CHAPTER VIII. 
Branch VIII. — Vertebrata {Bach-honed Animals). 
General Characters of Vertebrates. — We have seen 
that most of the foregoing types of animals have the body 
protected by a crust or shell, enclosing the muscles and 
other internal organs; but now we come to animals which 
have an internal bony support or skeleton. The skeleton 
consists of a backbone (Fig. 174) with bones forming a 
skull and a series of bones supporting the limbs. Fishes, 
reptiles, birds, and mammals or beasts, are familiar exam- 
ples of vertebrates^ while man himself is a vertebrate. Ver- 
tebrates in general have bodies which are symmetrical, i.e,, 
the two sides repeal each other; they nave a Drain-box or 
skull containing the brain and tne mouth and pharynx, , 
with two eyes, two ears, and usually two nasal openings. 
To the trunk are attached two pairs of limbs; the tore- 
arms in man corresponding to the fore legs of the horse or 
dog. 
Now if we cut a fish in twOa and closely examine the sec- 
tion, we shall notice that above the backbone is a little cav- 
ity containing the nervous cord, and below a much larger 
cavity containing the viscera, i.e., heart, liver, stomach or 
intestine. Thus there are two cavities, the nervous one 
above, and the visceral one be)ow the backbone (Figs. 175, 
176). In this respect the bav^kboned animals differ from 
the backboneless or invertebrate animals, in which there is 
but one body-cavity, with the nervous system situated on 
the floor of this cavity. 
Vertebrates have a true heart, with one, generally two, 
auricles, and one or two ventricles, and, besides arteries and 
