(Subfamilies: Viperinæ, Crotalinæ.)
The technical terms employed in the above synopsis will be found explained and illustrated by figures in the chapter on the Skeleton.
No serial arrangement can express the affinities of the various groups as conceived by the classificator; a diagram therefore follows to show the author’s views as to their interrelationships, and possibly their phylogeny. Leaving aside the Typhlopidæ and Glauconiidæ, which should be regarded as burrowing types independently derived from some Ophidian form less specialized than any with which we are at present acquainted, and probably without direct relationship to the Lizards, the family Boidæ, and more especially the Pythons, claim the position of ancestral group, from which all other snakes may have been derived.
| Viperidæ | Amblycephalidæ | |||||||
| Colubridæ opisthoglyphæ | Colubridæ proteroglyphæ | |||||||
| Uropeltidæ | ||||||||
| Ilysiidæ | Xenopeltidæ | Colubridæ aglyphæ | ||||||
| Boidæ | ||||||||
Further remarks on this subject in the chapter on Dentition.
It is to be regretted that paleontology cannot help us at present as concerns the lines of evolution, the comparatively few fossil Ophidians known, from the Lower Eocene upwards, the remains of which can be identified with some measure of certainty, being either non-poisonous types (Boidæ, Ilysiidæ, Palæophiidæ, Colubridæ) or Viperidæ (Viperines from the Miocene of France and Germany, Crotalines from the Miocene of North America). The vertebræ from the Puerco Eocene of America, on the limit between the Cretaceous and Eocene periods, described as the oldest snake remains, Helagras, Cope, are stated to approach the Lacertilian type.
Whether the vertebræ named Symoliophis, Sauvage, from the chalk of France, and Coniophis, Marsh, from the Laramie Cretaceous of North America, are Ophidian, as claimed by their describers, or Dolichosaurian, cannot be decided without further material.
CHAPTER II
EXTERNAL CHARACTERS—INTEGUMENT
The form varies enormously, worm-like in some, comparatively short and heavy, elongate and more or less slender, or extremely gracile and almost filiform, in others. In this respect our common Grass-snake occupies a central position, and for this reason is termed a moderately slender form, anything above or below this standard being described as comparatively short or elongate. Our shortest and stoutest European Snakes are the Vipers, especially Vipera ursinii; our longest and slenderest, the Coluber and Zamenis, especially Zamenis dahlii. These extremes in both directions are, however, far surpassed by many exotic snakes, as we find on comparing, for instance, one of the African Puff-adders (Bitis), with certain Oxybelis and Leptognathus from Tropical America. The body may be somewhat rigid, as in some burrowing and ground snakes, not unlike in appearance to our Slow-worm and other limbless Lizards; or extremely flexible, as in many Pythons and Boas and in the Tree-snakes generally. This flexibility may be accompanied by a vertical compression of the body in relation with an arboreal existence, whilst sluggish snakes, such as most of the Viperidæ, may be remarkable for the flattening of the body, which they may further increase when basking in the sun or in order to assume a more formidable appearance on the approach of an enemy. This power of flattening out the whole or the anterior part of the body is possessed by many snakes, poisonous as well as harmless, and reaches its highest degree in the Cobras of India and Africa, the expanded anterior part being known as the “hood,” from the Portuguese name “Cobra di capello.”