But the frontal bone does not entirely form the lower surface of the ceiling of the orbit ; the anterior part is formed by a flat and irregu lar bone, covered above, like the frontal, by the maxillary ; this, which is the jugal bone, gives off from its anterior angle a slender and long apophysia, which is directed backwards, and proceeds to articu late itself to the zygomatic apophysis of the temporal bone : this deli cate filament is the sole bony limit of the orbit below. The zygomatie apophysis of the temporal bone unites itself to the postorbital apo physis of the frontal, in order to limit the orbit backwards ; whence it happens that the whole zygomatio arch properly so called appertains to the temporal bone, which last extends but little into the temple, and terminates at the temporal crest, so that it does not appear in the occiput. Below, the lateral occipital and the basilary bones produce projecting plates, which, uniting to the continuation of the ptery goidean ala and to a lamina of the temporal bone, compose a sort of vault, under which are suspended by ligaments the petrous and tym panic bones, which are promptly conjoined into one piece. The parietal bone, after having passed behind the temporal, forms a part of this vault. The temporal bone itself therefore seems to be almost foreign to the composition of the cranium, only serving to stop some small holes remaining in the parietal. This, Cuvier observes, is the commencement of the separation which it undergoes in the inferior classes. The part of these crests which borders the basilary region on each side makes this region resemble a wide canal. At the bottom of the orbit are seen the two sphenoid* placed as ordinarily—the posterior touching the temporal, the parietal, and the frontal ; the anterior touching the posterior, the frontal, and the internal pterygoid apophysia : but the great peculiarity is the form of the back nostrils. The maxillaries being prolonged into a flattened muzzle, and the teeth terminating in front of the orbit, the maxillary is not on the floor nor on the anterior or lateral walls of that cavity, but at its ceiling, as is also the jugal bone : it completes the internal border of this ceiling. From the entire posterior contour of the lower surface or palatine of these maxillary bones rises a sort of quadrangular pyramid, whose base is traversed vertically by the nostrils, and in which the rest of the apace is hollow, or contained between two laminas open behind. These form a sort of double walls, which surround the posterior aper ture of the nostrils. They are composed of the palatines and the pterygoid internal apophyses. Each palatine is folded back on itself in an irregular ring to form the base of this double wall, and the ceiling is completed by the maxillary to which it is articulated. The internal pterygoid apophysih is only recurved in the form of S. One of its curvatures articulates itself externally to the palatine to prolong the lower and external wall ; the other unites to the other arch of the palatine, and afterwards continues on the anterior sphenoid to articulate itself to the vomer, and thus complete the internal part of this entourage of the back nostril ; whence it results, that the entire border of the back nostril, except the vomer, belongs, as in the Ant Eaters, to the interval pterygoid apophysis. The great sinus inter cepted between the two walls of this border is a peculiarity in the Dolphin : this internal pterygoid always remains distinct. The poste rior sphenoid is conjoined with the basilary much sooner than to the anterior sphenoid : Cuvier even found it conjoined in some feetuses before any of the other bones. This nearly absolute derangement of the bones has, Cuvier observes, much changed the direction of the boles. In place of the incisive hole there is a long canal, which pro ceeds between the two maxillaries and the two intermaxillaries, from the end of the muzzle to the nostrils, near which it bifurcates. The suborbital hole is to be sought in the ceiling of the orbit, where it represents a cavity open below, from which proceed in different direc tions canals which go to open on the superior surface of the maxillaries and intermaxillaries, not below but above and opposite to the orbit. Cuvier could find neither lachrymal bone nor hole. In a hollow in front of the orbit, between the maxillary, the vomer, and a point of the palatine bone, is a small hole which ascends in the nostril and represents the splieno-palatine. To respond to the pterygo-palatino, Cuvier could only perceive a small hole on the junction of the palatine to the maxillary in the palate, which enters the sinus placed on each side of the posterior nostrils. The optic hole Is moderate and in the anterior sphenoid as ordinarily. The apheno-orbital hole between the two sphenolds also performs the office of the round hole. There is an oval hole in the posterior sphenoid, and more internally in the same bone a hole for a vessel. An aperture between the temporal, the
lateral occipital, the basilary, and the posterior sphenoid gives passage to the nerves of the car to go to the petrous bone. In front of it, and very near, Is the carotldean hole. In the basilary bone, and in a notch of the borders of this vault of the ear, is the condyloidean hole, which is very small. It is the posterior border of this vault which occupies the place of the mastoid apophysis.
Internally the cerebral cavity in very remarkable, inasmuch as its height surpasses its length. The floor Is very compact. The Bella is but slightly marked. The cerebelLy fosses are the most hollowed ; there is often a very projecting bony tentorium in its middle ; the fals is always bony backwards, but it has no crest, and some small holes are scarcely perceptible in the cribriforin plate. The petrous and tympanic bones are not joined to the cranium by any suture, and are not even inclosed, but only suspended by ligaments under the sort of vault above noticed. They unite at an early period into a aingle bone of the ear. The occipital condyles are large, but project little. The hole, directed entirely in the line of the head, is nearly circular.
Cuvier remarks that complete symmetry is never found in the skulls of Dolphins; the two nostrils, the two nasal bones, and the adjacent parts, never appeared to him equal, as in other manuniferous animals; and this, he observes, conducts us to the extreme inequality of those parts in the Cachalots.
The various species of Dolphins differ from each other in the relative length and width of the muzzle, the number of teeth, and the divers convexities or concavities of their parts, the palate, dm. Cuvier points out these variations in the species, and particularly notices the Dolphin of the Ganges (Susuk) as the most extraordinary in the structure of its cranium.
In the common Dolphin the seven cervical vertebra" are united in a single body, and so they are in the Porpesse; but this is not univer-. sally the case, for in the Dolphin of the Ganges, for instance, the cervical vertebra) are as distinct as in any quadruped. But where they are anchylosed, as in the common Dolphin, the atlas is fully developed, and has sufficiently strong, transverse, conic apophyses. The body of the axis is very delicate; but its spinous apophysis, anchylosed to the atlas, is also well marked. The four succeeding vertebras arc, to use Cuvier's expression, as thin as paper, and their annular part unites above to the lower surface of the spine of the axis. The seventh cervical has some volume and rather strong distinct apophyses. The dorsal vertebra are 13 in number, and there are 13 ribs. The first three ribs only have a head and a tubercle, and are articulated on the body of two vertebrae end on the extremity of the transverse apophysis of one of them. The ten succeeding ribs are only articulated to the extremity of the trausverse apophysis. The last cervical and the first six dorsal have their articular apophyses united to each other by horizontal surfaces, the anterior of which is above. At the sixth they begin to become oblique ; at the seventh they are nearly vertical. Commencing with the fourth, the transverse apophysis gives off a small point from its anterior border. This point approaches the anterior articular apophysis, and becomes blended with it at the seventh ; afterwards these points form the only articular apophysis; those of one vertebra embracing the lower part of the spinous apophysis of the preceding vertebra. Towards the twenty second vertebra or the second lumbar they no longer reach it ; but they remain irregularly marked far upon the tail. The transverse apophyses of the lumbar region are very long, and the spinous very high. On the tail they are shortened ; the spinous are widened ; and the transverse are directed rather forwards. They disappear at the forty-ninth vertebra, and the spinous at the fifty-first or tifty-second. The V-shaped bones (latemapophyses of Professor Owen) of the under part of the tail commence under the thirty-eighth. Tho body of the vertebrae are round, rather angular below ; more compressed and thicker in the region of the back ; shorter in the lumbar region and in that of the tail, where they present a kind of carination below. Tho anterior and posterior epiphyses remain a long time distinct. The sternum is composed of three bones; the first, very wide, is notched in front, and gives off on each side between the first and second rib a sharp point directed backwards. There is a hole in the middle. The second is simply rectangular. Between the filet and it the second rib is articulated ; the third rib is attached between the second and third bone, which receives on its sides the fourth, and towards its point the fifth and sixth, which is the last true rib. Tho sternal parts of the ribs are all ossified.