Biology Reference
In-Depth Information
Plate 2.5
Eastern brown snake (
Pseudonaja textilis
).
Pseudonaja textilis
and its congener,
P. nuchalis
(western brown snake), are the most medically important snakes in Australia.
Pseudonaja textilis
is also found in West Papua and Papua New Guinea, and has a notorious
reputation. The color morphology of this elapid is widely variable from all shades of brown to
black with multiple tinted color tones (ochre, rust, yellow). They have small fangs, but possess
highly toxic venom containing the most potent snake venom toxin characterized to date
(textilotoxin, a presynaptic multimeric neurotoxin, the murine i.p. LD50 is 0.001 mg/kg)
as well as other neurotoxins (e.g., pseudonajatoxin A, a postsynaptic neurotoxin). However,
human envenomation typically consists of severe coagulopathy (as in hazard level 1
colubrids), and very rarely includes neurotoxic effects. Envenomation may result in rapid
systemic complications (seizures, cardiac effects, collapse, and arrest). However, some 80% of
bites result in no envenomation (“dry bites”).
Photo copyright to David A. Warrell.
as this may stimulate increased secretion via secondary anatomical influences (see
later). Duvernoy's secretion yields from a variety of non-front-fanged colubroid taxa
were reviewed by Weinstein and Kardong (1994) and are selectively reviewed later
(also see Appendix B).
In view of the lack of muscular compression, release of Duvernoy's secretion
appears to result primarily from autonomic stimulation (Rosenberg, 1992). However,
as the gland tightly adheres to the overlying skin and the quadratomaxillary ligament
runs from the posterior aspect of the gland and inserts on the distal end of the quad-
rate, contraction of jaw adductors may contribute to gland pressurization (Weinstein
et al., 2010). Some observations suggest that in other species there may be additional
(secondary) sources of pressurization due to anatomical relationships between “venom
ducts” and surrounding structures (Fry et al., 2008). Fry et al. (2008) suggested that in
cross-sectional analyses, the “venom duct” of some taxa was more crenated and was
surrounded by concentric layers of connective tissue suggestive of pressure regulation.
