1895.] teeth op certain poisonous snakes. 821 



Pbotebogltpha. 



HtDROPHIINjE. 



The poison-gland in Marine Snakes is situated some distance 

 posterior to the eye. It varies somewhat in external form, and 

 consists of a large series of longitudinally disposed tubules which 

 converge anteriorly towards a central duct ; this passes from the 

 anterior end of the gland as the poison-duct. These tubules are 

 larger towards the central axis of the gland and become smaller 

 and much branched towards the periphery. They have spacious 

 cavities, and their lining epithelium consists of short regular 

 columnar cells. The cell-contents are for the most part aggregated 

 at the base of the cell, at which point the nucleus is situated ; the 

 rest of the cell presents a finely granular appearance. 



The poison-duct is of rather large calibre, and small tubules open 

 into it along its whole course from the gland to the teeth, though 

 they become much fewer in number anteriorly. As the duct 

 nears the poison-fangs it becomes sinuous, bends suddenly inwards 

 at the anterior extremity of the maxilla, and on reaching a point 

 just anterior to the bases of the two grooved teeth it enlarges, 

 enclosing a more or less considerable transverse vertical cavity. 

 Into this cavity project two large cushions of muscular tissue, one 

 in front of each tooth (PI. XLVI. fig. 13 and 14, m). The two 

 cushions are precisely similar and quite distinct from each other, 

 the vertical slit between them being the only communication 

 between this cavity, enclosed by the enlarged termination of the 

 poison-duct, and that enclosed by the folds which closely surround 

 the teeth (PL XLVI. fig. 14). The muscular tracts extend a short 

 distance parallel to the teeth down the inner edge of the fold. 

 The fibres are arranged in such a manner that contraction would 

 lessen the cavity at the termination of the duct, widen the passage 

 between the two muscular cushions, and also bring the folds into 

 closer approximation with the outer faces of the teeth. This 

 ensures a free passage for the poisonous secretion from the duct 

 to the bases of the grooved teeth. There is also a fold partition'ng 

 off the two grooved teeth from each other, and the secretion passes 

 down one side to one tooth and down the other side to the other 

 (c/. PL XLVI. fig. 14). 



As in the Opisthoglyphous Snakes, the reserve teeth are never 

 in communication with the poison-duct until they become 

 functional owing to loss of teeth previously in use. 



The labial glands are very similar to those previously described 

 and have a series of ducts, which become very numerous at the 

 anterior extremity of the jaw. 



Genus Enhydbis. 



Species examined : — E. hardivicTcii. 



The superior labial gland is of very small bulk posteriorly and 

 much elongated, being but a thin line of glandular tissue under 



