VERTEBRATED ANIMALS. 25 



cavity, without an outlet. The lowest in the series, which are also the 

 last of the animal tribes, exhibit nothing but a homogeneous pulp, possessed 

 of motion and sensibility. In the preceding divisions, the organs of move- 

 ment and sense are disposed symmetrically, on both sides of an axis ; but 

 in this, they have a circular arrangement, around a common centre. This 

 form of existence Cuvier arranges under the head of Pi.adiated Animals, 

 [Animalia Radiata.) 



The term Zoology, includes the whole of the Animal kingdom ; besides 

 which, different departments have received particular names ; such as Orni- 

 thology, for the birds ; Ichthyology, for the fishes ; Entomology, for insects ; 

 and Conchology, for the testaceous Mollusca. 



FIRST DIVISION. . 



VERTEBRATED ANIMALS. 



The body of vertebrated animals is sustained by a skeleton, composed 

 of many pieces, connected together and moveable upon one another. The 

 body is composed of a head, a trunk, and limbs. The head is formed of the 

 cranium, Avhich incloses the brain, and of the face, composed of two jaws. 

 In the face are the organs of sense. The trunk is sustained by the spine 

 and ribs. The spine is composed of vertebrse which move upon one another, 

 all of which have a cylindrical opening in the centre, forming together, a ca- 

 nal, containing the portion of nerA^ous matter called the spinal marrow. The 

 ribs are semicircular, and protect the sides of the cavity of the trunk. They 

 are generally articulated, by one extremity, to the vertebral column, and by 

 the other, to the sternum. In some species, they are scarcely perceptible. 



The vertebrated animals have never more than two pair of limbs ; some- 

 times, indeed, one or other of these paks is deficient, and sometimes both. 

 According to the motions to which these limbs are destined to be subser- 

 vient, the anterior ones assume the form of hands, feet, wings, or fins ; the 

 posterior, of feet or fins. 



The blood of the vertebrated animals is ahvays red, and seems, by its 

 composition, adapted to sustain energy of sensation and muscular vigor. 

 The correspondence of the blood with the respiration, necessary to the 

 several species of these animals, has suggested their division into classes. *' 



The external organs of sense, in all vertebrated animals, are two eyes, 

 two ears, two nostrils, the teguments of the tongue, and the teguments of 

 the whole body. The nerves unite with the nervous matter in the vertebra?, 

 and terminate in two medullary masses, in the cranium, the volume of 

 which is generally proportioned to the extent of the intellectual capacity. 



There are always two jaws, an upper and under one. The principal 

 motion exists in the lower, which has the power of elevation or depression. 

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