(1696). The articulation between every fin-ray and the corresponding interspinous bone forms a hinge-joint, so as to allow of the elevation or depression of the fin. The structure of this joint is very beautiful: the two lateral halves of the ray separate, so as to form two branches, which firmly embrace the sides of the head of the interspinous bone, and terminate in little prominent tubercles which are received into corresponding lateral depressions in the bone to which the ray is attached. Sometimes, indeed, the head of the interspinous bone is completely perforated, and then the two branches of the fin-ray passing through the opening become firmly united with each other, forming a kind of joint which is peculiar to Fishes, and exactly resembles the mode of union between two links of a chain. This structure is beautifully exhibited in the articulation of the elongated rays attached to the head of Lophius jpiscatorius*.

(1697). The composition of the skull of Fishes is one of the most difficult studies connected with their history; nevertheless it is a subject of very considerable importance, and has recently occupied the attention of the most celebrated Continental anatomists. It is not by any means our intention to engage our readers in discussing all the conflicting, and sometimes visionary, opinions entertained by different authors relative to the exact homology of the individual bones forming this part of the skeleton; and we shall therefore content ourselves by placing before them, divested as far as possible of superfluous argumentation, Cuvier's1 masterly analysis of the labours of the principal inquirers concerning this intricate piece of anatomy, taking the Perch as a standard of comparison 2.

(1698). The head of a Fish may be conveniently divided, for the purpose of description, into several distinct regions, each of which will require separate notice.

(1699). The cranium, which forms the central portion of the skull, contains the brain and auditory apparatus, and constitutes the basis whereunto the other parts are connected. It is remarkable from the number of distinct pieces of which it consists, inasmuch as in Fishes the elements, or ossific centres, of which the cranial bones of higher animals are composed remain here permanently separated, overlapping each other, so as to form squamous sutures, but never becoming fused together, as the elements of the human skull invariably do at a very early period.

* Vide Yarrell's History of British Fishes, vol. i. p. 271. 8vo.

1 Cuvier et Valenciennes, Histoire des Poissons, vol. i. 4to.

2 Those who would enter more fully into the discussions relative to the essential composition of the skull are referred to the works of Greoffroy St.-Hilaire, Spix, Rosenthal, Meckel, Bakker, Bojanus, and Oken, the great disputants upon this subject.

(1700). No fewer than twenty-six bones enter into the composition of the cranium we are now considering; to which, as is now generally allowed, the following names are applicable.

(1701). The frontal bones are each divided into three portions, called respectively the principal frontal (l)*, the anterior frontal (2), and the posterior frontal (4).

(1702). Between the anterior frontal bones is the ethmoid, a simple vertical lamella, which is often merely a cartilaginous plate.

(1703). The middle of the base of the cranium is made up of two bones: - the basilar (fig. 312, 5), a portion of the occipital, forming the body of the occipital vertebra; and the body of the sphenoid (6), a distinct bone, which is prolonged anteriorly into a lengthened process, which serves as the base of the membranous septum between the orbits.

(1704). The parietal bones (7) are placed behind the posterior frontal; but they do not generally touch each other, being separated by an interposed bone called the interparietal (8).

(1705). The occipital bone is made up of five portions: namely, two external occipitalis (9), two lateral occipitals (10), and the basilar bone (5), already noticed, by which the head is articulated with the first vertebra of the spine.

(1706). Two detached bones, which represent the great or temporal alee of the sphenoid, fill up the space between the body of the sphenoid and the posterior frontal.

(1707). Two other pairs of bones, which are elements of the temporal bone in Man, likewise assist in forming the cranium: these are called the mastoid bones (12) and the petrous bones (13).

(1708). A single bone, analogous to the anterior portion of the body of the human sphenoid, and which, as will be fully evident hereafter, is essentially distinct from the posterior portion, bears the name of the anterior sphenoid, while the orbital aloe of the sphenoid are found in the two bones marked 14.

(1709). These, therefore, together with the representative of the vomer (16), complete the cranial portion of the skull; no fewer than six azygos and twenty pairs of bones entering into its composition.

(1710). Bones Composing The Upper Jaw

The upper jaw consists of two pairs of bones, which, from the looseness of their connexion with the other bones of the face, are endowed with considerable mobility.

* In order to simplify the subject as much as possible and prevent unnecessary repetition, the reader will observe that, throughout all the figures connected with the osteology of the Vertebrata, corresponding bones are indicated by the same numbers.

(1711). The Intermaxillary bones (17) form the greater part of the margin of the jaw, and are attached by a moveable articulation to the anterior extremity of the vomer. These bones are armed with numerous sharp teeth.

(1712). The maxillary bones (18) are moveably articulated with the last, and generally are in like manner furnished with teeth. In some cases they are divided into two or three pieces.

(1713). Bones Of The Face

The bones of the face in Pishes are very numerous; but, as they are of little importance to the osteologist, a bare enumeration of them will answer our present purpose, and enable the student to recognize them with facility. We have first the nasal bones (20); then a chain of bones of variable size and number (19), so disposed as to form the lower boundary of the orbit, and hence named suborbital bones. Behind these, again, a similar chain of ossicles is not unfrequently met with, arching over the temporal fossa; and these, which are apparently peculiar to Pishes, are named the supratem-poral (21).