90 



OUTLINES OF NATURAL HISTORY. 



"quadrate bone" (Latin, quadrattis, four-sided). This 

 bone is directed backwards beliind the base of the skull, 



Fig. 41.— Skull of the Rattlesnake (after DumerU and Bibron). I One-half 

 of the lower jaw, united to the skull by the quadrate bone (5) ; ra Upper 

 jaw carrying the poison-fang ; p Series of teeth upon the palate. 



and owing both to this circumstance and to its mobility, 

 the snake can open its mouth to an extraordinary width, 

 and swallow morsels of comparatively immense size. 



Along the palate above, on each side, is also a row of 

 small conical recurved teeth (/>); but the upper jaws offer 

 the most striking peculiarities. The upper jaw (fig. 41, 

 m) is a short movable bone, so jointed to the skull that it 

 can be raised and depressed at will. Each upper jaw car- 

 ries a great curved tooth, firmly amalgamated with the 

 bone of the jaw, and termed the "poison-fang." The 

 poison-fangs are not only of much greater size than the 

 other teeth, but they are provided with a canal, which 

 opens at the point of the fang in a minute aperture. 

 The canal in the fang communicates above (fig. 42) with 

 the tube or duct leading from a singular organ known as 

 the " poison-gland." This organ (fig. 42, a) is a gland 

 placed beneath and behind the eye, and secreting the 

 peculiar fluid which renders the bite of the snake fatal. 

 When the snake wishes to kill an animal for food, or when 

 attacked by an enemy, it employs these formidable 

 weapons in the following manner : The great poison-fangs 



