Fig. 3. Under side of the same. **, lower labials; cc, chin-shields; m, mental or median lower labial.
It will be observed that some of these shields can be seen both in the profile and the others as well; as, for instance, the temporal and the labial or lip shields. The study of them is simplified by the initial letter of each name being used in reference to them. The names used also speak for themselves; as mental, the chin shield; nasals, near the nostril; rostral, the beak shields.
Ophiologists in deciding species, etc., enumerate those which are more than a pair as ‘upper labials’ so many, ‘lower labials’ so many. In some snakes these shields are so large as to cover nearly the entire head; in others, they are almost inconspicuously small, or absent altogether, and much varied, as we shall see.
In the vipers the head is generally covered with small, rigid, imbricated, or overlapping scales instead of plates, and in some the scales are so extremely fine and closely arranged as almost to represent short bristles. This is noticeable in the African ‘nose-horned viper’ (Vipera nasicornis), p. 322, where they present a curiously complicated structure.
| Magnified carinated scale. | — | Magnified head-scale of Vipera nasicornis, of the coloured illustration. |
Too minute to examine except under the magnifying-glass, or to attempt to illustrate, we can convey only a general idea of these curious viper scales, which to the touch are spinous, and rough as a coarse brush. They must form an unpleasant perch for a bird, if it be true that the latter is enticed by the horns of some vipers to come and peck at them, as at a worm. These rigid head-scales become gradually larger and more simple on the body, but are still comparatively small for so large a serpent. In some few of the viperine snakes, plates are present as well as the fine scales, though chiefly about the nose and mouth, exceptions which are now and then found in non-venomous ones also. The preceding three illustrations are the head shields of a Colubrine snake, in which a greater uniformity prevails. Below are given four other types, though even here variations are constantly occurring.
Fig. a. One of the Indian Crotalidæ. It has two conspicuous supraciliary shields, two equally conspicuous anterior frontals over the nostril. The rest are small, and those on the top are absent altogether. The scales are all finely carinated.
Fig. b. The head of a Colubrine snake in which the same scales appear as those in Fig. 1 of the preceding page, viz. two orbitals, etc., but are all much smaller, and do not therefore more than half cover the head.