348 LOWER VERTEBRATES. 



Order I. — OPHIDIA. 



The characteristics which separate the ophidians or serpents from the other 

 orders of the Reptiles may be briefly stated as follows: An elongated body, 

 protected by scales, which cover, proportionally, much less of the integument than 

 those of the higher reptiles, or those of the fishes, and are so attached as to allow con- 

 siderable distention of the underlying skin. Limbs are rarely represented, and never 

 except as a pair of posterior rudiments. The tongue, capable of protrusion, is of a 

 dark red or blue-black color. A urinary bladder is not present. Though themselves 

 small in diameter, the ophidians prey on animals of considerable size, and that these 

 may be swallowed whole, the entire structure of the body is specially adapted. The 

 bones of the skeleton, including those of the head, except those whose special func- 

 tion is to protect the brain, are not anchylosed as in most other animals, but connected 

 by ligaments only, allowing the bones considerable individual movement ; this spe- 

 cialization is characteristic. In general form the serpents may be regularly cylin- 

 drical, there being no external constrictions marking the divisions of the body, as 

 head, trunk, and tail ; or the several portions may be very distinctly shown. The 

 head is, in the majority of common snakes, of a depressed, conical shape, though in 

 some it is flat and triangular, or rounded and fusiform. The mouth is generally large 

 and distensible; though in forms like Typhlops^ it is small, and capable of only limited 

 expansion. The body — or, more properly, the trunk — is ordinarily cylindrical, though 

 many forms have the power of laterally expanding it so as to give them, when viewed 

 from above, the appearance of more than actual size, this habit is possessed by many 

 of the Proteroglyphs, forms like Naja having even the bones of the neck specialized 

 to this end. Lateral compression and vertical expansion is characteristic of many 

 innocuous forms, especially so of the tree-snakes. The tail of ophidians, that portion 

 of the animal behind the vent, presents as much variation in general outline as any por- 

 tion of the body. Though generally round and tapering, in Silybura it is short and 

 truncate ; in many underground snakes it is rounded, stout, and blunt, performing the 

 office of a lever ; and in the sea-snakes (Hydrophidte) it is compressed and vertically 

 expanded. It may be terminated by a small cap-like scale, as in many common forms, 

 by a short spine, as in some of the Opoterodonta ; by a long spine, as in Acantho- 

 phis and Pityophis ; by a rattle, as in the Crotalidae, or it may be simply fusiform and 

 scaled. 



In regard to the organs of special sense, the ophidians are somewhat defective. 

 The sense of sight, from observations made by Dr. Yarrow, seems to be more or 

 less imperfect, and though the eyes, being unprovided with lids, must be incessantly 

 on the alert, they are by no means the chief organs for discovering the whereabouts 

 of the prey, the senses of smell and touch here being of chief value. Younger 

 snakes have the eyes proportionally larger. The sense of hearing is dull, so much so 

 that "as deaf as an adder" has become proverbial. There are no external organs of 

 hearing, and it is probable that reptiles feel the jar produced by an approaching 

 animal rather than that they distinctly hear it. The sense of smell is more acute, and 

 by it the animals find their food, as well as their mates ; many are known to exude a 

 most permeating odor. The nostrils are placed at the apex of the snout, and, in those 

 forms which are aquatic, are provided with valves. The tongue is a tactile organ, 



