Skeletal Anatomy: Axial & Caudal
The axial skeleton of vertebrates is structured around the notochord, a tough, elastic, gel-filled tube. Pairs of segmental arcual elements, the basidorsals, interdorsals, basiventrals and interventrals, wrap around the notochord. In later sharks, bony fish and tetrapods, the notochord is constricted or obliterated by growth of solid vertebral centra. The main nerve trunk of the body lies above the notochord and is protected by pairs of neural arches. Neural spines, that may be either paired or median, usually attach to the neural arches. In the caudal area of the body, paired hemal arches surround blood vessels, and median hemal spines are attached to the arches. Median fins are supported by median segmental elements.
The caudal skeleton is upturned (heterocercal) in primitive gnathostome fish. Hypural elements, enlarged hemal spines, support the fin radials of the tail.
intro | head | pectoral fin | pelvic fin | axial | caudal