of the tympanic cavity; this last has its frame complete. The ossiculum passes by means of a hole to enter the second chamber of the cavity, which, as in the other tortoises, is closed behind by a cartilage only. The Eustachian tube commences by a notch of the posterior border, as in the Land Tortoises. The spine of the occiput and the mastoïdean tuberosities are all three pointed, and project more backwards than the articular condyle. The space occupied by the tympanic cavity at the posterior border of the temporal fossa is very narrow, but it widens in descending again towards its apophysis for the lower jaw. The temporal ala is placed below and in front of the great hole of the fifth pair of nerves, and the descending part of the parietal bone articulates itself in front of it to the internal pterygoïdean. It therefore enters more into the composition of the cranium, and is more easily recognised, than in the other tortoises. wants the bony vomer, so that its two back nostrils form but one aperture in the skull. Its palatines want the palatine portion. The frame of the first chamber of its tympanic cavity is complete; this chamber communicates only by one narrow hole with the mastoïdean cellule, and the Eustachian tube takes its origin there by means of a slit, which is an extension of the hole by which the ossiculum passes into the second chamber." The temporal bone is covered, as in the turtles, by the parietal, temporal, jugal, and posterior frontal bones. This last is very narrow; it has one portion descending into the temple, which, uniting to an ascending part of the palatine bone and to a re-entering portion of the jugal bone, forms a partition which separates the orbit from the temporal fossa, not leaving any communication except one great hole near that descending part of the temporal bone which replaces the temporal ala. The pterygoid unites itself forward with the palatine and jugal bones, and not with the maxillary, Cuvier found no osseous trace of the anterior sphenoid, which does not reach so far backwards. Its external bor- nor of its alæ; a rather delicate membrane occupies its der is re-curved with the neighbouring portion of the jugal place, and closes on each side the front of the cerebral bone, and thus forms in the lower part of the temple a cavity. kind of canal, which takes its commencement at the hole The principal character of the Marine Tortoises, or Turof communication of the temple with the orbit. Its pos- tles (Chelonians as they have been generally termed), is, terior angle on the contrary is directed a little downwards, Cuvier remarks, that a lamina of their parietal, their posdescending more than the articular facet for the lower jaw, terior frontal, their mastoidean, their temporal, and their and leaving between it and the elevated part of the ex-jugal, unite together, and with the tympanic cavity by ternal border a wide notch. Between this angle and the sutures, to cover the whole region of the temple with a articular facet is a fossa, hollowed in the tympanal, in the bony roof, which has no solution of continuity. Their sphenoïd, and the pterygoïdean bones. The mastoïdean muzzle being shorter than in other tortoises, and their or tubercles are depressed, very much projecting backwards, bits much longer. their nasal cavity is smaller, and as wide and pointed; their point is formed by the mastoïdean and as it is high and long. Its posterior wall belongs entirely to the external occipital. On each side in front of the tym- the anterior frontals, and it is between them that the olfac panic cavity the lower border of the skull has a wide notch tory nerves are introduced. The bony tubes of the back cut in the temporal, the jugal, and the lower maxillary, nostrils commence in the lower part of this posterior paras in the Land Tortoises. The sphenoid shows itself below tition, and, like the palatines, have a palatine part or lower on a surface much wider than in the Land Tortoises, and lamina; these tubes are rather longer, more directed backthe basilary appears less. The lateral occipitals are also wards, and bear less resemblance to simple holes. It revery small, and are promptly anchylosed with the basilary sults also from the size of the orbit that the inter-orbita! bone. The tubercle for the articulation with the atlas is membranous or cartilaginous space is more extended. less projecting than the mastoïdean apophyses. In the The portion which Cuvier regards as the temporal ala is, Testudo (Emysaura*) serpentina, Cuvier no longer found he observes, singularly small in Chelone Mydas, entirely at a certain age the external occipital distinct. It was at the external surface, and simply resting on the suture united to the lateral occipital; whilst in the Land Tor- of the descending part of the parietal and pterygoidear toises it is to the upper occipital that it is, rather, united. bones. In Chelone Caretta and Chelone Caquana Cuvie: The skull of the Testudo serpentina is, he observes, de- could not find even a vestige of it. The ossiculum auditus pressed anteriorly, the muzzle very short; the orbits does not pass by means of a hole, but of a large notch. moderate and approaching the muzzle; the temple covered from the first chamber of the tympanum into the second, only at its anterior part by a lamina of the parietal bone, and this second is cartilaginous throughout its posterior less complete than in the turtles, and by an enlargement partition; it is by the same notch that the Eustachian of the posterior frontal and of the jugal bones. The tube descends towards the back of the mouth. The firs palatines have no palatine lamina; the palatine and chamber of the tympanum is slightly concave; there is pterygoïdean region is very flat. The analogous holes of no mastoidean cellule so called; but the mastoidean bone the pterygo-palatines are very large. The passage of the completes only the ceiling of this chamber, and thus exOssiculum auditûs is made by a hole, and not by a fissure. tends its cavity. The hole of the fifth pair is oval and In the Trionyces, or Soft Tortoises, the skull, Cuvier ob- very large between the descending portion of the parieta). serves, is depressed, and elongated backwards; the muzzle, the pterygoïdean, and the petrous bone; for the rest, the pointed in certain species (that of the Nile, for instance), skull of the species of Chelone resembles that of the preis short and rounded in some others. The intermaxillary ceding tortoises. Cuvier believed that he had discovered bones are very small, and have neither nasal nor palatine in one of the species (a young Chelone Mydas) a vestige apophysis; there is behind them a large incisive hole. of a suture that might separate a lachrymal bone from the The maxillaries unite upon the palate for a rather long orbital part of the maxillary bone: it was however only an space, so that the posterior nostrils are more backward indication scarcely so strong as that which marks the interthan in the Land Tortoises. The palatines do not unite maxillary of man. below to prolong the palate; they are hollowed into a demi-canal anteriorly, and less extended than in the Land Tortoises. The body of the sphenoid reaches up to them, passing between two pterygoidean bones, which do not unite, but extend from the lateral occipital, between the tympanic cavities and the basilary bone, and to the sides of the body of the sphenoïd to the palatines and maxillaries, a conformation which renders the whole of the basilary and palatine regions wide and flat. Above, the anterior frontals advance between the maxillaries and supply exactly by this part the place of the proper bones of the nose without any distinguishing suture; they even proceed to form a point on the external aperture of the nostrils, as the bones of the nose often do in the mammals. The principal frontals form nearly a square; they reach the border of the orbit. The jugal forms a part of the posterior and lower border of the orbit, and nearly the whole of the zygomatic arch, of which the squamous portion of the temporal bone forms only a small part in front Chelydra serpentina, Schweigg, &c., Chelonura and Emys of other authors. But, Cuvier observes, the most heteroclite skull among the tortoises is that of the Matamata (Testudo fimbriata). Extraordinarily large and flat, it seems, as he remarks, to have been crushed. The very small orbits are close to the end of the muzzle. The posterior region of the cranium is elevated; and the two tympanic bones, in form of trumpets, widen out on each side of the cranium. The temple is a wide horizontal fossa, not deep, and not at all covered, except behind by the union of the posterior angle of the parietal with the mastoïdean bone; and, what is peculiar, Cuvier observes, to this subgenus, this fossa is not framed in externally, because there is no temporal bone, or, at least, it is reduced to a simple vestige. The two maxillaries form together a transversal arch, in the middle of which, below, is a single intermaxillary, and, above, the external aperture of the nostrils, which is continued into a small fleshy proboscis. The two palatine bones, and, between them, the vomer, fill below the concavity of this arch, and have in front the two back nostrils well separated, but which the palatines do not encircle below. At the posterior border of the palatine is a rather large pterygopalatine hole. The anterior and posterior frontals form the upper part of the orbits. The principal frontals advance between the anterior frontals to the edge of the external nostrils. There is no more nasal bone than in the other tortoises. The jugal proceeds from the posterior angle of the orbit between the maxillary and posterior frontal, beyond which it does not go, touching a little behind and below the pterygoidean; but not forming any projection behind to border the temple. This last is in this manner separated from the orbit by a postorbital branch of excessive width, and which takes in the totality of the posterior frontal and the jugal bones. The posterior frontal articulates itself to the pterygoïdean by its external posterior angle. The rest of its posterior border is free, and is continued with that of the parietal to cover a wide and flat canal of communication, proceeding from the temple to the orbit, and formed below by the pterygoïdean and palatine bones. The two pterygoideans are enormous. They form the greatest part of the base of the cranium and of the bottom of the temple. Their external border is curved in its anterior part for its continuation with the free border of the posterior frontal: there are neither orbital nor temporal alæ. The parietal bones, which form above a great rectangle, unite by their descending portions to the palatines, the pterygoideans, the petrous, and the upper occipital bones. They form by themselves nearly the whole roof of the cranium. Following the pterygoïdean, the temple is bounded behind by the tympanic bone or the tympanic cavity, which resembles in part, a trumpet. The frame of the tympanum is complete. A hole in the posterior wall suffers the ossiculum to pass into the second chamber, which, in the skull, is only a long groove of the posterior surface of the cavity, which terminates in a hollow, in the formation of which the petrous bone, the external occipital, and the lateral occipital concur. It is not closed behind, except by cartilage and membranes; and in the wall of the side of the cranium are pierced the two fenestræ, as ordinarily. Above this hole of the first chamber, by which the ossiculum passes, is another which conducts into the mastoïdean cellule, which, on account of the outward projection of the tympanum, is found within and not behind. The occipital spine is a short vertebral crest, and the mastoïdean tubercles are transversal crests, which belong entirely to the mastoïdean. Even in large individuals the six occipitals ordinary to the tortoises may be distinguished. Below, the smooth and nearly plane cranium presents a sort of regular compartment, formed of the intermaxillaries, the maxillaries, the vomer, the palatines, the pterygoïdeans, the sphenoid, the petrous bones, the tympanic cavities, the basilary, and the lateral and external occipitals. Behind the ceiling of the temple the petrous bone forms a square compartment between the pterygoïdean, the tympanic cavity, the external occipital, the superior occipital, and the parietal bones. The lower jaw of the tortoises is divided in a manner which it is not very easy to refer to that manifested in the crocodile, to which, Cuvier observes, that of the birds has a much more striking relation; but the bird's jaw, he adds, also approaching to that of the tortoises, aids us in referring it to a common type. The space occupied in the crocodile by the two dental and the two opercular bones is filled in the marine tortoises, the fresh-water and land-tortoises, as well as in the Trionyces, with a single bone only, the analogue of the two dental bones. Cuvier never saw in all these subgenera, even in their youth, any trace of symphysis: the bone is continuous in the tortoises, as in birds. The Matamata, or Chelys, on the contrary, preserves in every age a division at the anterior part. The opercular bone always exists, as in the crocodile, at the internal surface; but it is carried farther backward, and attains to the posterior extremity. Beneath it is the angular bone forming the lower edge of the jaw. That which Cuvier names the surangular bone occupies the external surface of this part of the jaw, and proceeds also to its posterior extremity, but only touches the angular bone quite behind, and in becoming separated on the two anterior thirds by a long point of the dental bone. Above, and towards the back part, between the opercular and surangular bones, the articular bone is situated, as in the birds; but in the tortoises it is reduced to smaller dimensions, only serving for the articulation and for the insertion of the depressor muscle, or the analogue of the digastric muscle. The co Cuvier saw in the Emys expansa the surangular, the opercular, and the articular bones anchylosed, and their sutures effaced, at a period when all the others were still visible. The general form of the bony jaw corresponds nearly to what is seen externally. More pointed in the Trionyces and Chelone Caretta; more obtuse, more parabolic, in Cheone Mydas and the land-tortoises; semicircular in front of the coronoïd apophyses in the Matamata; it differs also in the furrow with which it is hollowed: this furrow is narrow, deep, and equally wide in the land-tortoises; widens and deepens towards the symphysis in Chelone Mydus; and is entirely wanting in Trionyx, Chelone Caretta, &c. of the bone is in the form of an oblong buckler, concave above for the support of the larynx and the commencement of the trachea, and drawn out in front into a point which penetrates into the flesh of the tongue in passing upon the lingual bone. It presents on each side an angle for carrying the anterior horn, which is very small; the great horn curved into an obtuse angle for going round the œsophagus and jaw, more bony than all the rest of the apparatus, is articulated to the middle of the lateral border of the body of the bone, and its free or upper extremity is terminated by a small cartilaginous articulation. The posterior horns are articulated to the posterior angles. They are cartilaginous, flat, rather wide, and scarcely arched. The os hyoides of the tortoises is more complicated than Bones of the trunk: dorsal buckler, or Carapace.-The that of the crocodiles, and varies singularly in form from wide differences prevalent in the modification and arrangeone genus, and even one species to another. It is in gene- ment in the bones of the head in this order lead one to ral composed of a body itself, sometimes subdivided into expect, as the great French zoologist observes, proportional many pieces, and of two, sometimes three pairs of horns; differences in the rest of the skeleton. The cranial differand under the anterior part of its body is, besides, sus- ences are, as he remarks, greater perhaps than obtain pended a bone or a cartilage, sometimes double, which is among the whole of the mammals, and most certainly are the true bone of the tongue analogous to that seen in the more extensive than can be found in the whole class of birds, but articulated in them in front of the body of the birds. os hyoïdes, whilst in the tortoises it is suspended below it. The greatest horns (the anterior pair when there are only two, the middle, when there are three, representing the styloïdean bones) embrace the esophagus, and mount behind the muscles which are the analogues of the digastrics, or depressors of the lower jaw, but without being fixed otherwise than by their proper muscles. The landtortoises have the body of the os hyoïdes wider, its anterior portion longer, and want the small anterior horns, whilst the anterior angle is very much developed. In the middle of the disk are two round spaces, which in certain tortoises, the T. Indica for example, are only more delicate; but which in the others, Testudo radiata for instance, are absolutely membranous. In some fresh-water tortoises, Testudines Europea and clausa for example, the body of the bone is longer than it is wide; and has in the front a small membranous space, and at its anterior angles the small lateral horns. Sometimes two or even four osseous nuclei are there formed. The os hyoïdes of Trionyx differs still more. Its body is composed in front of a cartilaginous point, under which is suspended a great lingual oval cartilage. At the base of this a rhomboïdal osseous piece adheres on each side, which piece represents the anterior horns, and afterwards four others forming a thick disk, concave above, wider in front, and notched on the sides and behind. At the anterior angles of this disk adhere the middle horns, and to the posterior angles are attached the posterior horns: all four are very bony. The middle are formed by a long piece, which is compressed, arched, and terminated by a small cartilage. The others are wider, flatter, and prolonged by a cartilage, in the substance of which are encrusted in a row from five to six bony nuclei, which are round or oval, very hard and very distinct; so that the entire bone comprehends twenty different osseous pieces, which appear to remain distinct to old age. The general distinguishing character of the tortoises, that which separates them from all the Vertebrata, is the external position of the bones of the thorax, enveloping with a cuirass or double buckler the muscular portion of the frame, and serving also as a protection for the shoulderbones and the pelvis. The dorsal buckler is principally formed of eight pairs of ribs, united towards the middle by a longitudinal succession of angular plates, which adhere to the annular parts of so many vertebræ, or even form a part of them; but it is remarkable that these annular portions alternate with the body of the vertebræ and do not correspond directly with them. The ribs are inlaid by means of sutures into these plates; they are also united with each other, on the whole or a part of their length, according to the species, and even in each species according to the ages of the individuals. There are eight anterior vertebræ which do not enter into this conjunction. The seven first (the ordinary cervical) are free in their movements. The eighth, which may be regarded as the first dorsal, is placed obliquely between the last cervical and the first of the fixed vertebræ of the dorsal buckler, which shortens it anteriorly; behind, its spinous apophysis is elongated, and enlarges a little to attach itself by synchondrosis to a tubercle of the first of the plates of the intermediate series of the plastron. The first of these fixed vertebra, which is the second dorsal, is still rather short, and carries also its proper annular part, the spinous apophysis of which, shorter than the preceding, attaches itself to the second plate by a cartilage. This second plate, narrower than the first, forms but one bone with an annular part which is below, and of which the anterior portion is articulated by two small apophyses with the articular apophyses of the second dorsal. This, properly speaking, is the annular portion of the third dorsal vertebra; but the body of this third vertebra is only articulated by its anterior moiety with the posterior moiety of this third annular part, and by its posterior moiety it is articulated to the anterior moiety of the fourth annular portion; and this alternative continues, so that the body of the fourth vertebra responds to the annular portions of the third and the fourth, the body of the fifth to the annular portions of the fourth and fifth, and so on to the tenth. The most singular of all these is that of the Chelys, and is very early entirely ossified. Its body is composed of a long, narrow, prismatic piece, hollowed above by a canal where the trachea runs. In front this piece is dilated, and carries on each side two angular portions, four in all, without counting the piece itself. The two intermediate ones unite in front, leaving between them and the principal body a membranous space on which the larynx reposes. The lateral portions, Cuvier observes, represent But it is necessary to distinguish in the ribs the plate perhaps the small anterior horns. It is on the angle included in the buckler, and a small branch which prowhich they form with the dilatation of the principal body ceeds from its lower surface, and which represents what is that the middle horns are articulated; these last are very termed the head of the bone in the ordinary ribs. This strong, prismatic on their internal moiety, and then slen-head is always articulated between two bodies of vertebræ. der, and terminated by a bony and pointed piece, distinct The first of all these ribs has only this small branch, with from the rest of the horn. The posterior horns are articu-out having any plate belonging to it in the buckler, ex lated at the posterior extremity of the prism formed by the principal body. They are long, strong, slightly compressed, and curved into an arch. Under the anterior and dilated part is suspended the true bone of the tongue, formed in front of a semicircular cartilage, and behind of two bony pieces in form of a crescent, the internal angle of which is prolonged into a sort of tail or pedicle, which lies under the prismatic body of the os hyoides. In the Turtles (Chelone Caretta for instance) the body cepting only in some of the Emydes, where may be seen, between the first and the second longitudinal plate, and the first or second widened rib, a small piece which can only represent the enlarged portion of this first rib, but which does not belong to its head. It is articulated between the eighth vertebra or first dorsal, and the first fixed vertebra, and by its other extremity applies itself to the internal surface of the second rib. This last has a plate which incorporates itself by its anterior border with the first of the longitudinal series, by its spinal border with the second piece of that series or the annular portion of the third vertebra, and by its head between the body of the second vertebra and that of the third. The succeeding ribs observe the same law, are articulated by means of their head between the body of one vertebra and that of the succeeding vertebra, and incorporate themselves by means of their dilated part with the plate which represents the annular portion of the second of these two vertebræ: and this, Cuvier observes, is a return to the general law; for in man and in the quadrupeds the ribs are articulated by their head between two vertebræ, and, by means of their tuberosity, with the transverse apophysis of the second of the two. The dilated portions of the ribs of the tortoise, in the part where they are incorporated with the plates of the longitudinal series, represent, then, the tuberosities of the ribs of mammals. The ninth plate of the longitudinal series, which belongs to the tenth dorsal, is the last with which a pair of the dilated ribs is incorporated, and this last is the ninth in all or the eighth of those which enter into the composition of the dorsal buckler. It is directed from its posterior border backwards, and embraces again the succeeding plates, with the external edges of which it becomes incorporated: but these three plates do not, any more than the first, serve to complete the vertebral canal. The tenth rib, attached between the bodies of the tenth and eleventh vertebræ, produces no plate and enters not into the composition of the dorsal buckler. Like the first, it has only a portion of the head, and is joined by its other extremity to the internal surface of the ninth. The eleventh vertebra after the cervical is the only one that can be termed lumbar; it carries no rib. In the Turtles, its annular portion again gives a plate to the longitudinal series of the dorsal buckler, and is the tenth and the smallest of the pieces of this series. The twelfth and thirteenth vertebræ are the sacral. At their sides are attached two lateral pieces sufficiently similar to the heads of the ribs, but stronger, especially the first, and convex at the end, in order to their union with the posterior and upper angle of the ossa ilii. Their annular portion is close and complete, and is not incorporated with the plates of the buckler which follow that of the eleventh vertebra. The vertebræ of the tail are free, like those of the neck: hence the plates of the longitudinal series, which follow the tenth, do not adhere to the vertebræ, and, if they belong thereto, only so belong by a metaphysical relation, and accordingly they may be considered as having been dismembered. So of the first of all the plates of the series. It only furnishes an attachment to the annular portion by synchondrosis, otherwise close and complete, of the first dorsal vertebra, and if one would regard it as belonging thereto, it would be necessary to consider it as dismembered. The Turtles have three longitudinal plates after the tenth, making thirteen in all; but the second is sometimes divided into two, and the ninth also, which increases their number to fifteen. Cuvier found fourteen in some of the Emydes, the Emys serrata for instance; but the eleventh and twelfth, he adds, are very small in them. There is but a single one after the tenth in the Land Tortoises and the Chelydes, so that they have only eleven in all. It sometimes happens that one or two of these plates are not seen externally. Thus in the Box Tortoises the two ribs of the last pair are joined to each other and thus cover the ninth plate; and in this respect many modifications occur in the same species; of which Bojanus has, in his third plate, given many examples taken from the European tortoise. In Chelys the last and penultimate rib are attached to the eighth plate, and the ninth remains hidden. In both cases the tenth and the eleventh subsist as ordinarily. In the Turtles, the eight pairs of ribs and the thirteen plates of the longitudinal series form a slightly convex oval buckler, a little narrowed backwards. The ribs are not incorporated throughout their length, a narrow fraction remains towards their exterior, and the intervals between this portion and that of the anterior and posterior ribs are filled up by a cartilaginous membrane only. It is only in extreme old age that some are widened to the end. Cuvier had sometimes seen the three first and a part of the fourth in this state. In the freshwater Tortoises and in Chelys, the buckler is entirely filled up in time, and the ribs incorporate them |