VERTEBKATED ANIMALS. 19 



FIRST DIVISION. 

 VERTEBRATED ANIMALS. 



THE body of vertebrated animals is sustained by a skeleton 

 composed of many pieces connected together, and moveable up- 

 on one another. The body is composed of a head, a trunk, and 

 limbs. The head is formed of the cranium, which includes 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 vertebrae, which move upon one 

 another, all of which have a cylindrical opening in the centre, 

 forming together a canal containing the portion of nervous mat- 

 ter called the spinal marrow. The ribs are semicircular, and 

 protect the sides of the cavity of the trunk. They are general- 

 ly 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 ; sometimes indeed one or other of these pairs is deficient, 

 and sometimes both. According to the motions to which these 

 limbs are destined to be subservient, 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 always red, and seems 

 by its composition adapted to sustain energy of sensation and 

 muscular vigour. 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 vertebrae, and terminate in two medul- 

 lary cavities in the cranium, the volume of which is generally 

 proportioned to the extent of 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. In the greater number the upper jaw is 

 completely fixed and motionless. Both are generally provided 

 with teeth, excrescences of a peculiar nature, similar in chemical 



