2538 SCALED REPTILES 



placed in a vertical plane are altogether erroneous. In conformity with their elon- 

 gated bodies, the internal organs of snakes are long and narrow; and it is remarkable 

 that, as a rule, only one of the lungs is developed. 



Resembling the other members of the order to which they belong in 

 that their teeth are never implanted in distinct sockets or grooves, 

 snakes exhibit some considerable degree of variation with regard to the number 

 and structure of their teeth. In the ordinary harmless forms there are generally 

 two rows of short, slender, and sharply-pointed teeth in the upper jaw, the inner- 

 most of which are attached to the bones of the palate, while the lower jaw carries 

 only a single row of such weapons. One or two of the outer row of upper teeth, 

 either at the front or back of the series, may, however, be enlarged beyond the 

 rest, and grooved or tubular; and it is probable that all snakes with such a dental 

 armature are more or less venomous. Some most deadly poisonous serpents have, 

 on the other hand, a type of dentition of their own; and there is no doubt that all 

 snakes with teeth of this nature are extremely venomous. In such snakes the 

 fore part of the very short maxillary bone of each side of the upper jaw is armed 

 with an elongated tubular tooth, which ordinarily lies nearly flat on the surface of 

 the palate, but can be erected, by a peculiar mechanism of the bones, when the 

 jaws are opened. Although in this group the poison fangs are always tubular, in 

 some of the other venomous serpents they are merely grooved for the conveyance 

 of the venom from the secreting gland; but there is a transition between the two 

 types, as the closed tube is formed merely by the edges of the groove being elevated 

 until they unite in the middle line. In poisonous snakes, on each side of the upper 

 jaw, below and behind the eye, is situated the poison gland merely an ultra de- 

 velopment of an ordinary salivary gland, these glands in some cases being so 

 developed as to extend far back along the sides of the body. The gland is over- 

 lain by a layer of muscles, for the purpose of forcing the secretion into the tooth 

 (the base of which is always open) when required, this action always taking place 

 when the snake opens its mouth to bite. The poison then flows along the channel 

 or tube of the tooth, and is discharged at its extremity into the wound. Consider- 

 able force is used in the emission of the poison, as, when a snake is irritated, the 

 fluid may be seen to spurt for some distance from its point of discharge. In some 

 of the less specialized poisonous snakes, the venom tooth, which has an open chan- 

 nel, is not greatly longer than the others, and is placed nearly vertically when 

 the mouth is closed. Although the poison teeth are commonly regarded as purely 

 defensive weapons, their chief use is for the destruction of the prey of their owners, 

 which is always killed before being swallowed. The venom tooth of the more 

 specialized poisonous snakes is exceedingly likely to be broken off during use; but 

 to take its place there are always several others lying on the gum behind it in differ- 

 ent stages of development. 



Before the doctrine of parallelism in development received from 

 Harmless and .. . 



p . naturalists the attention it undoubtedly merits, snakes were generally 



Snakes divided into harmless and poisonous groups; but since we have 



become better acquainted with that important factor in evolution, it 



has been recognized that such a distinction is a purely artificial one, and has noth- 



