SNAKES 97 



although of undoubted use for the purpose of climbing 

 and of slow crawling on rough ground. 



Snakes have their entire head and body covered with 

 scales, the disposition of which are made great use of in 

 their classification ; those of the head may be either large 

 and symmetrical, or small and irregular in shape, and there 

 may be, in addition, erect, horn-like appendages on the 

 snout or over the eyes. The scales of the back, which most 

 frequently overlap and are arranged in oblique transverse 

 series, may be perfectly smooth or provided with keels ; on 

 the undersurfaces they are replaced by broad transverse 

 shields, which are usually disposed singly on the belly and 

 in pairs on the tail. The tongue, which is deeply forked 

 and retractile into a basal sheath, is a highly developed 

 sensory organ, acting as a feeler. The jaws are provided 

 with long, sharply pointed, often needle - like teeth, 

 which are frequently shed, but soon replaced by reserve 

 ones. In the harmless species these are all perfectly 

 smooth and solid, while in the poisonous species they are 

 either grooved or canaliculated, and connected by a duct 

 with a poison gland, situated on each side of the head, 

 behind the eye, but which sometimes is produced along 

 the side of the body. The poison secreted by the gland 

 is conveyed through the duct to the base of the fang 

 through the compression of the temporal muscles, when 

 the snake opens its mouth. Some snakes are able to dis- 

 charge the venom without actually biting, but by shooting 

 the poison from their mouths, often to a considerable 

 distance, such snakes being popularly known as " spitting 

 snakes." 



Although the idea is prevalent that the great majority 



