Meeting Abstract
Two collagenous structures, the ventral penile tendon (VPT) and the ligamentum rami (LR), are critical to normal phallic eversion and retraction in male American alligators (Alligator mississippiensis). Both structures connect the phallus to the ischium, but they have different functional roles. The VPT anchors the phallus in the cloaca and acts as a fixed point around which the phallus rotates during eversion and retraction; the paired LR are thought to act as a spring that returns the phallus to its resting orientation after eversion. Tensile tests of both tissues indicate that although both the VPT and the LR have a J-shaped stress-strain curve characteristic of collagenous tissues, the LR are more extensible than the VPT and have a Young’s modulus that is approximately an order of magnitude greater. Histological examination reveals that both the VPT and LR are primarily made up of Type I collagen fibers but the arrangement of collagen inside the tissue differs. Collagen fibers in the LR are long and arranged parallel to the long axis of the structure, while collagen fibers in the VPT are shorter and arranged in an interconnected three-dimensional network. The differences in the mechanical behavior of the VPT and LR during penile eversion and retraction may therefore be the result of differences in collagen fiber arrangement within each tissue rather than differences in material composition.
