THE POISONOUS SNAKES OF INDIA. 
47 
northern snake of Europe, our common viper, has its limit 
at 62°. 
Serpents constitute one of the best marked orders of ver- 
tebrate animals. It is true that their external form is paro- 
died by the so-called spurious snakes, or pseudophidians, and 
still more closely by certain lizards. Some of the extinct 
lahyrinthodonts would seem, also, to have had a snake-like 
body. Both these and their recent allies, the pseudophidians, 
are easily distinguished from the serpents by most of the 
characters which separate the class of batrachians from that of 
reptiles properly so called. Moreover, the pseudophidians 
have the tail absent or very short, and the scales, which are 
quite rudimentary, placed between transverse wrinkles of the 
smooth glutinous skin. 
It is more difficult to distinguish snakes from snake-like 
lizards, but the difficulty is not so great as at first appears. 
Those who ought to know better often erroneously state that 
the transition from serpents to lizards is so gradual that no- 
where can a line of demarcation between them be drawn — an 
j error copied in most text-books of zoology. Some have gone 
I so far as to place snakes and lizards in the same order. But, 
I in truth, the supposed passage from one of these groups to the 
, other is effected only by means of such characters as the 
i presence or absence of eye-lids, the form of the body, the 
relative elongation and consequent asymmetry of the lungs, the 
appearance of the scales, and the developement of posterior 
limbs. Not to mention other characters, all serpents are 
sharply differentiated from lizards by the structure of their 
skull and jaws, and by their total want of a shoulder-girdle. 
Nevertheless it is curious to note the cross relationships 
between the two orders. Thus, some of the more typical snakes 
have traces of hind limbs, while we find lizards witli well de- 
veloped limbs, and not their aberrant congeners, exhibiting 
a near approach to that peculiar and complex articulation of 
the vertebrae found in most serpents. 
With three striking exceptions,* no other order of vertebrate 
animals is more extensive than that of serpents. The number 
of known species may be estimated at a thousand, of which 
two hundred are venomous. These venomous snakes we shal 1 
now exclusively consider, with special reference to those which 
inhabit the peninsula of India. 
* These are (1) carinate birds, (2) acanthopterous fishes, and (3) phys- 
tomous fishes. Lizards and the mammalian group of rodents are, next t 
serpents, richer in species than any other orders of vertebrates, so far as a 
present known. 
