LIMBS 359 



according to their position, radiale, intermedium, and ulnare.^ 

 The second row contains in the early stages of its development 

 five bones, called distal carpals, corresponding to five digits, 

 but in the adult frog the third, fourth, and fifth of these have 

 fused. The palm contains five metacarpal bones. The first digit 

 is wanting, but the second and third have each two bones and 

 the fourth and fifth three, according to the number of their joints. 

 These bones are called phalanges {singular phalanx) and they may 

 be represented by the conventional formula 02233. 



The bones of the leg correspond closely to those of the arm. 

 The thigh-bone or femur has a long, slender, sHghtly sigmoid 

 shaft with a rounded head to fit into the acetabulum and a wide 

 condyle for articulation with the shank-bone, or tibiofibula. The 

 latter, Uke the radio-ulna, corresponds to two bones in man and 

 many other animals, showing traces of being formed by the 

 fusion of an inner or anterior shin-bone or tibia and an outer or 

 posterior fibula. The ankle, Hke the wrist, consists of two rows of 

 bones, which are here called tarsals. The first row contains two 

 bones, the tibiale, and the heel-bone or fibulare.^ These bones 

 are joined at each end by a piece of cartilage. The second row 

 consists of two small distal tarsals. The metatarsus contains six 

 metatarsals, one minute and corresponding to a small extra toe, 

 the prehallux or calcar, which hes inside the first toe or hallux, 

 but does not project from the foot. The numbers of phalanges 

 beginning with that for the calcar, which is put in brackets, are 

 (1)22334. 



LOCOMOTION 



The arrangement of the chief muscles of the frog is shown in 

 Figs. 274 and 275. 



It would not be possible here to describe the various modes of 

 locomotion of the frog, even if they were at present thoroughly 

 understood. Something must, however, be said about crawling, 

 in which the frog practises what is the primary mode of locomotion 

 of four-footed animals. In it the body is levered forwards over the 

 ground by the hmbs, which are used in diagonal pairs, the left 

 hind-limb immediately after, or practically with, the right fore- 

 limb, and similarly the right hind-limb with the left fore-limb. 

 Fig. 276 shows a toad moving in this way. 



1 For other names of the bones of wrist and ankle see p. 556. 



