xiii ■ RHACHIODONTINAE DirsADOMORPHINAE 623 



mass. Miss Durham has illustrated this curious process in 

 series of drawings.-' 



Series B. OPISTHOGLYPHA. 



One, or a few, of the posterior maxillary teeth have a groove 

 or furrow in front, which conducts the secretion of the enlarged 

 upper labial glands. Apparently all these snakes are more or 

 less poisonous, paralysing their prey before or during the act of 

 deglutition. So far as man is concerned they are rather harm- 

 less, since the poison is not very strong, not available in large 

 quantities, and above all because the small poison-teeth stand 

 so far back that the snakes cannot easily inflict wounds with 

 them. 



The Opisthoglypha are of considerable morphological interest, 

 since they connect the Colubridae with the Viperidae, the char- 

 acteristic poisonous apparatus of which seems to have been derived 

 from that of the Opisthoglypha by the reduction or shortening 

 of the anterior portion of the maxillaries and the harmless teeth, 

 so that the posterior or poison-fangs come to the front. 



The Opisthoglypha comprise about three hundred species and 

 are cosmopolitan, including Madagascar but excepting New Zea- 

 land. They contain truly terrestrial, arboreal, and thoroughly 

 aquatic forms. 



Sub-Fam. 1. DipsadomorpMnae. — The nostrils are lateral 

 and the dentition is well developed. Long-tailed, terrestrial, and 

 arboreal forms. Most of the arboreal species are green above, 

 often with white or yellow longitudinal bands, while the imder 

 parts are white or yellow. They feed chiefly upon lizards, birds 

 and their eggs. 



Dipsadomoriohus s. Dipsas (part). — Typical, very long-bodied 

 and long-tailed Tree-Snakes, with a vertical pupil. The median 

 or vertebral row of smooth scales is enlarged ; the broad ventral 

 scales are bent at an obtuse angle on the sides, the resulting 

 ridge assisting in climbing. The sub-caudals are arranged in 

 two rows. Ten to fourteen maxillary teeth are followed by two 

 or three enlarged, grooved fangs. 



B. trigonatus, of India, grows to one yard in length. 

 Yellowish olive or pale grey above, with a white, black-edged 

 1 P.Z.S. 1896, p. 715. 



