The Notochord: Ancient Forerunner of the Vertebral Column Help
Introduction to The Notochord: Ancient Forerunner of the Vertebral Column
Only within the last 500 million years or so have there been any chordates ( KOR -dates) – animals with some kind of “chord” or “cord” present to stiffen their backs. It is this later group, called the Phylum Chordata (kor- DAY -tuh), to which we now turn with interest.
It is very reasonable for you, the reader, to ask, “Just what is meant by having a chord or cord in your back?” This concept is best explained by looking at Figure 12.1, which provides the general body plan of a primitive chordate. This figure shows the four general characteristics of all chordates:
1. The presence of a slender notochord ( NO -tuh-kord) running down the back during at least part of the life cycle;
2. A hollow nerve cord that lies immediately dorsal to the notochord;
3. Gill slits along each side of the head; and
4. A post-anal ( AY -nul) tail that is very muscular.
The notochord is the key anatomic feature. It is a long, narrow structure in the “back” (noto-) that looks like a thin “cord” (chord) or rod. The noto-chord’s chief function is supporting and stiffening the body. All chordates have a notochord in their bodies during at least one stage of their development. And it is this notochord that can serve as the basis for development of a full vertebral column or “jointed backbone.”
Practice problems for these concepts can be found at: Chordata Test
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