Editing Skull (section)

====Fish====
[[File:FishKeyDay.jpg|thumb|upright=.8|Fish head parts, 1889, Fauna of British India, Sir Francis Day]]

The skull of fish is formed from a series of only loosely connected bones. [[Lamprey]]s and [[shark]]s only possess a cartilaginous endocranium, with both the upper jaw and the lower [[jaw]]s being separate elements. Bony fishes have additional [[dermal bone]], forming a more or less coherent [[skull roof]] in [[lungfish]] and [[holost]] fish. The lower jaw defines the chin.

The simpler structure is found in [[jawless fish]], in which the cranium is normally represented by a trough-like basket of cartilaginous elements only partially enclosing the brain, and associated with the capsules for the inner ears and the single nostril. Distinctively, these fish have no jaws.<ref name="VB2" />

[[Cartilaginous fish]], such as sharks and rays, have also simple, and presumably primitive, skull structures. The cranium is a single structure forming a case around the brain, enclosing the lower surface and the sides, but always at least partially open at the top as a large [[fontanelle]]. The most anterior part of the cranium includes a forward plate of cartilage, the [[rostrum (anatomy)|rostrum]], and capsules to enclose the [[olfactory]] organs. Behind these are the orbits, and then an additional pair of capsules enclosing the structure of the [[inner ear]]. Finally, the skull tapers towards the rear, where the foramen magnum lies immediately above a single [[Condyle (anatomy)|condyle]], articulating with the first [[vertebra]]. There are, in addition, at various points throughout the cranium, smaller [[Foramina of skull|foramina]] for the cranial nerves. The jaws consist of separate hoops of cartilage, almost always distinct from the cranium proper.<ref name="VB2">{{cite book |last1=Romer |first1=Alfred Sherwood |first2=Parsons |last2=Thomas S. |year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location= Philadelphia, PA |pages=173–177 |isbn= 0-03-910284-X}}</ref>

[[File:Xiphias gladius 7zz.jpg|thumb|left|Skull of a [[swordfish]]]]

In [[ray-finned fish]], there has also been considerable modification from the primitive pattern. The roof of the skull is generally well formed, and although the exact relationship of its bones to those of tetrapods is unclear, they are usually given similar names for convenience. Other elements of the skull, however, may be reduced; there is little cheek region behind the enlarged orbits, and little, if any bone in between them. The upper jaw is often formed largely from the [[premaxilla]], with the maxilla itself located further back, and an additional bone, the symplectic, linking the jaw to the rest of the cranium.<ref name="VB"/>

Although the skulls of fossil lobe-finned fish resemble those of the early tetrapods, the same cannot be said of those of the living [[lungfish]]es. The [[skull roof]] is not fully formed, and consists of multiple, somewhat irregularly shaped bones with no direct relationship to those of tetrapods. The upper jaw is formed from the [[pterygoid bone|pterygoid]]s and [[vomer]]s alone, all of which bear teeth. Much of the skull is formed from [[cartilage]], and its overall structure is reduced.<ref name="VB" />