fllKI.ONIA. 



CHE I 



states that there were only 18 ia the Frcsh-WaU-r ami Marine 

 Tortoises which be examined. 



Sternum of Trfonyr. 



. ii urn of Culaito. 



Bones of the Extremities. The bone which goes from the dorsal 

 buckler to the sternum is suspended by a ligament under the dilata- 

 tion of the second rib, but in front of the first, which, as we hare seen, 

 consist* only of a head articulated under the second ; so that in some 

 respects this bone is outside the thorax. There is sometimes in tin- 

 ligament by which it is attached one, and even two, peculiar bones. 

 This bone is at first nearly cylindrical : it proceeds forwards, ami 

 after bavin!; afforded on its external surface a portion of the articular 

 facet which receives the bead of the humerus, it goes with a more 

 or less strong inward bend to attach its other extremity to the internal 

 mil-face of the sternum, towards the lateral angle of the odd piece. 

 The rest of the facet for the articulation of the humerus is furnished 

 by another bone, which is directed more or leas obliquely backwards 

 and towards the mesial line, widening into a fan-shape, and which 

 thus lies nearly parallel to Uie sternum. The osseous branch which 

 come* from the bony buckler, is, according to Cuvier's self-corrected 

 opinion, the shoulder-blade, and the part which it offers beyond the 

 articular fosset is iU acromion. The flattened bone which is d. i 

 backwards is, he adds, iucontestably the coracoid bone : and he 

 further remarks that all the muscles which proceed from these bones 

 to go to the arm are respectively the same as in birds, whatever 

 changes they have undergone in their position relatively to the 

 horizon in their size and in their figure. Cuvier considers that it 

 nmaios to be known whether there is a clavicle or not. 



The three-branched shoulder, the nearly cylindrical shoulder-blade, 

 the acrumial portion nearly equal in volume to the rest of the 

 shoulder blade, are characteristic of the Tortoises. There is nothing 

 parallel to this conformation in the other animals, because there is 

 no other shoulder nit Mated within the thorax. The varied forms of 



these parts afford, Cuvier observes, very good characters for the sub- 

 genera ; and he details the modifications characteristic of the Marine 

 Tortoises, the Land-Tortoises, the Freeh-Water Tortoises, C'Ac/y*. and 

 Tnanyx. 



The humerus of the Tortoises is required to turn singularly upon 

 its axis, in order to place the fore foot in the position required by the 

 bony cuirass, which only leaves a narrow passage for it. Ti..< remit 

 is that its internal tuburosity is become posterior and superior, and 

 that the external tuberosity is become internal and also p- 

 The head of the bone goes out of the axis more than in am 

 animal, and that towards the posterior face which in the ordinary 

 position is the superior one. It presents the segment of a sphere, 

 and is very convex. The two tuberosities are very large, v, TV pro- 

 jecting, and leave between a concavity, as there is one backward*, 

 between the condylee of the humerus in the greater part of t)i 

 mammals. The internal tuberosity become, as has been piutl 

 out, posterior is the largest. It has the form of a long obtuse crest, 

 analogous to the deltoidean, and which receives the same muscles. 

 The other tuberosity forma a crest also, but much shorter. I'-.th 

 are near the head. The body of the bone is bent; and its coin 

 which in man would be anterior, ia ordinarily found inferior. The 

 opposed surface is convex. Above it in a small hollow opposite the 

 end of the fossa, which is between the two tuberosities. The lower 

 part of the bone is widened and a little flattened from before back- 

 wards. On the external border is a furrow, not much developed in 

 the Land-Tortoises; deeper in the Emgdct, the CMyda, and the 

 Trionyca; and which in the Marine Tortoises nearly separut 

 lower head of the bone into two unequal parts. This furrow, < 

 observes, is perhaps the best character for distinguishing the h>\\er 

 part of the humerus from that of the femur, which is without it, but 

 which in every other point offers only very slight differences. Its 

 lower head, transversely oblong and of uniform convexity, n 

 the bones of the fore-arm, but without offering two distinct facets. 



The Trionyce* do not differ from the Land-Tortoises, excepting in 

 having the tuberosities more apart. Other differences arc man 

 in Emyt and Clitlys, for which we refer to Cuvier's work, but the 

 humerus of the Marine Tortoises cannot be passed by without par- 

 ticular notice, for it differs from that of all the other Tolii'limi'-i in 

 being not bent longitudinally, but nearly straight; in luu 

 great tuberosity (the analogue of the small or internal tuberosity in 

 man) longer, overreaching the head, and resembling an olecntinui ; 

 and, lastly, in having the other tuberosity shorter, and representing a 

 chevron-shaped crest. 



There are always two bones in the fore-arm, but they have little 

 motion one on the other. They are placed, when the animal pro- 

 gresses, so that the ulna forms the external and the radius the 

 internal border of the arm. 



The radius has a semicircular, slightly concave, upper h. 

 somewhat slender body, and the lower head compressed and cut, as 

 it were, obliquely, so that it is shorter on the ulnar side. 



The ulna is compressed. Its up]>er head is triangular and cut 

 obliquely, so that its external border ia longer upwards than the 

 radial border without having a true olecranon. This border i> tren- 

 chant. The lower one is cut square. Differences occur, as in T, 

 and the Chtlonet, or Marine Tortoises. 



The pelvis is always composed of three distinct bones, contributing, 

 aa in the Mammalia, to the composition of the cotyloid fossa, n:n 

 an elongated os ilium, which attaches itself by ligaments to the 

 transversal processes of the sacral vertebra and the neighbouring 

 part of the eighth pair of the dilated ribs ; a pubis and an ischium, 

 which are directed, widening as they proceed towards the plastron, 

 and are each united to its similar piece. At the point of uni< 

 the formation of the cotyloid cavitx has tin ee faces; one 



for each of the two others and one for tb.3 cavity. On the rest of the 

 length the os ilii ia oblong, the ischium proee. d, widening as it goes, 

 directly towards the symphysis, and the pubis, after tit dn 

 itself forward, makes a curve towards the symphysis, and v 

 also to reach it. Various differences occur in this part of the skeleton 

 in the Land and Marine Tortoises, in Clttlyt, and in '/'./'.,.,/.,. 



The femur might be easily mistaken for the humerus of a niainmi- 

 ferous quadruped. Its oval head leaves the body of the bom , v. 

 being precisely separated from it, by a narrow neck. In lion of the 

 trochanter there is a transverse crest, but little elevated, scp 

 from the head by a semidrenlar depression. The middle of the hmm 

 is delicate and round, nnd the lower part compressed from before 

 backwards, widening by degrees to form the lov, . r head, which is a 

 transverse portion of the cylinder a little inflrctd haek wards. 

 Differences of modification occur in the Fresh- Water and .Marine 

 Tortoises. 



The two bones of the leg are nearly straight The tibia is larger 

 ..tnl in arly mi. ireular above, becoming again slightly larger 1- 

 the tilmla is more compressed and wider below. The fir-t 

 slightly concave uniform surface, the other one which is slightly 

 convex and rhomlioidal at the astragalus. M> . n-enr in the 



Laud-Tortoises, in Chtlyi, in Trionyx, and in the Chi 



Bones of the Fore Foot. The dil1>Teme- in the mode of prog 

 required corresponding variations in the bones of the fore and hind 

 feet especially. Accordingly we find that in the Chcltmct all the 



