SUBKINGDOM 



VERTEBRATA. 



The five great Classes usually regarded as forming this province 

 of the Animal Kingdom have a common type of structure, clearly 

 recognizable in most members of the series. The most evident 

 characteristic is an internal jointed skeleton, made up of vertebra^, 

 which with their processes form two cavities — ^the upper (neural), 

 enclosing the great nervous cord, the lower (haemal or enteric), con- 

 taining the viscera. 



The history of Mammals, Birds, Reptiles, Amphibians and Fishes, 

 as a sub-kingdom, reaches back to the Upper Silurian Age. Their 

 fossil bones and teeth, have been found in every stage of alteration, 

 from their natural state to that of complete petrifaction, and demon- 

 strate the existence of numerous tribes of highly organized beings 

 in the early ages of the world, and the continuance of the same 

 general type of organization to the present day. The earliest ver- 

 tebrate animals were the cold-blooded, water-breathing class in the 

 Upper Silurian. The type, however, began with the generalized 

 forms — the Ganoids and Sharks ; the common bony fishes, now 

 swarming in river, lake and ocean, not coming into existence until 

 the Jurassic Period. Amphibians and Reptiles were introduced in 

 the Carboniferous. In the Reptilian Age came the first Birds and 

 the first Mammals, but the typical Birds and Mammals had their 

 full expansion in the Tertiary. 



