85 
that of tortoises, that only the cervical and caudal 
vertebre have true articulations admitting of mo- 
tion. The dorsal and sacral vertebrae, even when 
they are not consolidated, are connected by strong 
ligaments, so as to form an inflexible column.” 
As in the frog the first tarsal bones, viz. the as- 
tragalus and os calcis, which are much elongated, 
and, placed in the same relative position to each 
other as the tibia and fibula in the human subject, 
form a separate phalanx below the bones of the leg; 
so in birds we find a single long bone (commonly 
called the leg) which supplies the place, not only of 
some of the tarsal bones, but also of the metatarsal. 
From the lower end of this bone project usually 
three, but in the two-toed ostrich only two processes 
or rudiments of metatarsal bones, supporting the 
toes. In the penguin the true character of this bone 
is evident, as its body divides in the middle into 
three distinct bones. The penguins, auks, and puf- 
fins, being nearly plantigrade, vary from all other 
birds, approaching to the type of the mammalia in 
this respect. 
** In frogs the bones of the trunk are very simple. 
The ribs are wanting; in which respect, as well as 
in many others, we may observe an approximation 
to the type of cartilaginous fishes, e. g. of rays. It 
is occasionally only, as in the rana pipa and the 
salamanders, that small appendages, rather cartilagi- 
nous than bony, forming rudiments of ribs, are at- 
tached to the transverse processes of some of the 
vertebre. In these animals there is consequently no 
G 3 
