EXPLANATION OF PLATE XII. 



Fig. 1st. Skeleton of a Tortoise, with the under part (sternum or plastron,) 

 removed to show how the back-bone and ribs are expanded and uni- 

 ted together, forming the carapace, dorsal plate, or buckler. 



H. The three-branched shoulder. I. Humerus, between the shoul- 

 der-joint and the elbow. K. Ulna. L. Radius, both bones of the 

 fore-arm. R. Femur, or the thigh bone. S. Tibia, the largest, and 

 Fibula, the smallest bones of the leg. 



Fig. 2d. Skeleton of a Bird, consisting of A. Cranium or Skull. B. Cer- 

 vical vertebrae. C. The anchylosed or immovably fixed vertebrae of 

 the back. D. The caudal vertebrae. E. Ribs. F. Breast-bone. G. 

 Furcula, or merrythought. H. Clavicle, or collar-bone. H*. Scapula, 

 or shoulder-bone. I. Humerus. K, L. Bones of the fore arm, ulna, 

 and radius. M. Metacarpus of hand. N. Phalanges of fingers. R. 

 Femur, or thigh-bone, o, o. Patella, or knee-pan. S. Leg, tibia 

 and fibula. T, T. Os calcis, or heel-bone. U, U. Metatarsal bones. 

 V, Y. Metacarpal bones. 0. Ilium. P. Pubis, and Q. Ischium, bones 

 of the pelvis. 



Fig. 3d. Skeleton of a Fish, showing the five sorts of fins, some of which 

 are often absent, a, b, first and second dorsal fins on the ridge of the 

 back, varying in number and form ; c, the caudal or tail fin, as impor- 

 tant to a fish as the rudder to a ship ; d, anal fin, on the under part 

 of the tail ; e, one of the ventral fins which correspond to tke hind 

 feet of quadrupeds ; f, one of the pectoral fins, which are analogous to 

 the fore feet of quadrupeds, or the wings of birds. 



Fig. 4th. Skeleton of a Frog, showing the absence (or mere rudiments,) of 

 ribs, and its long hind limbs adapting it for sudden springs and long 



Fig. 5th. Skeleton of a Boa-constrictor, consisting of skull, a ; vertebral col- 

 umn, b ; and ribs, c. The ribs, 304 in number, come forward in succes- 

 sion, like the feet of a caterpillar, and form 152 pairs of levers by 

 which the animal moves from place to place. The jaws, d, have 

 on each side, a double row of sharp, strong, close-set teeth, pointing 

 backwards, thus giving a firm hold of its victims. 



Fig. 6th. Skeleton of a Chameleon, showing how the toes and tail are 

 adapted for clinging to the branches of trees, and that the trunk is 

 mounted high upon the legs, forming in this respect an exception to 

 most reptiles. 





