Chapter V 



OPHIDIA— SNAKES 



As previously mentioned when dealing with the lizards, 

 the chief peculiarity of snakes resides in the absence of a 

 solid union between the branches of the lower jaw, the two 

 halves being connected by an elastic ligament, allowing 

 these creatures to dilate their mouths to a very considerable 

 extent, and which, in combination with the mobility of 

 the upper jaw, and the movably attached ribs, enables 

 them to swallow prey of a much larger size than would 

 otherwise be possible. The eyes, which may be rudi- 

 mentary or large, with a round pupil in the case of diurnal 

 species, and a vertical, or occasionally a horizontal one, in 

 the case of the more nocturnal, are entirely devoid of 

 movable lids, the eyeball being covered with a transparent 

 disk. No snake has ear-openings, and the sense of hearing 

 is consequently only feebly developed. Although rudi- 

 ments of hind limbs are present in a few families, snakes 

 are practically limbless, moving their elongate bodies by 

 lateral undulations. The ribs have often been stated to 

 be the chief agent of progression, but when we consider 

 the ease and rapidity with which limbless lizards enclosed 

 in a bony armour are able to move, we cannot help thinking 



that their importance has been somewhat exaggerated, 



96 



