Fig. 47.—Shoulder-girdle of a Flounder, Paralichthys californicus (Ayres).
The pelvis, remote from the head, is formed, in the shark, of a single or paired cartilage with smaller elements at the base of the fin-rays. In the males a cartilaginous generative organ, known as the clasper, is attached to the pelvis and the ventral fins. In the Elasmobranchs the tail vertebræ are progressively smaller backward. If a caudal fin is present, the last vertebræ are directed upward (heterocercal) and the greater part of the fin is below the axis. In other forms (sting-rays) the tail degenerates into a whip-like organ (leptocercal), often without fins. In certain primitive sharks (Ichthyotomi), as well as in the Dipnoi and Crossopterygii, the tail is diphycercal, the vertebræ growing progressively smaller backward and not bent upward toward the tip.
In the chimæras (Holocephali) the notochord persists and is surrounded by a series of calcified rings. The palate with the suspensorium is coalesced with the skull, and the teeth are grown together into bony plates.
Fig. 48.—Shoulder-girdle of a Toadfish, Batrachoides pacifici (Günther).
Fig. 49.—Shoulder-girdle of a Garfish, Tylosurus fodiator (Jordan and Gilbert).
The Archipterygium.—The Dipnoans, Crossopterygians, and Ganoids represent various phases of transition from the ancient cartilaginous types to the modern bony fishes.