22 



THE SNAKES OF SOUTH AFRICA. 



opposite side are brought parallel with the other set, dragging up 

 the hinder part of the body, and propelhng the upper or anterior 

 part. All tliis is done so smoothly and equally that the snake 

 crawls with the greatest ease, and moreover is exceedingly 

 graceful in its movements. A snake cannot crawl upon a perfectly 



(1) 



Fig. 13. — I. A snake crawls over the ground like this, propelled by its abdominal shields 



the tips of which grip uneven surfaces. 

 2. The erroneously popular idea of how snakes progress over the ground. 



smooth surface, such as a sheet of polished plate glass, it can 

 only succeed in wriggling in a random sort of way. The scales 

 of snakes partly o\'erlap each other. The abdominal sliields can 

 be partially raised bj' certain muscular attachments. 



The male snake has two sex organs. These lie in cavities in 

 each side of the base of the tail. When protruded they turn 

 inside out, and erection is accomplished by a flow of blood into 

 them. The female usually has two vaginal cavities. 



The Teeth. 



Snakes' teeth are recurved ; that is, they are curved inwards 

 towards the throat. Non-venomous snakes, with the exception 

 of the blind burrowing snakes, have two rows of small teeth in 

 the upper jaw, and one row in the lower jaw. The teeth are not 

 set in sockets in the jaw, but are cemented to the bone. If, on 

 examination, these teeth be found to be all solid, without any 

 trace of grooving, then the snake is certain to be of a non- venomous 

 species. But in a great number of snakes with two rows of 

 upper teeth it will be found that one, two, and even three of the 

 teeth in the outer row, usually about half-way back in the jaw, 



