equilibrium and movement of elastic bodies, which is given in the Mémoires de l'Académie des Sciences' (tom. viii.), has deduced the same law from purely theoretical considerations. It may be convenient to compare the force of torsion with that of gravity, and for this purpose it will be necessary to observe merely that the time in which a pendulum, whose length is 1, makes a complete oscillation in a very small are is expressed by ☛ (-) * [PENDULUM, p. 406], force of errestrial attraction (= 24 X 35", or 840°); thus ก g The bifilar magnetometer' which was invented by M. Gauss, is a species of torsion balance: it is described briefly in the article TERRESTRIAL MAGNETISM, and at length in Taylor's Scientific Memoirs, vol. ii., part 6. The apparatus with which, by the oscillations of two balls of lead at the extremities of a lever suspended horizontally by a string, Mr. Cavendish determined the average density of the earth, was also a balance acting on the same principle. [ATTRACTION, p. 68.] extremity of each; but the poles of the same denomination in the two needles being presented to each other, a repul sion took place, and the suspended needle came to a state of rest between the opposing forces of torsion and of magnetic repulsion. When the micrometer at E was allowed to remain in its actual position, the suspended needle was repelled 24 degrees, and consequently it was prevented from returning to the zero point by a force of torsion expressed by the sum of 24 degrees, and of the horizontal the whole force of magnetic repulsion was expressed by where g represents the force of gravity: then the time in 864 degrees. In a second experiment, the wire being which the torsion wire vibrates once on its axis being twisted by making the stem at E perform three revolutions made equal to the time in which a simple pendulum (= 1080°) in a direction contrary to that of the 24 degrees vibrates, we have (using the formula in ELASTICITY), before mentioned, the needle rested at 17 degrees from KM เ therefore as the momentum of inertia for a zero: the force of magnetic repulsion was then expressed by the sum of 1097 degrees, and the value of terrestrial torsion wire suspending a body of a given form can be attraction (= 17 x 35°, or 595°); that is, in all, 1692 decomputed, and as I may be found from the observed time grees. On comparing together several experiments of the of a vibration, the value of n (the coefficient of the force same nature, and also several similar experiments in which of torsion) can be ascertained from this equation. the poles of a contrary denomination were presented to The torsion of slender wires was first employed by Cou- each other, Coulomb found, neglecting small differences lomb for the purpose of determining the intensities of which may be supposed to have arisen from the extent and forces in nature and the laws of their action in circum- configuration of the needles, that the forces of magnetic stances which render direct methods inapplicable: his ex-repulsion and attraction vary inversely as the squares of the periments were performed with an instrument which he distances. invented, and which he designated a torsion balance. In the article ELECTROMETER there is given a description of the instrument and of the method of employing it in finding the laws of electric attractions and repulsions; and it will therefore be sufficient in this place to explain its application in determining those of magnetic action. For this purpose Coulomb adapted to the suspending wire, which was of copper, a small stirrup, as W, also of copper, in which could be placed a magnetized needle of steel. Before this was done however, a copper needle, equal in weight to the magnetized needle which was to be used in the experiment, was placed in the stirrup, and the plate Dat the top of the glass case was turned round till one extremity of the copper needle, which turned with the plate, was brought to the zero of the graduations on the horizontal circle bac in the case, the suspending wire being in an untwisted state: the whole case was afterwards turned round till the needle, still pointing to zero, was in the direction of the magnetic meridian, which had been previously determined. The copper needle was then taken away, and the magnetized needle put in the stirrup; and as soon as it was at rest in the magnetic meridian, the suspending wire was twisted by turning the stem E, to which it is attached at the upper extremity of the case, fill the index there had passed over some given number of degrees, which in one experiment was 360. The suspended needle was thus made to deviate from its previous position 10 degrees, in which state the horizontal force of terrestrial magnetism was in equilibrio with the force of forsion; and the angle of torsion was then equal to 3494° (=360°-104°). On turning the index at E through two revolutions, the needle was observed to rest between the opposing forces, at 211° from its original place, when consequently the angle of torsion was 698° (= 720°-214°). Obtaining in like manner several other angles of torsion with the corresponding deviations of the magnetic needle, and comparing them together, Coulomb found that the forces of torsion are constantly proportional to the sines of the deviations of the needle. In order to discover the law of magnetic action with respect to the distances between the attracting or repelling bodies, Coulomb placed a magnetized needle in the stirrup of the balance, and after twisting the wire by turning the micrometer stem at E on its axis through a certain number of degrees, he observed where the needle rested between the opposing forces of torsion and the horizontal compoBent of terrestrial magnetism: assuming then that the devations of the needle were proportional to the forces of torsion, he found that, in order to make the needle deviate one degree, it was necessary to employ a force of torsion expressed by 35 degrees. The wire being then untwisted, and the magnetized needle placed in the magnetic meridian, Coulomb introduced in the glass case, in a vertical position, and also in the plane of the magnetic meridian, a magnetized needle of the same dimensions as the other, so that if the two needles could have approached each other they would have been in contact at about an inch from the For the strain of torsion in machinery, see MATERIALS, STRENGTH OF. TORTENSON. [THIRTY YEARS' WAR.] TORTI, FRANCIS, an eminent Italian physician, w23 born at Modena, December 1st, 1658. Having finished his preliminary studies in 1675, he was originally intended for the legal profession; this however he soon abandoned, and embraced that of medicine, which he studied under Antonio Frassoni. He took the degree of Doctor of Medicine at Bologna in 1678, and upon his return to Modena, at the early age of twenty-three, he obtained one of the medical professorships founded by the duke Francis II. Soon afterwards he was chosen to be one of the physicians in ordinary to the duke, an appointment which he owed partly to his accomplishments in music and literature, as he was the composer of several oratorios, and also wrote a Latin letter under the assumed name of L. A. Cotta, in defence of Tasso against Bouhours. Upon the death of Francis in 1694, his successor continued Torti in his place of physician in ordinary; he was also prevailed upon by his representations to found an anatomical amphitheatre at Modena, in which Torti was entrusted with the office of demonstrator in 1698. He had previously joined with Ramazzini in carrying on some researches concerning the barometer, the results of which were published by the latter under the title Ephemerides Barometricae Mutinenses,' Modena, 1694; and again Dissertatio altera Triceps circà Mercurii Motiones in Barometro,' Modena, 1698. But Torti's most important and celebrated work did not appear till 1709, under the title Therapeutice Specialis ad Febres quasdam Perniciosas, inopinato ac repente Lethales, una verò China China Peculiari Methodo ministrata,' Modena, 8vo. This work placed him at once in the first rank among practical physicians, and still continues to be highly esteemed. It has been several times reprinted, the last edition (of which the writer is aware) being published at Paris, 1821, 8vo., in 2 vols. publication of this work gained him the friendship and applause of various learned men, and also the title of corresponding member of the Royal Society of London, and of the Academy of Valentia in Spain. It also drew forth some criticisms from Manget and Ramazzini, to whose remarks he replied with some degree of bitterness and warmth. In 1717 he was offered the professorship of Practical Medicine at Turin, and in 1720 he had a similar offer at Padua, but he refused them both, and preferred living at Modena, where he had honours and emoluments heaped upon him by the duke. An incurable trem The bling of the hands having rendered him unable to feel the pulse of his patients with sufficient accuracy, he gave up practice some years before his death, and passed the remainder of his life in honourable repose, often consulted by patients from all parts, and spending much of his leisure time in the pleasures of the chase, to which he had always been much addicted. Having been summoned by the prince of Parma, in 1731, to attend Henrietta d'Este, he was, upon his return to Modena, seized while in a church with a sudden attack of hemiplegia, brought on probably by heat and over-exertion. For some time after-mits the passage of the filaments of the olfactory nerve. wards he lost the use of his right side, but gradually recovered, and lived for ten years after the attack. He latterly became dropsical, and died in March, 1741, at the age of eighty-two. He was twice married, but having no children, he left part of his fortune to found another medical professorship at Modena, and directed the rest to be given away in charity. (Biographie Médicale.) TORTOISES (Testudinata), a numerous and highly interesting order of REPTILES, generally considered the first by herpetologists. They are also termed Chelonians, from XEλvn (chelone), the Greek name for a tortoise, and are distinguished at the first glance by the double shield in which their body is normally enclosed, whether they are terrestrial, fresh-water, or marine: they were all comprised by Linnæus under his genus Testudo. ORGANIZATION. Skeleton. The surface of the skull in these reptiles is continuous, being without any moveable articulations, as is the case with the serpents and the Tailed Batrachians. But whilst this character prevails in all the genera of which the order is composed, many of those genera differ much in their cranial structure, and it becomes necessary to point out these differences, which are much greater than those which exist in the crania of the Crocodiles. In the Terrestrial Tortoises the head is oval and obtuse anteriorly; the interval between the eyes is large and convex; the aperture of the nostrils is large, higher than it is wide, and a little depressed backwards. The orbits, which are large, are nearly round, complete throughout, directed sideways, and a little forwards. The parietal region terminates backwards in a large projecting occipital spine, and has on each side two large temporal fossæ, under which are enormous tympanic cavities; behind these cavities, and a little above, project two large mastoidean protuberances, and beneath them are the apophyses, which serve for the articulation of the under jaw. These apophyses descend vertically, and are not directed backwards, as in the Crocodiles. Underneath, the basilary region is flat, the palatine concave; and upon the anterior part of this last the osseous posterior nostrils open, there being no palatine roof, and the palatine part of the maxillaries being open up to the anterior fourth of the muzzle; a disposition rendered necessary by the mode of respiration in these animals, and which as much resembles that of the Frogs as it differs from that of the Crocodiles. The occipital region is in its totality vertical, although the occipital spine, the mastoidean protuberances, and the articular condyle of the skull, which is a very projecting tubercle, render it very unequal. The first remarkable feature in the composition of the head of the Tortoises, remarks Cuvier, from whose observations the osteology of the order is principally taken, is the absence of nasal bones. In the recent animal the external bony nostrils are narrowed by cartilaginous lamina, which represent these bones; but in the skeleton is found immediately at their upper border the anterior frontal bone, which takes its ordinary place in the frame of the orbit, is articulated also, as ordinarily, to the ante-orbital apophysis of the maxillary bone, descends within the orbit, forms the anterior septum, which separates the orbit from the nose, and is articulated below with the palatine and the vomer, leaving between it, the maxillary, and the palatine an oblong hole, which leads into the posterior nostrils. The osseous cavity of the nose is oblong, and formed by the maxillaries, the intermaxillaries, the vomer, the two anterior and the two principal frontals. The extent of the anterior frontals and the absence of the nasal bones are the causes that the first articulate with each other, and that they extend above the orbit and outside the principal frontals up to the posterior frontals in Testudo Indica, or very near it in some other species. The intermaxillaries have no ascending apophysis. They form, as ordinarily the termination of the muzzle, and are directed backwards in the palate between the maxillaries, and even between the posterior nostrils, to the vomer. The posterior nostrils are two large apertures pierced on each side in the middle of the nasal cavity between the maxillaries, the intermaxillaries, the vomer, and the anterior frontal bones. The bottom of the cavity of the nose is covered above and closed behind by the principal frontals, which leave a large aperture between them closed by a cartilage which perLower and laterally there is, between the frontal, the anterior frontal, and the vomer, a rather large space closed by a continuation of the same cartilage, which represents the os planum. In the terrestrial tortoise there is no interorbital simple cartilaginous septum, or nearly none; but this is not so in other subgenera. The frontals cover but very little of the cerebral chamber, because they are short, and together form a lozenge wider than it is long. The parietals form together a pentagon, the most acute angle of which proceeds to unite itself with the occipital spine. They cover more than half of the cerebral chamber, and are directed backwards by means of a scaly suture on the occipital bone and on the petrous bone. On each side the parietal bone descends very low into the temporal fossa: there it occupies nearly all the space which the temporal wing of the sphenoid bone occupies in the crocodile, and in the tortoise there only remains a very small portion of this bone, which unites on one side to the descending portion of the parietal; on the other to the palatine, the internal pterygoid, the body of the sphenoid, the tympanic cavity, and the os petrosum. In the Chelone Mydas (tortue franche) it is still smaller, and joined to the descending foot of the descending portion of the parietal bone. The jugal bone is articulated, as ordinarily, with the external and posterior angle of the maxillary bone. It is narrow and continued under the orbit, behind which it encounters the posterior frontal bone, which completes the frame in this part, and the squamous portion of the temporal bone, which forms by itself the whole zygomatic arch, as may be seen in many of the Cetacea. The temporal bone widens to unite itsel to the tympanic cavity, which is extremely large. It forms a frame which is nearly completely bony for a large tym panum; and below this frame it descends in form of ar apophysis for the articulation of the lower jaw. This fram leads into a vast cavity, completed only at its upper poste rior angle by the mastoidean. At the bottom of this cavity is a hole through which passes the ossiculum auditus t arrive at a second cavity, formed externally by the bone o the tympanic cavity, on the internal side by the petrou bone and the occipital bones, below a little by the sphenoi bone, and closed backwards by cartilage. It is a secon part of the tympanic cavity which is thus divided by constriction, of which we have examples among the mam mals, especially in the genus Felis, but the communication between the two parts is less narrowed than in the tortoise The tympanic bone forms besides a considerable part o the posterior walls of the temporal fossa. Between it an the parietal the petrous bone shows itself in this sam temporal fossa, and the cranium is closed behind by th occipital bone, which is here divided into six,-not int four bones; for the lateral occipitals are each divided int two parts, the most external of which Cuvier terms th exterior occipital. The fenestra ovalis is, he observe common to the petrous bone and this exterior occipital as, in the crocodile, it is common to the petrous bone an the ordinary lateral occipital: the fenestra rotunda, on th contrary, is pierced in the exterior occipital, as it is pierce in the lateral occipital of the crocodile. The two bone contribute to the formation of the cell of the labyrint with the upper occipital, as the petrous bone and the lat ral occipital contribute to it in the crocodile. In bot genera the great aperture for the exit of the fifth pair nerves is in front of the petrous bone, between it and th temporal ala. In the Turtle this hole is between th petrous bone and the descending part of the parietal bon The ossiculum auditûs is simple, as in the crocodile, an formed of a slender stem which widens at the point of i approximation to the fenestra ovalis, and which is the applied by a round and concave surface, so that it h nearly the figure of a trumpet. The external end of th stem, placed in the external part of the cavity, is, in gre t b 1, profile; 2, seen from above; 3, seen from below; 4, seen from behind. In the Emydes, or ordinary fresh-water tortoises, the same author remarks that the head is more flattened. The principal frontals, although they are wider than they are long, do not always reach to the border of the orbit, as is, for example, the case in the Testudo (Cistudo) Europea; the posterior frontal is wider. The frame of the tympanum is not complete, and in lieu of a hole there is a fissure for the passage of the ossiculum auditûs from one hollow of the cavity to the other. The basilary and palatine regions form but one plane; the palatines not being even concave. Cuvier observes that Testudines scripta, picta, scabra, dorsata, centrata, clausa, and virgulata, belong to this category. Certain Emydes, he remarks, Emys expansa for instance, tend to the Sea-tortoises or Turtles and the fresh-water tortoises, and yet exhibit characters peculiar to themselves. The head is depressed, the muzzle short, and the orbits small and placed very forward. It VOL. XXV.-I wants the bony vomer, so that its two back nostrils form | of the tympanic cavity; this last has its frame complete. but one aperture in the skull. Its palatines want the The ossiculum passes by means of a hole to enter the palatine portion. The frame of the first chamber of its second chamber of the cavity, which, as in the other tortympanic cavity is complete; this chamber communicates toises, is closed behind by a cartilage only. The Eustaonly by one narrow hole with the mastoïdean cellule, and chian tube commences by a notch of the posterior border, the Eustachian tube takes its origin there by means of a as in the Land Tortoises. The spine of the occiput and slit, which is an extension of the hole by which the ossi- the mastoïdean tuberosities are all three pointed, and proculum passes into the second chamber. The temporal ject more backwards than the articular condyle. The bone is covered, as in the turtles, by the parietal, temporal, space occupied by the tympanic cavity at the posterior jugal, and posterior frontal bones. This last is very narrow; border of the temporal fossa is very narrow, but it widens it has one portion descending into the temple, which, in descending again towards its apophysis for the lower uniting to an ascending part of the palatine bone and to jaw. The temporal ala is placed below and in front of a re-entering portion of the jugal bone, forms a partition the great hole of the fifth pair of nerves, and the descend which separates the orbit from the temporal fossa, not leav- ing part of the parietal bone articulates itself in front of i ing any communication except one great hole near that to the internal pterygoïdean. It therefore enters more int descending part of the temporal bone which replaces the the composition of the cranium, and is more easily recog temporal ala. The pterygoid unites itself forward with nised, than in the other tortoises. 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 it der is re-curved with the neighbouring portion of the jugal | place, and closes on each side the front of the cerebra 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 Tur of 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 pos descending more than the articular facet for the lower jaw, terior frontal, their mastoïdean, their temporal, and thei 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 articular facet is a fossa, hollowed in the tympanal, in the bony roof, which has no solution of continuity. Thei 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 wid and pointed; their point is formed by the mastoïdean and as it is high and long. Its posterior wall belongs entirely t 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 bac cut in the temporal, the jugal, and the lower maxillary, nostrils commence in the lower part of this posterior par as in the Land Tortoises. The sphenoid shows itself below tition, and, like the palatines, have a palatine part or lowe on a surface much wider than in the Land Tortoises, and lamina; these tubes are rather longer, more directed back the basilary appears less. The lateral occipitals are also wards, and bear less resemblance to simple holes. It r very 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 i Testudo (Emysaura*) serpentina, Cuvier no longer found he observes, singularly small in Chelone Mydas, entirel at a certain age the external occipital distinct. It was at the external surface, and simply resting on the sutur united to the lateral occipital; whilst in the Land Tor- of the descending part of the parietal and pterygoidea toises it is to the upper occipital that it is, rather, united. bones. In Chelone Caretta and Chelone Caouana Cuvi The skull of the Testudo serpentina is, he observes, de- could not find even a vestige of it. The ossiculum auditi pressed anteriorly, the muzzle very short; the orbits does not pass by means of a hole, but of a large note moderate and approaching the muzzle; the temple covered from the first chamber of the tympanum into the secon only at its anterior part by a lamina of the parietal bone, and this second is cartilaginous throughout its posten less complete than in the turtles, and by an enlargement partition; it is by the same notch that the Eustachia of the posterior frontal and of the jugal bones. The tube descends towards the back of the mouth. The fi palatines have no palatine lamina; the palatine and chamber of the tympanum is slightly concave; there pterygoïdean region is very flat. The analogous holes of no mastoidean cellule so called: but the mastoïdean bo the pterygo-palatines are very large. The passage of the completes only the ceiling of this chamber, and thus e Ossiculum auditûs is made by a hole, and not by a fissure. tends its cavity. The hole of the fifth pair is oval a In the Trionyces, or Soft Tortoises, the skull, Cuvier ob- very large between the descending portion of the pariet serves, is depressed, and elongated backwards; the muzzle, the pterygoïdean, and the petrous bone; for the rest, t pointed in certain species (that of the Nile, for instance), skull of the species of Chelone resembles that of the pr is short and rounded in some others. The intermaxillary ceding tortoises. Cuvier believed that he had discover bones are very small, and have neither nasal nor palatine in one of the species (a young Chelone Mydas) a vesti apophysis; there is behind them a large incisive hole. of a suture that might separate a lachrymal bone from t The maxillaries unite upon the palate for a rather long orbital part of the maxillary bone: it was however only space, so that the posterior nostrils are more backward indication scarcely so strong as that which marks the int than 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 sphenoïd reaches up to them, passing between two pterygoïdean 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., Chelonera and Emys of other authors. But, Cuvier observes, the most heteroclite skull amo the tortoises is that of the Matamata (Testudo fimbriat Extraordinarily large and flat, it seems, as he remarks, have been crushed. The very small orbits are close to t end of the muzzle. The posterior region of the craniu is elevated; and the two tympanic bones, in form trumpets, widen out on each side of the cranium. T temple is a wide horizontal fossa, not deep, and not at covered, except behind by the union of the posterior and of the parietal with the mastoïdean bone; and, what peculiar, Cuvier observes, to this subgenus, this fossa is framed in externally, because there is no temporal bo or, at least, it is reduced to a simple vestige. The t maxillaries form together a transversal arch, in the mid of which, below, is a single intermaxillary, and, above, external aperture of the nostrils, which is continued in a small fleshy proboscis. The two palatine bones, a between them, the vomer, fill below the concavity of t arch, and have in front the two back nostrils well separat but which the palatines do not encircle below. At 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 pterygoïdean; 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 pterygoïdeans 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 pterygoïdeans, 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 mastoidean 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 exterloccipitals. Behind the ceiling of the temple the petrous bone forms a square compartment between the pterygoidean, 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 ocodile, to which, Cuvier observes, that of the birds has much more striking relation; but the bird's jaw, he adds, o approaching to that of the tortoises, aids us in referring to a common type. The space occupied in the crocole by the two dental and the two opercular bones is filled the marine tortoises, the fresh-water and land-tortoises, well as in the Trionyces, with a single bone only, the alogue of the two dental bones. Cuvier never saw in all these subgenera, even in their youth, any trace of symis: 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 be always exists, as in the crocodile, at the internal sure; but it is carried farther backward, and attains to the sterior extremity. Beneath it is the angular bone formthe lower edge of the jaw. That which Cuvier names arangular bone occupies the external surface of this t of the jaw, and proceeds also to its posterior extremity, only touches the angular bone quite behind, and in coming separated on the two anterior thirds by a long t of the dental bone. Above, and towards the back between the opercular and surangular bones, the arular bone is situated, as in the birds; but in the torses it is reduced to smaller dimensions, only serving for the articulation and for the insertion of the depressor sele, or the analogue of the digastric muscle. The co 1, seen from above; 2, seen from below; 3, profile; 4, seen from behind. ronoid apophysis does not belong at all to the surangular bone in this order, but to a bone placed between the dental, the opercular, and the surangular bones; and in front of the aperture by which the nerves enter the jaw, an opening, which is here found at the upper border, instead of being, as in the crocodile and the birds, at the internal surface. This bone, which is not found in the birds, can only respond to the complementary bone in the crocodile. |