STRUCTURE OF SNAKES 



707 



the maxilla is rotated on its lachrymal joint, the fangs borne 

 by the maxilla are erected into a vertical position, the poison 

 gland is compressed by a muscle, and the venom is forced 

 through the fang. 



Some of the peculiarities in the internal organs of Ophidia 

 may be connected with the elongated and narrow shape of 

 the body. Thus one lung, usually the left, is always sm.aller 



PMX 



ART 



Fig. 417. — Side view of the skull of a poisonous snake. — 



From a Specimen. 



PMX., Premaxilla ; MX., maxilla ; F., one of the fangs ; PL., 

 palatine reaching to maxilla ; PT., pterygoid ; O.T., os trans- 

 versum from pterygoid to maxilla ; D., dentary ; A ., angular ; 

 ART., articular ; Q., movable quadrate ; SQ., squamosal ; PER., 

 periotic ; PA., parietal; P.P., post-frontal; 0., orbit, with the 

 frontal above ; L., lachrymal, fused to the pre-frontal (PRE.) ; 

 the maxilla [MX.) moves on the lachrymal ; N., nasal. 



than its neighbour, or only one is developed ; the liver is 

 much elongated ; the kidneys are not opposite one another. 

 The poison is useful in defence, and in killing the prey, 

 which is always swallowed whole. It is interesting to notice 

 a recent discovery, requiring amplification, that the bile of 

 a poisonous snake is an antidote to its venom. 



The British adder [Pelias berus) is viviparous, and so are a few 

 others. The great majority are oviparous, but confinement and 

 abnormal conditions may make oviparous forms, like the Boa con- 

 strictor and the British grass-snake (Tropidonotus natrix), viviparous. 

 The female python incubates its eggs. 



