Meeting Abstract
Fishes in the order Cypriniformes are characterized by having a sesamoid bone in the upper jaw called the kinethmoid. The kinethmoid is attached to the maxillae, premaxillae, palatines, and neurocranium by ligaments that are responsible for transmitting muscular forces to protrude and retract the jaw during feeding. Each ligament is composed of differing types of connective tissues, and we examined the morphology and composition of the tissues from a functional perspective. We used histology to describe the morphology of the elements in the upper jaw of four cypriniform species, the goldfish, Carassius auratus, zebrafish, Danio rerio, rosy minnow, Pimephales promelas, and tiger barb, Puntigrus tetrazona. Using both quadruple and quintuple staining methods, we were able to identify the structure of the kinethmoid and ligamentous connections in addition to the types of cartilage-like connective tissues present. The premaxillary ligament is composed of hyaline-cell cartilage, a tissue with densely packed cells and little extracellular matrix. Both the palatine and maxillary ligaments resemble mammalian ligaments by having fusiform-shaped cells in a matrix with parallel fibers, but the palatine ligament extends more rostrally during protrusion and contains elastin, which may function to retract the jaws. Additionally, the kinethmoid stains differentially for both high and low tensile collagen where the low tensile region is located towards the interior of the bone while the high tensile region is on the periphery. Through our research, we can work towards a more complete understanding of the biomechanics of kinethmoid-mediated premaxillary protrusion.
