24 PRESIDENT'S ADDRESS. 



peculiarities of Ophidia, as compared to Lacertilia, is the 

 absence of any solid union between the rami of the mandibles, 

 the two being connected by an elastic ligament, which allows 

 the animal to dilate the mouth and swallow a much larger prey 

 than it could otherwise admit into it. No Snake has an ear 

 opening. The absence of a sternum gives a remarkable facility 

 of movement to the ribs, which are terminated by a tapering 

 cartilage, attached to the abdomen by a muscular connection ; 

 by this mechanism the animal is able to glide rapidly along the 

 ground upon the ends of the ribs, aided by the extreme mobility 

 of the vertebral column, and the raising and depression of the 

 abdominal scutes. The teeth, which are conical and recurved 

 and anchylosed to the jaw, are used rather for killing and holding 

 their prey than for mastication. The mandible has the power of 

 independent motion by the alternate action of intrusion and 

 protrusion, by which the prey is drawn into the gullet. It is 

 probable that all Snakes with grooved teeth will prove to be 

 poisonous to a greater or less degree, as the grooves must have 

 some function ; these teeth are not truly perforated, but the edges 

 are folded over so as to form a duct to carry the poisonous 

 secretion ; when the edges meet and coalesce, the fang may be 

 said to be perforated, and when they nearly approach each other, 

 a channelled duct results. The Order comprises Colubridae, 

 Pythonidae, Boidae, Erycidae, Elapidae (venomous, includes 

 Cobras), Crotalidae (includes Rattlesnakes), and Viperidae. Colu- 

 bridae form the bulk of the Order, and are represented in. all 

 the temperate and tropical regions of the world, with the 

 exception of Australia. Our knowledge of fossil Snakes is 

 very limited ; their imperfect preservation makes it difficult to 

 systematically determine them. With the exception of one 

 doubtful species (Cimo/iophis from the Lower Chalk, Isle D'Aix, 

 Charante, France) all are Tertiary or Post-tertiary. The next 

 earliest genus is Helagrus from the Lower Eocene of North 

 America ; it is the oldest known Ophidian fossil of the New 

 World. The African types as known at present predominate, 

 belonging mostly to the Aglj'phedontia, which are harmless. 



