23, 50-52) and its appendages (ib. 53-58) agree so closely with those which they have always borne as to require no explanation here. The chief surprise of the anthropotomist will be occasioned by their being included amongst the bones of the head. That the upper or pectoral extremity and its supporting arch form actually integrant parts of the occipital segment of the skull, will be proved in the memoir on the general homologies of the bones of the head. I may, here, however, in reference to the terms 'ulna' and 'radius,' request the anatomist to compare the skeletons of the perch or cod with that of the porpoise. The pectoral extremity is in the form of a fin, and in both fish and marine mammal it is applied, in a state of rest, prone to the side of the trunk; in this position it will be seen in the Delphinus, that the radius is downward, and the ulna with its projecting olecranon upwards. I take this as the guide to the homology of the two bones that support the carpal series of the pectoral fin in fishes. Cuvier, however, gives the name of 'cubital,' perhaps on account of its angular olecranoid prolongation, to the lower bone, and radial' to the upper bone and in these determinations he is followed by M. Agassiz. Both bones coalesce with the supporting arch in the lophius and some other fishes; and since, in the lophius, two of the carpal bones are unusually elongated, Geoffroy mistook these for homologues of the radius and ulna. The condition of the pelvic member or ventral fin is, in fact, here repeated in the pectoral; there being no homologous segment of thigh or leg interposed in any ventrals between the supporting (pelvic) arch and the fin-rays representing the tarso-metatarse and phalanges. The earlier stages in the development of all locomotive extremities are permanently retained or represented in the paired fins of fishes. First the essential part of the member, the hand or foot, appears : then the fore-arm or leg; both much shortened, flattened and expanded, as in all fins and all embryonic rudiments of limbs: finally comes the humeral and femoral segments; but this stage I have not found attained in any fish. It is with considerable doubt that I place, qualified by a note of interrogation, Cuvier's "troisième os qui porte la nagoire pectorale" as the homologue or rudimental representative of a 'humerus. Normally, I believe this proximal member of the radiated appendage of the scapular arch not to be distinctly eliminated from that arch in the class of fishes. The Siluroids are examples of a similar confluence of the first segment (preoperculum) of the diverging appendage of the tympanic arch with that arch. With regard to the lower, distal or apical element of the scapulo-coracoid arch, always the largest bone of the arch in fishes, Cuvier's idea that it is the humerus,' far less accords with the law of the development, the connections, and the essential nature of that bone, than the more prevalent view, that it represents the clavicle: a view entertained by Spix, Meckel, and Agassiz, by Wagner, who calls it 'vordere Schlüsselbein,' and by Geoffroy, who calls it 'furculaire.' I have, however, been induced to regard the lower element of the scapular arch, in fishes (fig. 5, 52), as homologous with that bone, the coracoid,' which progressively acquires a more constant and larger development in descending from mammals to fishes, and which is manifestly a more essential part of the arch than the clavicle, since it is more constant in its existence, and always more completely developed in birds and reptiles; and especially since it contributes more or less of the surface of attachment for the radiated appendage, which the clavicle never does. With reference, also, to the Cuvierian determination of the hæmapophysial portion of the occipital inverted arch in fishes, this is unquestionably as essential an element of the arch as is the 'coracoïde' in other vertebrates; and it is the most important part in the piscine class, in no member of which does it present the slightest approach to the character of

a diverging appendage, such as the humerus essentially is, whenever it has an independent existence. By some ichthyotomists, the bone which I call coracoid (52) has received the special name of 'cœnosteon.'

Cuvier's usual judgement and acumen seem to have been in abeyance, when, having determined the rays of the pectoral fin to represent the bones of the hand, and the two bones which support them in fishes to be those of the fore-arm, he concluded that, therefore, the great bone which completed the scapular arch "répondra donc nécessairement à l'humérus."-Hist. des Poissons, 4to. i. p. 274. The great anatomist assigns no other reason: but the arch supporting the ventral fin does not necessarily answer to the tibia or the femur, because neither of these segments are interposed between the arch and its appendage--the modified foot*. The scapula of many reptiles, especially of the batrachia, is manifestly, he proceeds to state, composed of two bones. But in those reptiles the arch is completed below by a third bone, which neither Cuvier nor any other anatomist has called 'humerus.' Now Cuvier's humerale' in fishes precisely answers to that third bone in reptiles which he rightly calls the 'coracoid' in that class.

The coracoid of fishes being thus determined, it necessarily follows that that inconstant bone, or pair of bones (58) posterior to it on each side, cannot be, as Cuvier, Geoffroy, Meckel and Agassiz have supposed, the representative of the 'os coracoïdien' of the reptile and bird. It holds, indeed, as they have said, the same relative position to the bone 52, here called coracoid, which the coracoid in the lizard and bird holds to the clavicle in those animals. But is no account to be taken of the remarkably though normally advanced position of the scapulo-coracoid arch in fishes? Granting, as I shall give evidence to prove in treating of the general homologies of the bones, that the bone (58) called by Cuvier coracoïdien' in fishes appertains to a vertebral segment posterior to the occipital one, yet in the extraordinary backward displacement which the true scapulo-coracoid arch undergoes in the air-breathing vertebrates, may not its relative position to that arch become reversed, and the part which is behind in fishes become before in birds? I entertain no unmeet confidence in the correctness of my view of the special homology of Cuvier's 'os coracoïdien' in fishes with the furculum or clavicle' of air-breathing vertebrates: the argument against such a view, from its posterior position in fishes, has not, however, the same weight with me as it appears to have had with Cuvier and his followers: and, leaving this as one of the undecided points in special homology, with the proposition of the provisional name of 'epicoracoid' (epicoracoideum, Lat.) for the bone in question, I proceed to consider other mooted points of special homology, of which there are better and surer grounds for the determination.

The first discrepancy, demanding special consideration, which meets the eye in the TABLE I. is that which relates to the determination of no. 6. The German authorities regard what I believe to be the homologue of the human 'ala major sphenoidalis' in the cold-blooded Vertebrata, to be the homologue of the pars petrosa ossis temporis. Cuvier recognises the 'grande aile du sphénoïde' in mammals, birds and fishes, but regards my alisphenoid' in reptiles as the 'rocher' or 'pars petrosa.' Geoffroy concurs with Cuvier and the German anatomists so far as to view my 'alisphenoid' in the Crocodile as a dismemberment of the petrosal, calling it prérupéal;' but he recognises, like Agassiz and Cuvier, the true alisphenoid in fishes, and with them differs in that respect from the German homologists. It does not appear that the alisphenoid has been mistaken for any other bone than the petrosal, and the * The great Linnæus indicates his appreciation of the homology of the ventral fins of fishes by styling the fishes without those fins 'Apodal.'

question to be determined, therefore, is, what are the essential characters respectively of the 'alisphenoid' and the 'petrosal' in the vertebrate series?

Those of the alisphenoid appear to me to be the following:-1st, its connection below with the basisphenoid and behind with the petrosal, where it forms the forepart of the 'otocrane' or cavity for the reception of that osseous or cartilaginous immediate capsule of the labyrinth or internal organ of hearing the alisphenoid is also commonly, but not constantly, joined before with the orbitosphenoid, and above with the parietal: it has other less constant connections with the squamosal, the exoccipital, the supraoccipital and the basioccipital: 2ndly, with regard to its essential functions, the alisphenoid protects more or less of the side of the mesencephalon, or (in mammals) of the middle lobe of the hemisphere: it gives exit, by notches or foramina, to the third, and usually, also, to the second divisions of the trigeminal or fifth pair of nerves.

The essential character of the petrosal is to envelope immediately the whole of the vascular and nervous tunics of the labyrinth or internal organs of hearing, either in a membranous, a cartilaginous or an osseous state; its histological condition being much less constant than that of the alisphenoid.

On viewing the alisphenoid on the interior surface of the human skull (fig. 6, 6), it seems to be the least significant and important part of the lateral

walls of the cranial cavity: it forms their smallest portion: it is much surpassed in extent by the squamosal (ib. 27) and the supra-occipital (ib. 3), and still more so by the enormously expanded parietal (7) and frontal (11). Nevertheless we find it connected, anchylosed indeed, below to the basisphenoid (5), bounding anteriorly the space into which the petrosal (16) is wedged; connected in front with the orbito-sphenoid (10), and usually articulating by its superior apex with the parietal: I purposely omit the mention of other connections of the alisphenoid in Man which are less constant in the vertebrate series. But it is important to observe, notwithstanding the displacement which the alisphenoid has undergone through the intercalation of the extraordinarily developed squamosal into the lateral walls