X 



1891 



,i; ] PROCEEDINGS OF TlIK NATIONAL MLSEUM. fi87 



form a compact generic division. Dr. Cones has inoposed to separate 

 the C. cerastes as tyi)e of a separate genns distin^^nished by the prolon- 

 gation of the free border of the snperciliary plate into a hondike pnj- 

 cess. Were this process distinctly articnlated at th(^ base from the 

 superciliary plate, as is the (;ase in the viperine ;;enns Cerastes, we 

 should be compelled to adopt su(!h a division ; but at present I do not 

 seethe way to separate it, especially as the jjrocess is otten but little 

 l)ronounced. I have also proposed a generic division tor the C. IcpiduM 

 based on the single nasal plate, but the plate is sometimes divided in 

 part, and for the present I do not adopt the division nv at least until I 

 can see more specimens of the species. 



The origin of the curious epidermal structure at the end of tlie tail 

 known as the rattle is as yet a subject of si)eculation only. We have, 

 however, so many nuliments of it in other generic divisions of the Cro 

 talid;e that its origin from soaie of these is evident, and that it oc- 

 curred at no very late period of geologic time is i)robable. The terminal 

 caudal vertebne are coiisitied and compressed and expanded into a 

 vertical body which enters the tirst or basal button of the rattle. Snch 

 a modilication is found in a rudimental condition in the genus Lachesis, 

 where it is covered by a simple horny sheath, grooved at the sides. In 

 Crotaloi)horus the rattle is of absolutely and relatively small size, auil 

 here we can see the beginnings of the segmentation ami inllationof the 

 joints, which constitutes the i)erfected structure. The physiology of for- 

 mation of these segments has not been studied as yet, but the general 

 the( ry of the origin of the entire stricture is probably the same in this 

 case as in others in the animal kingdom. The violent vibrations into 

 which most snakes thiow their tails when excited has deternntu-d lui- 

 tritive processes to its extremity and produced the excessive growth. 



The species of this genus are of rather sluggish moviMnents, and are 

 not quick to bite, unless trodden on. They throw the body into a coil 

 and sound the rattle, giving a sigmoid llexure to the anterior p;ut of 

 the body, on which the head is poiseil with open moutii ready for 

 a(;tion. At this time drops of the [misonous saliva fall from the fangs, 

 aiul by a violent expulsion of air from the lungs are thrown at their 

 enemy. In the act of l)iting the movement isthreefohl. First, there is 

 the spring of the binly, whicli never exceeds two-thirds of its length ; 

 secoml, the bite proper, caused by the seizing by the Jaws; and, third, 

 the clutch with the fangs themselves, which are moved fn-ely backwards 

 and forwards by the llexor and extensor nniscles of the maxillary bono 

 on tlie prelVont.d as a lixed i»oiiit. This grasping movement may Im 

 observcil in Crotali when very niin-h exirited and anxious to bite, ami 

 may be performed by the snake's heail wlien severed from tiie body. I 

 had a narrow escape from being bitt«'n in this way by the head of a 

 Crotnlus molossiis, which was attached to the body ity skm oidy. 



Rattlesnakes live in all kinds of ground, but natnr;dly persist longest 

 in rocky regions, where tliey have abundant places of concealment. 



