VERTEBRATE ANIMALS 



OF THE 



UNITED STATES 



VERTEBRATES 



Vertebrates are bilaterally symmetrical animals with an interna 

 cartilaginous or bony skeleton; with usually two pairs of locomotory 

 appendages, the fore and hind limbs; with pharyngeal respiration; with 

 a tubular dorsal central nervous system; with a ventral heart, a closed 

 circulatory system consisting of arteries, capillaries, and veins, and red 

 blood. 



The vertebrates are characterized as a group among animals by 

 their large size and the high degree of specialization of many of their 

 parts, and also by their general distribution over the earth. Every 

 part of the surface of the globe, as well as the ground and the waters 

 beneath and the air above it in which animals can in any way satisfy the 

 need of all life of food and oxygen, is inhabited by them. The fishes 

 and other aquatic forms abound in fresh and salt water, while the 

 terrestrial and flying vertebrates inhabit all the continents, even the 

 coldest and most inclement. 



External Characters. — The vertebrate body is in most cases more 

 or less cylindrical in form, and is made up of four regions, the head, the 

 neck, the trunk and the tail. The head, being the anterior portion of 

 the body, bears the principal organs of orientation, which are the special 

 sense organs, and the organs of prehension — the mouth with the lips 

 and teeth where these are present; it also contains the large brain, which 

 innervates these essential organs, enclosed, for its protection, in the 

 skull. The neck is absent or unimportant in fishes and other aquatic 

 vertebrates, but in most of the land forms is of great importance 

 inasmuch as it is the flexible body region which gives the head the wide 

 range of movement necessary to it in a rapidly moving terrestrial 

 animal. In fishes the head and anterior portion of the body forms a 

 wedge which must be pushed by the locomotory movements of the 

 tail-fin through a resistant medium, and it is greatly to the advantage 



