Biology Reference
In-Depth Information
envenomation very late (up to 24 h after the bite), present with substantial delay after
a bite from one of these species, and exhibit coagulopathy without any outwardly
concerning signs on examination.
4.3.1.1 Overview of the Duvernoy's Gland and Associated Dentition of
D. typus
and
Thelotornis
spp.
The medical risks from these snakes are associated with their notably enlarged and
relatively numerous posterior, deeply grooved maxillary teeth (
Plates 2.15, Plate
4.20D-J, and 4.56C, H-K
), markedly serous glands (with some limited muscle
attachment), and highly toxic venoms. Consistent with the arboreal habits of these
snakes, their prey often includes lizards and birds (see
Table 4.2
for examples). A
Fischer's chameleon (
Chameleo fischeri
) seized by a
T. usambaricus
in northern
Tanzania succumbed within a few minutes, turning a deep black color just prior
to death (SAW, personal observations). The Duvernoy's glands of this tribe dis-
play size variability that may have some correlation with their medical importance.
Thrasops
spp. and
Rhamnophis
spp. possess relatively small glands. The gland size
is increased in
Thelotornis
spp. and
Xyelodontophis
and reaches an apex in
D. typus
(Broadley and Wallach, 2002). In his histological study of oral glands of approxi-
mately 180 colubrid species, Taub (1967) emphasized the distinctive character of the
D. typus
Duvernoy's gland as these glands were readily distinguished from all other
non-front-fanged colubroid glands that were examined. Although he reported vari-
ability in the thickness of the gland capsule (one specimen, CM #6340, had a thin
capsule; the other, AMT No. 5, had a “very heavy, thick” capsule), he observed sev-
eral features that highlighted the active secretory function of the
D. typus
Duvernoy's
gland. The glands had: “very many” trabeculae of variable thickness;
90% of
tubules had lumenae; mucous cells and mucous supralabial glands were absent; also,
high vascularity was noted. The gland substance was composed of either colum-
nar or cuboidal cells (Taub, 1967). He similarly described the Duvernoy's gland of
T. kirtlandii
as having: a “heavy thick” capsule; with many thick trabeculae;
90%
of tubules with a lumen; intraglandular mucous cells as well as a supralabial mucous
gland were absent (Taub, 1967). The highly tubuloacinous gland of
D. typus
exhib-
its extensive folding. This provides some limited space for venom storage, thus con-
stituting a minimal cisternae (Broadley and Wallach, 2002; Weinstein et al., 2010).
Taub (1967) noted the lobular evaginations and invaginations of the
D. typus
gland
that contributed to the substantial secretory and storage space, and compared these to
the “folding” (rugae) present in the mammalian gall bladder.
The multiple, enlarged posterior maxillary teeth of
D. typus
possess a deep groove
that is restricted to between approximately 50% and 65% of the tooth length (see
Plate 4.20H-J
), while those of
T. capensis
have a deep groove that runs most of the
tooths' length (Jackson and Fritts, 1995; Fry et al., 2008). The multiple enlarged pos-
terior maxillary teeth of
T. kirtlandii
have similar deep grooves that run almost the
entire length of the teeth (
Plate 4.56H-K
). Meier (1981) described blade-like modifi-
cations of the surface of these teeth. This modified surface presumably facilitates the
introduction of venom through the integument of prey or human victim.
Thelotornis
