31 



or truncated behind. In front of the vertical are two pairs 

 of shields, the "posterior frontals more or less square, and 

 the anterior frontals of similar form, but smaller and liable 

 to encroachment in front and at the sides. On either side 

 of the vertical are the two supraciliaries, of regular and 

 crescentic shape, shading the eyes. They complete the oval 

 of the crown, covering the space between the postfrontal 

 and prefrontal bones. 



These four pairs of shields with their centre, the vertical, 

 form the crown ; the other shields are on the sides of the 

 face. 



The muzzle is covered by a convex triangular shield, the 

 rostral, which often extends up a little way between the 

 anterior frontals ; it is broad at its base with a slight chink 

 in the middle for the exit of the tongue without the mouth 

 being opened. 



Behind the rostral on either side are two series of shields, 

 one above the other ; the lower series is that of the labials, 

 (upper) varying ordinarily from five to nine in number, and 

 increasinof in size from before hindward. One or more of 

 them enter the orbit when there is no subocular. In the 

 Pythonidoe, the labials and rostral are indented with deep 

 pits in the shape of a comma. 



The shields between the labials and the crown on either 

 side are the nasals, the loreal, the oculars, and the tem- 

 porals. The nasal is sometimes single, being pierced by the 

 nostril, but more frequently there are two nasals with the 

 nostril between them. In the water-snakes, Hoonalopsidce 

 and HydrophidcB, where the nostrils are superior, the nasals 

 of either side are often contiguous, excluding the anterior 

 frontals from contact with the rostral. 



The loreal (frenale) is absent in the venomous snakes ; 

 and in some harmless snakes, the Calamaridce, Tetragono- 

 soma, Xenopeltis and several genera of tree-snakes it is 



