Skeletal Anatomy: Head
The head skeleton of a fish consists of three components, the neurocranium (braincase), the suspensorium (jaws plus whatever other structures suspend them from the neurocranium), and the branchial skeleton (holds the gills).
The neurocranium protects the brain and the special sense organs, the olfactory, organs, eyes, and senses of hearing and balance.
The jaws are involved in feeding. The type of suspensorium helps to determine the flexibility and bracing of the feeding system and thus the basic limitations on feeding mode. The nature of the suspensorium is one of the most important criteria in the determination of relationships among major groups of fish.
The branchial skeleton consists of many movably joined bones that support the respiratory system. It is rarely preserved intact in fossil fish, but can be seen to display several remarkably different configurations among the different fish.
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Autodiastylic Euchondrocephalan head (Debeerius ellefseni). Palatoquadrate articulates with basitrabecular process and ethmoid part of braincase. This is the basic type of jaw suspension in the gnathostomes. The jaw suspension of all vertebrates can be derived from this type. |
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| Hyostylic Elasmobranch (shark) head. The palatoquadrate hangs from the hyomandibula and the ethmoid part of the braincase. |  |
| Holostylic Holocephalan (chimaeroid) head. The palatoquadrate is fused to the braincase; the hyoid arch is primitive in that it does not contain a hyomandibula. |  |
| Amphistylic Elasmobranch (shark) head. The palatoquadrate articulates with the postorbital process of the braincase (as does the hyomandibula) and the ethmoid part of the braincase. |  |
| Met-hyostylic Paleoniscoid actinopterygian head. The palatoquadrate is sutured to the hyomandibula and articulates to the ethmoid part of the braincase. Braincase, palatoquadrate, hyoid and branchial arches are ossified, and the head is sheathed externally in bones. |  |
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