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and venom glands among many representative venomous colubroids) argues against
this (Jackson, 2003). Also, Duvernoy's glands and venom glands of viperids, elapids,
and atractaspidids all are innervated by the same cranial nerve [maxillary branch (V 2 )
of the trigeminal nerve] (Kochva, 1965; Taub, 1966), and supplied with blood by ves-
sels branching from the internal carotid artery (Kochva, 1965). In Natrix tessellata (dice
water snake, tessellated water snake), the anterior teeth arise from the anterior portion
of the maxillary dental laminae, and the posterior “fang” (which is associated with the
Duvernoy's gland) from the posterior section (Jackson, 2003).
In N. tessellata , Duvernoy's gland is not homologous with the mammalian parotid
gland because it has a different embryonic origin (Gygax, 1971). This argues for rec-
ognition of the gland [named after the French morphologist/anatomist, George Louis
Duvernoy (1777-1855); Taub, 1966] as a separate entity, rather than perpetuating the
term “parotid gland” commonly used for Duvernoy's gland up until the mid-twentieth
century. Some authors have emphasized the common primordium of the venom gland
and associated fangs. This is the case even in species in which the adult fang ends up
at the anterior end of the mouth, with the gland posterior to the eye (Jackson, 2003).
Although Duvernoy's gland has been long-recognized as a structure distinctive to some
colubroids other than those with front fangs (viperids, elapids, and atractaspidids),
Duvernoy's glands have been described in some atractaspidids, based on their mac-
roscopic coarsely lobulated appearance and dorsolateral position, at the corner of the
mouth (Greene, 1997; Haas, 1931; McDowell, 1986). The high-pressure venom glands
of atractaspidids are very different from those of viperids and elapids in lacking a discrete
accessory gland, possessing a distinct histochemical profile (Kochva, 1978), and having
a gland compressor muscle that is derived from the adductor externus medialis (Jackson,
2003), while the compressor glandulae , adductor externus profundus , and pterygoideus
functions as the venom gland compressor in viperids, and the adductor externus super-
ficialis ( levator anguli oris ) in elapids. However, the interpretation of co-existence of
these glands is problematic (Underwood, 2002; Weinstein et al., 2010), and may be a
misinterpretation of a rictal gland. Confirmation and further careful morphological analy-
sis of the buccal glands of various Atractaspis spp. is desirable, as possible concomitant
presence of both glands may serve different or complimentary functions.
2.3 Theories Considering the Evolution of Canaliculated
Fangs and Enlarged Grooved Teeth
Studies of the development, formation, and specialized adaptation of snake teeth have
facilitated improved understanding of the evolution of the “business end” of venom-
delivery systems. Buchtová et al. (2008) found that ophidian tooth formation dif-
fered from that of rodents. The majority of snake teeth were found to bud off a deep,
ribbon-like dental lamina rather than as separate tooth germs. Asymmetries in cell pro-
liferation and extracellular matrix distribution before and after ingrowth of the dental
lamina suggested that localized signaling by a secreted protein was involved (Buchtová
et al., 2008). Using two pythonids [African rock python, Python sebae ( Plate 2.9A ),
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