280 REPTILIA. 



THE THIRD ORDER OF REPTILES. 



THE SERPENTS (Ophidia). 



These have no feet, and are consequently, of all others, the Reptiles which most merit the 

 name. Their extremely elongated hody progresses hy means of folds pressed backwards against 

 the ground. They divide into three families. 



THE FIRST FAMILY OF OPHIDIANS,— 



The Orvets — 

 Retains the skull, teeth, and tongue of the preceding group of Seps, and the eye has three lids, &c. 

 whence they are merely Seps without feet. Such are 



The Orvets (Anguis, Lin.), — 

 Externally characterized hy imbricated scales, which cover them all over. We subdivide them into 

 four subgenera, the three first of which have a shoulder-bone and pelvis beneath the skin. 



The Pseudopodes {Pseudopus, Merrem) have the tympanum visible externally, and a small prominence on each 

 side of the anus, which contains an ossicle analogous to a femur, articulated to a true pelvis beneath the skin; 

 the anterior limbs are only represented by an inconspicuous depression, and have no internal humerus. One of 

 the lungs is a fourth shorter than the other. The scales are square, thick, and semi-imbricated, and between 

 those of the upper and lower parts is a groove of smaller scales on each side. 



The Ophisaurs {Op/iisaw-iin, Daud.), merely differ in the absence of external rudiments of limbs, but retain the 

 tympanum, and have one lung a third shorter than the other. 



The Orvets (Anguis, Cuvier), have no trace of limbs externally visible, and their tympanum even is couched 

 beneath the skin ; their maxillary teeth are crooked and compressed, and they have none on the palate. The body 

 is sQrrounded with imbricated scales, without any lateral fold, as in the preceding ; and one of the lungs is shorter 

 by half than the other. [A species, known as the Slow-worm, or Blind-ivorm, is of common occurrence in Britain, 

 and throughout Europe. When alarmed, it constricts its muscles, and is then singularly brittle.] 



These three subgenera have still an imperfect pelvis, a small sternum, scapulars, and also clavicles, hidden 

 beneath the skin ; and the absence of these several bones characterizes 



The Acontias (.4co«<("a, Cuv.), which, in the structure of their head and eye-lids, still resemble the preceding; 

 their anterior ribs are connr':ted all round, beneath the trunk, by cartilaginous prolongations ; and they have one 

 middle-sized lung, and another very short one. Their teeth are small and conical, and I think that I have per- 

 ceived some on the palate. They are easily known by having the muzzle closed by a sort of mask. 



THE SECOND FAMILY OF OPHIDIANS,— 

 The True Serpents, — 



Which is much more numerous, is composed of genera with neither sternum nor vestige of shoulder, 

 but the ribs of which still encircle a great part of the trunk, and the vertebrae are still articulated by 

 a convex facet applied to a concave facet of the succeeding one. They have no third eyelid, nor 

 tympanum ; but the small bone of the ear exists beneath the skin, and its handle passes behind the 

 tympanic bone. Several have also, under the skin, a vestige of hind-limbs, which in some even shows 

 itself externally in the form of a small hook. 



We subdivide them into two tribes. 



That of the Double-Marcheurs [which progress either head or tail foremost,] have still the lower 

 jaw fixed as in all the preceding Reptiles, by a tympanic bone, articulated direct to the cranium, the 

 two rami of this jaw anchylosed at the symphysis, and those of the upper fixed to the skull, and to 

 the intermaxillaries ; so that their swallow cannot dilate as in the following tribe, and their head is of 

 even size with their whole body ; a form which enables them to progress backwards or forwards with 

 the same facility. The bony frame of the orbit is incomplete behind, and the eye is very small. 

 Finally, their body is covered with scales, the anus very near its extremity, the trachea long, and the 

 heart placed far backwards. None of them is known to be venomous. 



There are two genera, one of which approximates to the Chalcides and Bimanes, and the other to 

 the Orvets and Acontias. 



The AMPHISB.ENES {Amphisbcena, Lin.) — 

 Have the whole body surrounded with circular ranges of square scales, as in the Chalcides and Bimanes 



