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Climax of the Animal Kingdom 

 Phylum Chordata 



This last phylum of the animal kingdom includes the largest and most 

 conspicuous animals of the kingdom and is, therefore, the best known 

 as a group. This, together with the fact that the phylum includes man, 

 generally causes us to think of it as the most important group of animals. 

 The term vertebrates is almost synonymous with chordates because the 

 great majority of the chordates are vertebrate animals. 



Chordate Characteristics 



The chordates include such a variety of animals that it would seem 

 rather difficult to list generalized characteristics that apply to all. This 

 phylum includes such animals as elephants, fish, snakes, and birds and, 

 at first glance, such an assortment would seem to have very little in 

 common. However, there are certain morphological features that all 

 possess. 



A Dorsal Tubular Nerve Cord. The nerve cord runs the length of 

 the body against the dorsal body wall in contrast to the ventral nerve 

 cord found in the higher invertebrates. Embryologically this cord is 

 formed from a strip of ectoderm lying on the dorsal surface of the em- 

 bryo. This strip first sinks inward to form a groove and then the upper 

 walls of the groove come together and fuse, forming the tube. The ante- 

 rior part of the tube enlarges to form the brain, whereas the remainder 

 forms the spinal cord which retains its tubelike characteristics through- 

 out the life of the animal. 



A Notochord. Just under the spinal cord is a flexible tube-like body 

 which is called the notochord. The phylum name is taken from this 

 characteristic. In the higher chordates the notochord is present in the 

 embryo only, since it is replaced by the bony vertebral column in the 

 adult form. In the center of each intervertebral disc of man, however, 

 there is a vestige of the notochord which helps to make this disc more 

 resilient. 



A Post-anal Tail. A part of the body, containing the notochord or 

 vertebral column, projects beyond the anus to form a tail at some time 



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