THE FROG 33 



of union are known as the ischial and pubic symphyses. The 

 dorsal moiety is separated from the ventral by the acetabulum, 

 just as in the pectoral girdle the scapular half is divided from 

 the coracoid half by the glenoid, and all three bones, ilium, 

 ischium, and pubis enter into the composition of the aceta- 

 bulum. The peculiarity of the frog's pelvis consists in the 

 great relative length of the ilia, the reduction in size of the 

 ischia and pubes, and the flattening and approximation of 

 the members in the region of the acetabulum. 



The thigh-bone or femur is a long cylindrical bone with 

 a slight S-shaped curvature. The shaft is ossified; the upper 

 extremity has a rounded cartilaginous articular head placed 

 directly on the shaft; and the extremity also has a rounded 

 cartilaginous surface for articulation with the leg-bone. 



The leg of those vertebrates which have limbs with five 

 fingers or toes has typically two bones. Both are present 

 in the frog, but so firmly and intimately are they fused 

 together that they seem to form a single bone, the os cruris. 

 But, if it is cut across the middle, two cavities are seen, showing 

 that the bone is double ; and its double nature is further ex- 

 pressed by longitudinal grooves on the surface. We shall 

 therefore call it the tibio-fibula. Its upper surface has a 

 grooved articular surface for the femur, and its lower ex- 

 tremity a transversely elongated surface for articulation with 

 the ankle. 



The ankle of the frog is peculiar. Its proximal portion 

 consists of two rather long bones, separated from one another 

 in the middle ; but their extremities approach one another 

 and are bound together proximally and distally by cartilaginous 

 articular epiphyses. These two bones represent the proximal 

 row of the ankle or tarsal bones, and correspond to the 

 heel-bone (calcaneum) and ankle-bone (astragalus) in man. 

 The further row of tarsals is very much reduced, consisting of 

 two tiny pieces of calcified cartilage. One, a flat piece, lies 

 between the common epiphysis of the astragalus and cal- 

 caneum and the metatarsal bones of the foot, and is generally 

 considered to correspond to the cuboid of human anatomy. 

 The other piece is a mere nodule on the inner or astragalar 

 side, and is compared with the navicular bone of human 

 anatomy. The foot has six toes. The first is minute with 

 a very small proximal piece articulating with the navicular. 



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