THIRD GREAT DIVISION OF THE ANIMAL 

 KINGDOM. 



ANIMALIA ARTICULATA. 



THIS third general form is as well characterised as that of the 

 Vertebrata ; the skeleton is not internal as in the latter, neither is it 

 annihialted as in the Mollusca, tho articulated rings which encircle 

 the body, and frequently the limbs, supply the place of it, and as 

 they are usually hard, they furnish to the powers of motion all 

 requisite points of support ; so that here, as among the Vertebrata, 

 we find the walk, the run, the leap, natation and flight. Those 

 families only are restricted to crawling which are either deprived of 

 feet, or in which the articulations are membranous and soft. This 

 external position of the hard parts, and the internal one of the muscles, 

 reduce each articulation to the form of a sheath, and allow it but two 

 kinds of motion. When connected with the neighbouring parts by a 

 firm joint, as happens in the limbs, it is fixed there by two points, and 

 can only move by ginglymus, that is, in one single plane, a disposition 

 which requires a greater number of joints to produce the same variety 

 of motion. A greater loss of muscular power is also the result, 

 and consequently more general weakness in each animal, in proportion 

 to its size. 



But the parts which compose the body are not always articulated 

 in this way ; most generally they are only united by flexible mem- 

 branes, or they fit into each other, and then their motions are more 

 various, but have not the same force. 



The system of organs in which the Articulata resemble each other 

 the most, is that of the nerves. 



