■ INTODUCTION. 61 



of them, with whatever names they may have been 

 decorated, are but slight modifications of the pri- 

 mary : and consist entirely in the addition or de- 

 velopment of certain parts which make no essen- 

 tial change in the general character of their con- 

 formation. 



In the first of these general forms or models, in- 

 cluding that proper to man, and the animals resem- 

 bling him most nearly, the brain and the chief 

 trunk of the nervous system are inclosed in bony 

 coverings, the former called the cranium, and the 

 latter the vertebra. To the sides of the vertebra, 

 as to a central column, are attached the ribs and the 

 bones of those limbs, which form as it were the 

 framework or carpentry of the body. The muscles 

 generally speaking, form a second covering for the 

 bones which they put into action, and the viscera 

 are inclosed in the head and trunk. 



Creatures of this form are denominated " verte- 

 brated animals" (animalia vertebrata.) 



These have all red blood, a muscular heart, a mouth 

 with two horizontal jaws, distinct organs of vision, 

 smell,. hearing, and of taste, situated in cavities of 

 the head, and never more than four limbs. The sexes 

 in these animals are invariably separated, and a si- 

 milar distribution prevails among them of the me- 

 dullary masses, and of the principal branches of the 

 nervous system. 



On a close examination of each of the parts of this 

 grand system we shall discover a general analogy 



