P3.180 Friday, Jan. 6 The morphology of the myomere-myoseptal intersections in a lamprey (Petromyzon marinus) and a shark (Squalus acanthias) WOOD, B.M.*; ANDERMANN, R.J.; HOMBERGER, D.G.; Louisiana State Univ., Baton Rouge ; Louisiana State Univ., Baton Rouge ; Louisiana State Univ., Baton Rouge email@example.com
An accurate anatomical description of the myomere-myoseptal intersections in the axial musculature of piscine vertebrates is a necessary basis for a mechanical explanation of how contractile forces are transmitted from one myomere to the next via myosepta. As a first step, the superficial muscle fiber bundles were analyzed through microdissection at their intersection with myosepta in the trunk region. In the lamprey, the tendons of myomeric muscle fiber bundles join a myoseptum on each side, but in opposite directions, at shallow to right angles (depending on the curvature of the myoseptum). In the shark, the tendons of myomeric muscle fiber bundles traverse a myoseptum to connect mainly to muscle fiber bundles directly across, but separate slips of tendons connect to muscle fiber bundles diagonally across. These observations suggest that, at least in the superficial axial musculature of lampreys and sharks, muscle fiber bundles do not terminally attach to myosepta. Hence, contractile forces of the superficial muscle fiber bundles may be transmitted to one another across the myosepta. These observations show that the structural and mechanical relationships between the myosepta and myomeres deserve to be analyzed in depth. Furthermore, a realistic (“realitätsgetreues”) biomechanical model of the myomeric-myoseptal intersections may provide information for a more complete understanding of (1) the interactions between the central nervous system and the axial musculature; (2) the evolutionary changes in the axial musculature of Petromyzontiformes and Chondrichthyes; and (3) the evolutionary history of early fishes.