In some families, as in the 2Ifurtenida, part of the anterior vertebra have a little crest or vertical apophysis developed from beneath the body. Other races have a portion of the bodies of their vertebra soldered together: a this there are examples among the Cyprim'cla, Fistularida, and Silurida.
Those vertebra which are situated above thel abdominal cavity have transverse processes de-II veloped to a greater or less extent. These, ini some instances, as, for example, in the Cy-1 prinidze, remain for a long time only attached by suture to the bodies of the vertebrT, frorn which they are easily distinguished.
In certain Fishes, as, for example, in Merlus, the tmnsverse processes are very large and give attachment to the swimming bladder. Some times the ribs are suspended from the trans verse processes, or sometimes they are derived immediately from the bodies of the vertebrx. In this respect there are great varieties.
In those vertebra that are situated behind the abdominal cavity there is an inferior fora men for the lodgement of the great blood vessels of the trunk bounded by inferior spinal ( hemapophyses), and, like the superior, generally supporting long spinous processes, (fig. 493, 5,) so that the vertebra seem to consist of similar parts, both above and below the body.
These inferior arches of the caudal vertebra are considered by Cuvier as being formed by the inordinate developement of the transverse processes, which he describes as here becom ing directed downwards and united to each other, so as to form the inferior ring ; and, certainly, in the generality of Fishes, by tra cing the apparently gradual conversion of the abdominal into the. caudal vertebrx, such is the conclusion at which the comparative anato mist would naturally arrive. In many Fishes, however, as, for example, in the Muranidw, these inferior arches with their appropriate spines are in the caudal region co-existent with distinctly developed transverse processes, evi dently shewing that they must be regarded as being totally different elements of the skeleton, namely, the hwmapophyses. (See OSSEOUS SYSTEM.) The inferior or hmmapophysial elements, like the superior arches, have in many instances oblique processes developed from them, which in some cases are very large and branched, so as to form a kincl of interlacement around the vascular canal. This is especially observable in certain Tunnies.
As the vertebra approach the tail, their pro cesses are gradually shortened, and the verte bral canal becomes narrowed or obliterated, (fig. 493, 8,) and at length the terminal vertebra
have their apophyses consolidated with each other and with the interspinous bones, so as to form in some Fishes, as the Perch, a vertical triangular plate, to the posterior margin of which are articulated the rays of the caudal fin (9). In Fishes with long and pointed tails like the Eels this disposition is wanting; but in other races, such as the Pike, the real composition of this part of the skeleton is easily recognisable.
Ribs and sternum.—The ribs of Fishes have nothing to do with respiration, merely serving to support the muscular parietes of the body ; they consist of the dorsal portion only, which is articulated by a _single head, either to the transverse processes or to the bodies of the vertebrm themselves. Frequently they give off long bony processes, which penetrate among the muscles; and sometimes also similar pro cesses are attached above the ribs to the bodies of the vertebr themselves, so that the flesh of -some Fishes appears full of little bones as fine as hairs. The ribs vary extremely in different genera. Sometimes they are round and slen der, sometimes compressed and falciform ; occasionally they seem to surround the whole abdomen, and in many species are quite rudi mentary or altogether wanting. The sternum is entirely deficient in most Fishes; sometimes, however, it does exist, as in Clupea, Vomer, &c.; in such cases it consists of a longitudinal series of impair bones, differently shaped in different genera, to the sides of which the ribs are attached inferiorly.
Cronium.—The cranium of osseous Fishes, when all its parts are completely developed, is rnade up of no fewer than twenty-six bones, six of which are azygos, viz. the basilar,the principal sphenoid, the anterior sphenoid, the vorner, the ethnwid, and the interparietal or superior occi pital ; and twenty are in pairs, namely, the frontal, the anteriorfrontal, the posteriorfron tal, the parietal, the mastoid, the external occi pital, the lateral occipital, the petrous, the great alar and the lesser alar bones ; but as these have all been described and figured in a pre ceding article, and their homologies with the cranial bones of the other vertebrate classes fully discussed, (vide OSSEOUS SYSTEM, Comp. Anat., vol. iii. p. 826,) it would be superfluous to dwell upon them more at length in this place.