefrontal bone of each side, which articulates merely to the outer front angle of 
the frontal bone without any contact with the nasal bone. In such a large group 
it is highly important to have some means of division into subgroups of higher 
value than genera; and, according to the modern classification, three such serial 
divisions may be indicated by the characters of the teeth. The first and most 
primitive of these series, which may be termed the solid-toothed colubrines 
(. Aglypha ), is characterised by the whole of the teeth being solid, without any 
trace of grooves, all its representatives being harmless, O 11 the other hand, in the 
second series or hind-fanged colubrines ( Opisthoglypha ), one or more of the hinder 
teeth of the upper jaw are grooved; while in the third series or front-fanged 
colubrines ( Proteroglyplia ) the front teeth of the upper jaw are grooved or tubular. 
Of the last series the whole of the members are poisonous, while many of those 
of the second are noxious in a minor degree. All these three sections contain 
species adapted to particular modes of life, so that we may have two or three 
snakes which, while externally very similar, are only distantly allied to one another. 
The Javan wart-snake (Acrochordus javanicus) may be taken 
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as a well-known representative of the first, or acrochordine subfamily 
of the solid-toothed colubrines, which includes only five genera, distributed over 
South-Eastern Asia and Central America. Unfortunately, the characters distin¬ 
guishing this subfamily from the next are connected with the bones of the skull, 
and cannot therefore be verified without dissection, but in the study of snakes, 
according to the modern system, the student must accustom himself to such 
difficulties. The essential feature of the skull in the present group is the pro¬ 
duction of the postfrontal bone above the cavity of the eye; while, as a secondary 
