68 METAMORPHOSES OF THE FROG'S SKELETON. 



In all the fish-like batrachia, called, from a retention of 

 more or less of the branchial apparatus, "perenni- 

 branchia," the limbs are short, and the rays of the 

 terminal segments of each limb are, more or less, united 

 by a web ; the body is long, and the tail long and com- 

 pressed. But a great ascent in the scale of life is made 

 in the batrachian order: all the species when hatched 

 have the fish-like form, and gills for breathing water; 

 most of them exist for some time, under this form, in 

 water ; and these undergo so strange a modification of 

 form and structure before arriving at maturit}^, that it has 

 been called a "metamorphosis." They change their 

 aquatic for a terrestrial life ; they breathe air instead of 

 water ; and from being omniverous become carnivorous. 

 The tadpoles of our common toad and frog afford ready 

 and abundant instances for tracing these stages. The 

 following is an outline of the main phenomena of the 

 change observable in regard to the osseous system : — 



In the development of the skeleton of the common 

 frog, a fibrous and cartilaginous framework is originally 

 laid down conformably with the aquatic habits and life 

 of the larva. A large cartilaginous cranium with four 

 haemal arches, and one of these supporting the framework 

 of the branchial apparatus — a short series of fibro-carti- 

 laginous vertebrse, minus the haemal arches, in the trunk, 

 and a series of fibrous septa diverging from the fibrous 

 capsule of the notocjiord, and defining and giving attach- 

 ment to the muscular segments along the tail — constitute 

 the skeleton of the newly-hatched tadpole. As it grows, 

 ossification begins ; but only in those parts of the skele- 

 ton which are to be retained in the future frog. Thus, 

 the centrums and neurapophyses of the head and trunk 

 are ossified, but not those of the tail. In the trunk, ossi- 



