COUES AND YAREOW ON HERPETOLOGY. 267 



the spheno-palatines contract, and the fangs spring into position, throw- 

 ing off the sheath as they leap forward. With delivery of the blow and 

 l^euetration of the fangs, the lower jaw closes forcibly, the muscle that 

 executes this movement causing simultaneously a gush of veuom 

 through the tubular tooth into the wound. There are also some second- 

 ary actions, though all occur at nearly the same instant. The mouth 

 fixed at the wound drags upon it with the whole weight of the snake's 

 body. This dragging motion is accompanied by contraction of the 

 ectopterygoid and spheuo-palatine muscles, which ordinarily fold back 

 the tooth; but the fang being at this moment engaged in the flesh, the 

 action of the muscles only causes it to bury itself deeper, and thus en- 

 large the puncture. The train of action seems to be, the reaching of 

 the object, the blow, the penetration, the injection of the poison, and 

 the enlargement of the wound. These actions completed, the serpent 

 loosens its hold by opening the jaws, and disengages itself, sometimes 

 not without difficulty, especially when the bitten part is small and the 

 numerous small teeth have caught. The head is withdrawn, the fangs 

 folded, the mouth closed, and the former coiled attitude of passive 

 defense is resumed. 



These remarks api)ly in substance to other species as well as to the 

 one now under special consideration. Upward of eighteen species, not 

 counting Ancisfrodon, are described as inhabitants of the United States, 

 nearly all of which occur in the West and Southwest. Our rattlesnakes 

 fall in two genera, Crotalus and Caudisona, readily distinguished by the 

 scutellation of the head. In the former, the top of the head is covered 

 with a large number of small asymmetrical scales like those on the body ; 

 in Gaudisona, the same region is shielded by a definite small number of 

 large flat places symmetrically disposed. Crotalus horridns is a most 

 widely dispersed species of Eastern JSTorth America, the only other spe- 

 cies of the same portion of the continent being G. adamanteus, the "Dia- 

 mond" rattlesnake of the South Atlantic and Gulf States. With the 

 latter is found associated a species of Gaudisona, namely, G. miliarius, 

 the small spotted rattlesnake; but the best known species of the latter 

 genus is Gaudisona t€rgemi7ius, the common " Massasauga" of the interior 

 States and of the Plains. Texas, New Mexico, and Arizona furnish the 

 largest number of species. 



Grotalus confiuentus is a species of more and general distribution in 

 the West, from the Mexican to the British boundary, and on both sides 

 of the Eocky Mountains. It is associated in some parts with the 

 Massasauga, but in other regions, as in the one now under considera- 

 tion, it is the only known representative of its family. It appears to 

 be particularly numerous in the region of the Yellowstone, where, 

 according to Mr. Allen, it was estimated that two thousand were killed 

 during the expedition of 1872. Farther northward, it is less abundant, 

 though fairly to be considered common in the region of the Upper Mis- 

 souri and Milk Eiver and some of their northern tributaries. Along the 



