ORDER IV. CARTILAGINEI.
(Cartilaginous Fishes.)
The largest and most formidable of all fishes are found in this Order. “The peculiar structure of their skeleton, which gives rise to their name, admits of these animals continuing to grow as long as they live; the consequence of which is, that as they inhabit the wide ocean, and have few enemies, they are sometimes met with of such an enormous size that their weight and dimensions are almost incredible.”[1]
The great essential character of the Order is the nature of their skeleton. Their bones have but a very small quantity of earthy matter in their composition; and what is present is deposited in grains, and not in distinct fibres. The skull is not divided into separate bones, but is formed in a single piece; yet ridges, furrows, and holes on its surfaces, enable the anatomist to discover the portions, which in other fishes are distinct, though here soldered, as it were, together. Even bones, that in other fishes constitute moveable joints, are not always distinct in this Order; the vertebræ or joints of the spine, for example, are, in some of the Rays, united into a single mass; and in other genera, some of the bones of the face are quite wanting. The bones of the jaws, known to anatomists under the names
- ↑ Swainson, Nat. Hist. of Fishes, i. 118.
