132 



Cmierian System qf Zoology. 



The general plan of the skeleton is the same in each class, 

 though it admits of considerable modifications, as may be per- 



ceived by the annexed figures. Fig, 30. a represents the hu- 

 man skeleton, man being placed at the head of the mammiferous 

 class ; b, the skeleton of a bird ; c, that of a frog ; and d, the 

 skeleton of a fish. Man is preeminently gifted by his Creator 

 with superior intellectual powers, he is distinguished also by 

 his erect posture, which required a structure varying consi- 

 derably from that of mammiferous quadrupeds: had we 

 chosen the skeleton [of any of the lower orders of this class, 

 the form would have approached more closely to those of the 

 other classes, but taking the extremes of the grand division of 

 vertebrated animals, we still perceive the leading characters 

 of the osteology to be the same. Namely, a skull containing 

 the brain, supported by the vertebral column which contains 

 the spinal cord, and to which the ribs are attached. With 

 respect to the limbs, they admit of a great variety of form 

 suited to the wants of the animal, and in the lowest order 

 of the mammiferous class, which comprises dolphins and 

 whales, we find only one pair of limbs, and in the latter, 

 they are so concealed in the flesh, as not to be visible. The 

 upper limbs of birds do not terminate in toes or claws. Some 

 reptiles have only one pair of limbs, others, as serpents, have 

 none. 



The distinctive characters of the four classes above enume- 

 rated founded not on the form of the skeleton, but on the 

 circulation and respiration, are thus given by Cuvier. 



Mammiferous Animals have a double circulation, and 

 the aerial respiration is simple, viz. it is effected by the lungs 

 only. 



