In chondrichthyans, there is little to no bone. The dermatocranium is absent, so the chondrocranium has been expanded over the top of the head in order to form the braincase. So in chondrichthyans, the chondrocranium is the prominent part rather than in other species. The anterior of the orbital, the posterior of the oticooccipital and the ethmoid are merged into the single braincase. The splanchnocranium is also present in chondrichthyans. In the ancestors of these fish, six gill arches are places behind the mandible. The palatoquadrate, the upper jaw, of primitive sharks had been supported by the braincase and also the hyomandibula. Today sharks lack that strong connection between the hyomandibula and the palatoquadrate and instead they are suspended by the ceratohyal and Meckel’s cartilage using a very strong ligamentous connection. The skull performs a multitude of functions. It mainly protects and supports the brain and the sensory receptors. Its helps keep the brain form getting to hot in some environmental conditions. It fixes the distance between the eyes in order to allow vision, and fixing the position of the ears to permit sound localization, to tell the direction and distance of sounds. In some vertebrates, such as horned…show more content… It consisted of basal elements and packed radicals that supported the fins. In more evolved sharks, the basal components of the pectoral and pelvis girdles stretched across the midline of the body to bond into a “U” shaped scapulocoracoid and puboischiac bars. The earliest chondrichthyans show that there is no connection between the dermal contributions to the shoulder girdle. Today’s sharks have three enlarged pterygiophores at the base of its pectoral fins called metapteryguim, mesopteryguim and propteryguim. The metapteryguim part within the pelvic fin consists of a postaxial series, with one long element supporting
