14 VENOMS 
sufficient to retain the prey and to cause it to pass from front to 
rear towards the cesophagus, by a series of alternate antero-posterior 
movements and analogous lateral ones. By means of these move- 
ments, which are participated in by the upper and lower maxillary 
bones, the palatines, mandibles or inter-maxillaries, and the ptery- 
goids, the animal in a manner draws itself over its prey like a 
glove, since the arrangement of its dentition does not admit of 
mastication. 
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F1G. 13.—ARRANGEMENT OF THE SCALES OF THE HEAD IN ONE OF 
tHE Non-porsonous Colubride (Ptyas mucosus). (After Sir Joseph Fayrer.) 
A, Rostral scale; B, anterior frontals; B', posterior frontals ; ©, vertical; D, occipi- 
tals; E, supra-ciliaries; F, temporals; L, M, nasals ; N, loreals, or frenals; 0, anterior 
oculars, or præ-orbitals; P, posterior oculars, or post-orbitals; Q, supra-labials; G, 
median infra-labial; HH, lateral infra-labials ; 1k, mentals. 
; 
The enormous extensile power of the mouth and cesophagus 
thus enables snakes to swallow animals, the size of which is several 
times in excess of their own diameter. 
Deglutition is slow and painful, but the gastric and intestinal 
juices are so speedy in action, that the digestion of the most 
