Mechanics of venom expulsion in Crotalus, with special reference to the role of the fang sheath

A combination of anatomical and experimental preparations were used to expl ore the function of the venom delivery system in rattlesnakes (Crotalus). T he distal end of the venom duct is compressed near the point where it empti es into the venom chamber, a space surrounding the fang defined by the fang sheath. Within the venom chamber, the inner fang membrane lies obliquely o ver the base of the fang at least partially occluding the entrance orifice. When the fang is retracted the combination of the compressed venom duct an d the spatial position of the inner fang membrane serve to inhibit or block venom flow. As the fang is erected beyond approximately 60 degrees (relati ve to the roof of the mouth) localized compression of the fang sheath decre ases the size of the venom chamber, relieves the compressive force from the venom duct, and displaces the inner fang membrane away from the entrance o rifice of the fang. Pressure recordings taken at different locations along the venom delivery system demonstrate that the venom gland produces suction during relaxation of the extrinsic glandular musculature. These findings s uggest that the venom delivery system of Crotalus is both more flexible and more regulated than previously assumed. Anat Ree 264: 415-426,2001. (C) 20 01 Wiley-Liss, Inc.