Crotalus triseriatus—Spotted rattler. 
Mountains of southeastern Arizona, and through the central plateau 
of Mexico. 
Crotalus willardi—Ridge-nosed rattlesnake. 
Santa Rita Mountain region, Arizona, and northern Mexico .: 
POISON APPARATUS OF VENOMOUS SNAKES 
The fluid, or venom, is injected into the snake's victim by means 
of specialized teeth on the maxillary bone of the upper jaw, which differ 
from normal reptilian teeth in having a groove, or canal, from base to 
apexes) (nese venompianes) am whe Ganigevous ae are large and readily 
Odscwved. The canelis)/ol the fengs ane fed with fluad through ducts trom 
the poison giands. Venom does not flow freely except when the snake is 
actually striking, for the end of the duct, which is not in contact with 
the base of the fang, is normally compressed by & sheath, or fold of mu-— 
cous membrane. A rattlesnake may open its mouth to the fullest extent 
yet may or may not erect the fangs. The snake apparently hes perfect 
control: over ats fangs, raising or depressing them at will, The venom 
is injected by the combined action of several muscles, which open the 
mouth, erect the fangs, compress the poison glands, and thus force the 
venomous fluid through the connecting duct into and through the fangs 
in the brief space of time in which the snake strikes its victim. 
At the.end of a stroke the fangs of a poisonous snake are quickly 
withdrawn from the flesh; the whole action is the work of an instent. 
Unless the snakes strikes agein, the mouth closes as the fangs-fold 
back, mechanical compression constricts the excretory duct, and pressure 
is relieved from the poison glands by relaxation of the enveloping mus-— 
cles. A poisonous snake often miscalculates the distance of the object 
au) whtichiwait) 1s striking... fm case tne object,is too close, the fangs 
are not fully erect when the snake strikes and hence do not penetrate. 
Gonversely, if the thing struck at is beyond rcach, the whole stroke 
may be completed without touching the object of attack. In this case it 
may happen that the venom is projected several feet, an action that has 
given rise to repeated accounts of our poisonous angles spitting venom. 
In human beings the bite of a venomous snake is usually followed 
by painful symptoms and occasionally by death. Other animals are af— 
feeved in various ways. The hog, for example, has a degree of immunity 
from the bite of venomous snakes, because of its thick skin and pro-— 
tectiang Layer of fat. 
Poison Fangs 
Though the fangs of our crotaline venomous snakes are shed fre- 
Quicnibili Wat Camnoy be, Said) thay \they, are shed periodically. On eacn 
side of the upper jaw there is a hollow or grooved poison fang firmly 
ankylosed to the maxillary bone. This pair of functional fangs is 
supplemented by several pairs of smailer tceth growing loosely in the 
flesh and buried in the soft sheath of the gum. When from any cause 
one of the large fangs is broken off, the reserve fang nearest to it 
soon moves over in.its place, grows fast to the maxillary bone, and 
becomes the functional poison fang. In case of accident to either of 
the fangs in use, there is always a reserve fang ready to replace it. 
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