| In vertebrates finally, the organization of muscles into myotomes for swimming has long been considered of crucial adaptative importance. |
| Pikaia has myotomes and what looks like a notochord, indicating that it is a chordate, but only its shape suggests that it is a lancelet rather than a fish. |
| In fishes, small outgrowths from the myotomes enter the limb rudiment to form the muscles of the fins. |
| All these muscles belong to the fifth cervical to first thoracic myotomes. |
| This segmentation also extends to the nerves that supply the myotomes and to some body cavities, excretory structures, and other parts. |
| The fins, both median and paired, obtain their musculature by the ingrowth into them of muscle buds from the adjoining myotomes. |
