CHAPTER VIII. 

 Branch VIII. — Vektebrata [Back-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 supjoorting the limbs. Fishes, 

 reptiles, birds, and mammals or beasts, are familiar exam- 

 pies of vertebrates^ while man himself is a vertebrate. Ver- 

 tebrates in general have bodies which are symmetrical, i.e., 

 the two sides repeat each other; they nave a Drain-box or 

 skull containing tlie brain and tiie mouth and pharynx, 

 with two eyes, two ears, and usually two nasal openings. 

 To the trunk are attached two pairs of limbs; the lore- 

 arms in man corresponding to the fore legs of the horse or 

 dog. 



Now if we cut a fish in two, 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 beJow the backbone (Figs. 175, 

 176). In this respect the ba^^iiboned 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 



