Hypaxial muscle development.

Abstract

Chordate larvae show a surprisingly uniform “bauplan”, with a front end carrying the sense organs plus the gill and feeding apparatus, and a posterior end used for locomotion (reviewed in Goodrich 1958; Young 1962). Although adult forms frequently give up this organisation when they switch to sessile life styles, motility based on trunk muscles is maintained in acrania, and both in jaw-less and jawed vertebrates (agnathans and gnathostomes). The mesoderm on either side of the neural canal is subdivided into metameric blocks of muscle. As the notochord, and in vertebrates the vertebral column, prevent telescoping of the body, the serial action of the muscles on either side leads to an undulat..