326 Animal Life 
termed) are classed in a single family, the Botde. This family is divided into two 
eroups or sub-families, the first of which includes the true pythons of India and the 
Malay countries, as well as the African rock-snakes and the Australian and Papuan 
carpet-snake. Unfortunately it likewise includes a single aberrant species from Southern 
Mexico, so that in the zoological sense there is some justification for saying that 
pythons occur in the New World. 
Worse confusion occurs in the case of the second sub-family—the Boine of the 
naturalist—since, in addition to the typical boas of Tropical America, and their outlying 
representatives in Madagascar, the group includes the snakes of the genus Hryz, which 
are natives of North Africa, Greece, and South-Western Asia, as well as certain Papuan 
and Pacific Island forms, all of which are, in one sense, entitled to be called boas. 
In the present article the latter term will be restricted to the larger snakes of 
Tropical America and their immediate, although smaller, relatives, while by pythons 
will be meant only the snakes properly so called, together with the African rock-snakes, 
the Australian carpet-snake, etc. 
In, common with other snakes, boas and pythons are enabled to twine their 
bodies into the well-known unbroken and regular coils owing to the structure of the 
vertebree and the loose articulation between these and the exceedingly numerous ribs. 
Fig. 1. Front, hind, and lateral aspects of a vertebra of a Python; ms, dorsal spine; mp, lateral process; 
nm, neural canal; ze and ze’, pre- and post-zygapophyses; 2t, zygantrum and zygosphene; ¢ and c’, anterior 
cup and posterior ball; ha and hp, ventral spine; a and d, articular surface for rib. 
Snake-vertebree, as shown in Fig. 1, are characterised by possessing more interlocking 
surfaces than are to be found in those of most other animals, whereby the coils are 
formed with greater regularity and smoothness than would otherwise be the case, 
while the risk of dislocation is proportionately lessened. In addition to the ordinary 
articular facets known as pre- and post-zygapophyses, common to vertebrates in general, 
each vertebra of a snake has a wedge-shaped articular process known as the zygosphene 
which fits into a corresponding cavity—the zygantrum—in the adjacent surface of the 
next vertebra, whereby a most firm, and at the same time mobile, joint is secured. 
It is somewhat remarkable that a similar mode of articulation of the vertebre is met 
with in the iguana lizards of America. As other lizards get on perfectly well without 
such additional facets, it is difficult to understand why they should be developed in 
the iguanas, unless indeed it is a foreshadowing of the serpent type. Not that I 
mean to imply that iguanas are the ancestors of snakes; but it may well be that 
those lizards from which serpents took origin had vertebree of this complicated type. 
If this suggestion prove true, it would be very difficult for those who believe that 
unaided survival of the fittest has been the prime cause in animal evolution to 
explain why these ancestral lizards should have acquired a type of vertebre apparently 
necessary only to serpents. 
