CHELONIA X€A6vs, a Tortoise), Tortoises and Turtles, a numerous and highly interesting order of Reptiles, generally con sidered the first by herpetologists. They are also termed Testudinata (from Teatudo, the Latin name for a Tortoise), and are distinguished at the first glance by the double shield in which their body is normally Inclosed, whether they are terrestrial, fresh-water, or marine. They were all comprised by Lituueus under his genus Testuclo.
The following account of the organisation of these animals is principally derived from Cuvier.
Skeleton.—The surface of the skull in these reptiles is continuous, being without any moveable articulations, as is the ease 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 Land-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 back wards. 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 fossfe, under which are enormous tympanic cavities; behind these cavities, and a little above, project two large ma.stoidean protnberances, 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 eondyle 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 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 from its congener, and especially very far behind time internal nostrils. On the palate, or rather, behind the roof of the back of the mouth, may bo seen the orifices of two tubes, under the form of two small holes separated from each other.
place in the frame of the orbit, is articulated also, as ordinarily, to I the ante-orbital apophysis of the maxillary bone, descends within the orbit, forma the anterior septum, which separates the orbit from the nose, and is articulated below with the palatine and the coiner, leasing between it, the maxillary, and the palatine, en oblong bole, which leads into the posterior nostrils. The osseous cavity of the none is oblong, and formed by the maxillaries, the intermaxillaries, the comer, the two anterior and the two principal frontal& • 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 frontala up to the posterior frontal, in Testudo Indira, or very near it in sorno other species. The intermaxillaries have no ascending apophysia. 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 corner. The posterior nostrils are two large aperture pierced on each Bide in the middle of the nasal cavity betweeu the maxillaries, the intermaxillaries, the corner, and the anterior frontal bones. The bottom of tho 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 permits the passage of the filaments of the olfactory nerve. Lower and laterally there is, between the frontal, the anterior frontal, and the comer, a rather large space closed by a continuation of the same cartilage, which represents the os plenum. In the Terrestrial
Tortoise there is no inter-orbital simple cartilaginous septum, or nearly none ; hut this is not so in other sub-genera. 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 fosse; 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. 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 Cetacen. The temporal bone widens to unite itself to the tympanic cavity, which is extremely large. It forms a frame which is nearly completely bony for a large tympanum ; and below this frame it descends in form of an apopbysis for the articulation of the lower jaw. This frame leads into a vast cavity, completed only at its upper posterior angle by the mastoidean. At the bottom of this cavity is a hole through which passes the osaieulum auditfia to arrive at a second cavity, formed externally by the bone of the tympanic cavity, on the internal Bide by the petrous bone and the occipital bones, below a little by the aphenoid bone, and closed backwards by cartilage. It is a second part of the tympanic cavity which is thus divided by a constriction, of which we have examples among the mammals, especially in the genus Fclis, but the communication between the two parts is lees narrowed than in the Tortoise. The tympanic bone forms besides a considerable part of the posterior walla of the temporal fosse. Between it and the parietal the petrol's bone shows itself in this same temporal fewer, and the cranium is defied behind by the occipital bone, which is here divided into six bones, not into four; for the lateral occipitals are each divided into two parts, the most extents' of which Cuvier terms tho exterior occipital. Tbc fenestra ovalis is, he observes, common to the patrons bone and this exterior occipital ; as, in the crocodile, it is common to the petrous bone and the ordinary lateral occipital: the fenestra rotunda, on the contrary, is pierced in the exterior occipital, as it is pierced in tho lateral occipital of the crocodile. The two bones contribute to the formation of the cell of the labyrinth with the upper occipital, as the petrous bone and the lateral occipital contri bute to it in the crocodile. In both genera the great aperture for the exit of the fifth pair of nerves is in front of the petrol's bone, between it and the temporal ala. In the Turtle this hole is between the petrous bone and the descending part of the parietal bone. The osoricolurn anditne is simple, as in the crocodile, and formed of a slender stem, which widens at the point of its approximation to the fenestre ovalis, and which Is there applied by a round and concave surface, so that it hex nearly the figure of a trumpet. The Eustachian tribe is entirely cartilaginous or membranous. It commences in the external chamber of the cavity, above, by a large notch of the posterior border of the tympanic bone, near the edge of the tympanum itself, and is directed obliquely within, parsing between the bone of the cavity and the depressor muaclo of the lower jaw, to ft notch of the lateral and posterior border of the pterygoid bone, whereby it penetrates into the back of the (amen, on the side, close to the articulation of the lower jaw, but far enough 1, Profile ; 2, seen from above; 3, seen from below; 4, seen from behind.