ICHTHYOPSIDA. 253 
(fig. 136) is short; the dorsal vertebrze are very long ; and the 
ribs are quite rudimentary, their place being taken by greatly- 
developed transverse processes (@). The bodies of the vertebrz 
are hollow in front and convex behind (Jvoce@/ous). The bones 
of the fore-arm (radius and w/nza), and those of the shank 
(t2zjzca and fibula), are united together to form single bones. 
The upper jaw is usually furnished with teeth, and the lower 
jaw sometimes, but there are no teeth inthe Toads. The lungs 
are well developed, comparatively speaking ; and as there are no 
ribs by which the cavity of the chest can be expanded, the air 
is taken into the lungs by a process nearly akin to that of 
swallowing, There can be no doubt, also, that the skin plays 
a very important part in the aeration of the blood, and that the 
frogs, especially, can carry on their respiration by means of the 
skin without the assistance of*the lungs for a very lengthened 
period. This, however, should not lead to any credence being 
given to the often-repeated stories of frogs and toads being 
found in closed cavities in solid rock, no authenticated instance 
of such an occurrence being known to science. The ova of 
the frogs and toads are deposited, in masses or strings, in 
Fig. 137-—Development of the common Frog. a@ Tadpole, viewed from above, 
showing the external branchiz (¢) + 4 Side view of a somewhat older specimen, 
showing the fish-like tail ; ¢ Older specimen, in which the hind-legs have made 
their appearance ; @ Specimen in which all the limbs are preseuit, but the tail 
’ has not been wholly absorbed. (After Bell.) 
water, and the young or larvee are familiar to every one as tad- 
poles. Upon its escape from the egg, the young frog (fig. 137) 
