282 REPTILIA. 



The Boas more particularly so named, have a hook on each side of the anus ; a compressed body, 

 larger towards the middle ; a preliensile tail ; and small scales, at least on the hinder part of the head. 

 Among them are found the largest of all Serpents, certain species attaining a length of thirty or forty 

 feet, and being capable of swallov.ing Dogs, Stags, and even Cattle, at least according to some narra- 

 tors, after having crushed them within their folds, lubricated them with their saliva, and enormously 

 dilated their jaws and gullet. This operation lasts a long while. A remarkable particular of their 

 anatomy consists in their having one lung but half shorter than the other. [At the extremity of the 

 great lung in all this tribe is an extremely capacious air-bag, the use of which appears to be for con- 

 taining the air requisite for respiration, when the nostrils are closed by the tedious process of degluti- 

 tion.] We subdivide these Serpents according to the teguments of the head and jaws. 



Some have the head covered as far as the tip of the muzzle with small scales resembling those of the body, and 

 the plates which invest the jaws are not furrowed with grooves. Others have scaly plates beneath the eyes as far 

 as the muzzle, and no furrows to the jaws. Some, again, have scaly plates upon the muzzle, and grooves upon 

 those of the sides of the jaws. There are some with plates on the muzzle, and the sides of the jaw hollowed into a 

 slit-like chink beneath the eye and further backward. And, lastly, some have no furrows, and the muzzle 

 invested w ith plates but slightly prominent, which are obliquely cut backwards in front and truncated at the tip, 

 so as to terminate in corners : these have the body much compressed, and the back keeled. They inhabit the 

 East Indies whereas the others are from America, and should form a distinct subgenus — Cenchris, Gray. 



The Scytals {Pseudohoa, Schneider). 



Plates, not only on the muzzle, l)ut over the cranium, as in tlie Snakes proper ; no grooves, the body 



round, and head even with the trunk, as in the Roles. 



Daudin has likewise separated 



The Eryx,— 



Which differ by having a very short obtuse tail, and by their ventral plates being narrower. The head 



is short and nearly even with the body, characters in which they approximate the Roles, were it not 



that the conformation of their jaws permitted these to distend. The head is covered with small 



scales ; and they have also no hooks near the anus. 



The Erpetons, Lacepede, — 



Are very remarkable for having two soft prominences covered with scales, at the tip of the muzzle ; 



head plated ; the plates of the belly not very wide, and those of the under-part of the tail different 



from the other scales. Their tail, however, is long and pointed. 



The Snakes Proper {Coluber, Lin.) — 

 Comprehended all the species, venomous or non-venomous, the plates underneath the tail of which are 

 divided each into two, or, in other words, ranged in pairs. 



Independently of the subtraction of the venomous kinds, their number is so vast that we are obliged to have 

 recourse to all sorts of characters in order to distinguish them. First, are separated 



The Pythons, Daudin, — 

 Which have hooks near the anus, and narrow ventral plates, as in the Boas, from which they only 

 differ by having the plates underneath the tail double. Their head is plated at the tip of the muzzle, 

 and their lips grooved. Species occur as large as any Boa. 



Some of these Pythons have the first, and others the terminal plates of their tail, simple ; but these are perhaps 

 accidental varieties. 



The Cerlieri, like the true Pythons, have the head entirely covered with small scales, with the exception of 

 plates between and before the eyes ; but they have no hooks near the anus. They have sometimes also simple 

 plates at the base of the tail. 



Xenopeltis, Reinwardt; have great imbricated triangular plates before the eyes, which might be confounded 

 with the scales adjacent to them, only that the latter are smaller. 



Heierodon, Beauvois.— The ordinary plates of this group, but the tip of the muzzle composed of a short single 

 piece, in form a trihedral pyramid, which is a little raised and erected above, a conformation which has induced 

 the appellation of pig-snouted Serpents. 



The Hurria, Daud. — Indian species, with subcaudal i)lates always simple, except those at the point, which are 

 double ; these trivial anomalies, however, merit but little notice. 



The Dipsas of Laurcnti {Biaiffariis, Oppel.)— Body compressed, and very much larger than the head : the range 

 of scales along the spine of the back larger than the others. 



Dendrophis, Fitzinger ; AlKviidla, Gray. — Resemble the last by having a range of broader scales along the back, 

 and narrower scales along the flanks ; but their head is not wider than the body, which is slender and very much 

 lengthened. Muzzle obtuse. 



