The myomere‐myoseptal intersections in a lamprey ( Petromyzon marinus ) and a shark ( Squalus acanthias )

An accurate description of the myomere‐myoseptal intersections of 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. In a lamprey, the tendons of superficial muscle fiber bundles join a myoseptum on each side, but in opposite directions, at shallow to right angles. In a shark, the tendons of superficial muscle fiber bundles traverse a myoseptum to connect to muscle fiber bundles partly directly across and partly diagonally across. Hence, contractile forces of the superficial muscle fiber bundles may be transmitted to each other across the myosepta. The construction of an accurate biomechanical model of the myomeric‐myoseptal intersections may be relevant for a range of questions, such as those pertaining to (1) the biomechanics of serially arranged contractile systems that are also found in the apterial and feather muscles of birds and the sarcomeres of myofibrils; (2) the interactions between the central nervous system and the axial musculature during undulatory locomotion; and (3) the evolutionary changes in the axial musculature of Petromyzontiformes and Chondrichthyes. Funding: LSU Foundation to DGH. Grant Funding Source : N/A