10 



The Tail and 

 its Uses, 



Shape of 

 Body and 

 Lateral 

 Keels 



The Heads 

 and Head- 

 Shields 



The tail plays no part in the locomotion of 

 the snake, but helps to steer its body, and is useful 

 as a prehensile organ in the case of Tree-Snakes. 



When moving fast the snake lashes itself along 

 the ground in a succession of curves. This enables 

 it to take a hold of the ground with the outer 

 portions of the ventrals, which, gripping the ground 

 better than the central portions, enable the snake 

 to move faster. The tail again comes in useful in 

 assisting the lateral undulations of the snake. 



It is noticeable that in certain fast-moving 

 snakes, such as Zamenis, Dendrophis, and Dryophis 

 (the Rat-snake, Copper Tree-snake, and Whip- 

 snake), the tail is long in comparison with the 

 length of the body, while in slow-moving snakes, 

 such as the families Uropeltidse, Boidse, and 

 Viperidse, the tail is short. 



Certain snakes, the Dipsadinse and the Tri- 

 meresuri, vibrate their tales when irritated. This 

 is in some way explainable in the Trimeresuri, as 

 they belong to the same sub-family (Crotalinse) as 

 the Rattlesnake, but this does not explain the 

 habit in the Dipsadinae. This peculiarity is also 

 noticeable in other snakes, mostly Tree-snakes, but 

 in not nearly so marked a degree. 



Snakes may have cylindrical or compressed 

 bodies. The former are most noticeable among 

 Earth-snakes (Uropeltidse, Xenopeltidse, etc.) and 

 the latter among Tree-snakes (Dipsadinae). Among 

 certain Tree-snakes lateral keels are to be found ; 

 that is, they have their outer rows of scales very 

 much enlarged, and as broad as the ventrals. This 

 is especially noticeable in the different varieties of 

 Dendrophis. 



The heads of snakes vary very considerably, 

 and, together with the shields on them, form the 

 most important factor in the identification of 

 snakes. 



