THE POISONOUS SNAKES OF THE ANGLO-EGYPTIAN SUDAN 
175 
smootli). All true vipers possess a very short upper jaw (Plate XIX., c), which is not firmly 
united with the adjacent hones of the head, hut movable in a vertical jilane and provided 
with two long fang-like teeth curved somewhat backwards ; further teeth (reserve teeth) 
just behind them may also he present and take their place when they have fallen out. 
The fangs lie on the palate, with the sharp points directed backwards ; they 
are covered nearly to the tips with a sheath, which is retracted when the snake opens its 
mouth to bite. In this case the mouth is widely opened, the upper jaws turn forward and 
their fangs become erected, the tips pointing even somewhat forward ; all this takes place 
at the very moment when the snake throws its head forward against its prey or offender, 
and the fangs can then enter the llesh of the victim with considerable force. They are, if 
possible, withdrawn immediately afterwards. If the victim should make a violent move¬ 
ment in a contrary direction, a fang may be lost and remain in the llesh ; in this case, 
the reserve fang may take its place, when it is the normal time for the fang to be changed. 
Apart from their attachment to a movable, short upjjer jaw, the fangs are themselves 
different from those of the Najas, by their not being grooved at the front margin, but 
entirely channelled longitudinally by a poison-canal, an opening existing only at the base 
and just above the point of the tooth. 
The poison-gland is in both the poisonous colubrine snakes and tbe true vipers a Poison-glands 
modified part of the salivary gland of the upper jaw (supramaxillary gland), and is 
connected by a narrow duct to the base of the poison-fang. The poison runs down to 
the tip of the fang along the groove in the Najas, and in the poison-canal in the true 
vipers. 
The constriction of the poison-gland, whereby the poison is expressed, is caused by 
the pressure of a ligamentous jugal band on the gland ; this band is supported more or ^ 
less in its action by the muscles of the upper jaw. In the genus OaMsHs the poison- 
gland is very large and prolonged backwards beyond the insertion of the lower jaw 
(Plate XIX., c); here the muscles alone are effective in pressing out the poison. Further 
information on the poisonous apparatus of the snakes is to be found in the following 
excellent publication ;— 
Stejneger, L. : “The Poisonous Snakes of North America.” In Eepart of the United 
States National Museum. Washington, 1893. 
The following descriptions are chiefly taken from G. A. Boulenger’s standard work. 
Catalogue of Sna-kes in the liritish Museum, but are a little modified in some cases, 
as Sudanese specimens differ (especially in colour) from the descriptions in this book. 
I have given only the most essential indications as regards the literature and references 
to good figures, but hope that this paper will be useful for the recognition of the poisonous 
snakes of the Sudan. 
Descriptions of the Sudanese Venomous Snakes' 
I. ProterogUjphous Colubrine Snakes 
Anterior teeth of the upper jaw enlarged, with a longitudinal groove along the front 
surface, conveying the poison from the duct of the poison-gland to just above the point of 
the tooth. Ujiper jaw more or less elongate, not erectile. Loreal plate of the head-shields 
constantly missing in both Sudanese species. 
Genus : Naja, Laurenti 
A pair of large grooved poison-fangs, followed after an interspace by one to three small, 
faintly-grooved teeth, situated near the posterior end of the upper jaw (Plate XVII., fig. 1, r). 
Fur exjjlamitiou of scientific terms, sec Appendix, /> a^’c 185. 
