224 PYTHON. COLUBER. 



directed outwards, (PL 65 b. fig, 2). These sinuous terminations of 

 the calcigerous tubes give a very peculiar appearance to the dentine 

 of the Python, which, viewed by transmitted Hght in thin sections 

 by a low power, seems, at first sight, to be invested by a 

 thick layer of some distinct tissue, (fig. 1, b). Another charac- 

 ter, which was detected by Retzius(l), is displayed by a longitudinal 

 section of the dentine of the Python, when viewed by transmitted 

 light with an objective of ^th inch focus. It is the transmission from 

 the lower or concave side of the main calcigerous tubes of numerous, 

 minute, parallel and nearly straight branches, directed obliquely out- 

 wards and downwards. These minute branches are not only given 

 off from the main calcigerous tube, but also from its primary branches, 

 which differ from the dichotomous divisions of the calcigerous tubes 

 in other teeth, in being much smaller than the main tube ; they also 

 run parallel with each other and are given off at an acute angle from 

 the under side of the calcigerous tubes. The structure of the external 

 layer of cement (c c, fig. 1, PI. 65 b.) can only be examined in 

 sections taken from near the base of the tooth, as its extreme thinness 

 in the crown causes it to appear merely as a clear line bounding the 

 peripheral loops of the calcigerous tubes. It appears to be more readily 

 detached from the dentine where it is thickest at the base of the tooth 

 than in other teeth : portions of it adhering to the section figured are 

 shown at c c, fig. 1, PI. 65, b. It is a clear substance in which 

 the calcigerous cells are simple, very minute and inconspicuous. 



95. Coluber. — The solid teeth of the smaller non-venomous serpents 

 correspond in structure with those of the Python and Boa. In the 

 Erix turcicus the largest and longest teeth are placed at the anterior 

 part of the series, and they diminish as they recede backwards : this 

 is the usual disposition. But in the common harmless snake {Natrix 

 torquatus) the proportions of the maxillary teeth are reversed and the 

 largest are at the posterior part of the series. In the Coluber filiformis, 

 the teeth are equal and of small size. 



The disproportionate length of the last maxillary tooth is charac- 

 teristic of the colubrine genera Dryinus, Dendrophis and Heterodon ; 

 but the Dryinus nasutus has one tooth in the middle of the maxillary 



(1) Loc. cit. p. 523, PI. xxii, fig. 5. 



