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CHAPTER IX. 



MAMMALIA. 



§ 1. Mammalia in general. 



The singular animals, so remarkable for their anomalous 

 shapes, their torpid vitality, and their amphibious constitu- 

 tion, which have lately occupied our attention, appear placed 

 by nature as forms of transition, in the passage from those 

 vertebrated animals which dwell in the water, to those 

 which inhabit the land. The class of Mammifera^ or Mam- 

 malia^ comprehends all the animals which possess a spinal 

 column, breathe air by means of lungs, and are also warm- 

 blooded, and viviparous, conditions which render it neces- 

 sary that they should possess organs, called m^ammse, en- 

 dowed with the power of preparing milk for the nourish- 

 ment of their young; a peculiarity from which the lame of 

 the class is derived. But they are not exclusively land 

 animals; for among the mammalia must be ranked several 

 amphibious and aquatic tribes, such as the seal, the walrus, 

 the porpus, the dolphin, the narwal, the cachalot, and the 

 whale; animals which, however widely they may differ in 

 their habits and external conformation from terrestrial quad- 

 rupeds, possess, in common with the latter, all the essential 

 characters of internal structure and of Junctions above enu- 

 merated. These characters belong also to the human spe- 

 cies, which must consequently, in its zoological relations, be 

 ranked as a genus of the class mammalia. So numerous, 

 indeed, are the analogies wjiich connect the natural families 

 of this class with our own race, that we must ever feel a 

 deep interest in the accurate investigation of their compara- 

 tive anatomy and physiology; and it has been found, accord- 

 ingly, that the progress which has, of late years, been made 



