TYPICAL FROGS. 
265 
leg. Moreover, the hind-limb obtains a kind of additional segment, owing to the 
elongation of the calcaneum and astragalus in the ankle-joint, which form a pair 
of long bones lying parallel to one another. As a rule, frogs and toads undergo a 
lengthened larval period; the “ tadpoles,” as shown in the figure on p. 262, having 
a globular head and body, a fish-like tail, external or internal gills, and no limbs in 
the first stages of their existence. The hind-limbs are the first to appear, and 
after the front pair are developed the tail is gradually absorbed, upon which the 
young for the first time leave the water. Represented by about a thousand species, 
frogs and toads have a worldwide distribution, although more abundant in tropical 
and subtropical than in temperate regions, and being especially numerous in India 
and South America; and it is not a little remarkable that some of the largest 
forms are inhabitants of islands. From the nocturnal habits of the adults it is 
frequently difficult to find out whether in any locality these reptiles are abundant 
or the reverse ; but in the spring this may generally be ascertained by observing 
the tadpoles in the rivers and points, since all of these show specific differences, to 
the full as well marked as those in the adult. 
The Typical Feogs. 
Family Rapidje. 
The typical frogs, together with four other families, constitute a suborder 
(Firmisternia), characterised by the presence of a tongue, and by the firm union 
of the two metacoracoid bones of the chest by means of a single cartilage uniting 
their free edges. From the other members of the group, the typical frogs are 
distinguished as a family by the presence of teeth in the upper jaw, and by the 
transverse processes of the sacral vertebra being either cylindrical, or but very 
slightly dilated at their extremities. These characters are sufficient to distinguish 
the typical frogs from the other families of the suborder; but it may he added that 
the vertebrae are cupped in front and hollowed behind; while there are no ribs 
and the terminal style of the backbone is articulated to the sacrum by two 
condyles. The terminal joints of the toes may be either simple or pointed, 
T-shaped, Y-shaped, or even claw-like ; the species in which these joints, are thus, 
expanded having the soft parts similarly expanded and flattened. For a long time 
it was considered that the shape of the tips of the toes was connected with the 
mode of life of their owners; and although this is so to a great extent, it is now 
ascertained that several of the species in which the toes are somewhat expanded 
are as aquatic as those in which they are pointed, and species presenting both 
modifications are included within one and the same genus. The typical frogs are- 
divided into twenty genera, only two of which are noticed in this work. 
Under the general title of water-frogs may be conveniently 
Water-Frogs. - n( q u q e q a p the members (some hundred and forty in number), of the 
genus Rana, to which belongs the common English frog. The distinctive characters 
of these frogs are to be found in the horizontal pupil of the eye; the more or 
less deeply notched and free tongue; the presence of teeth on the vomerine bones 
of the palate; the absence of webs in the toes of the fore-feet, and their presence 
