xiii.] 7 HE FROG. 215 



a. A very long cylindrical bone, expanded at 

 each end. 



/3. The grooves on it; one running along the 

 whole ventral surface, but most marked near 

 the ends; other grooves on the dorsal sur- 

 face, one at the upper, another at the lower 

 extremity: these indicate that the os cruris 

 is really made up of two united bones, the 

 fibula and the tibia. When the limb is 

 stretched out at right angles to the body, the 

 tibia is anterior, corresponding with the 

 radius; and the fibula, posterior, correspond- 

 ing with the ulna. 



c. The tarsus. 



a. Two elongated bones (separate in the middle 

 but united by confluence of their cartilagin- 

 ous extremities) articulate with the ankylosed 

 tibia and fibula; the anterior, or tibial, of 

 these is the astragalus; the posterior, or 

 fibular, the calcaneum. 



/3. With the distal ends of these, two partially 

 ossified cartilages, one on the calcaneal and 

 the other on the astragalar side, articulate. 

 The latter is connected by ligamentous 

 fibres, within which a nodule of cartilage 

 may be found, with the first and second meta- 

 tarsals, and supports the calcar (d. ). 



d. The digits. Five in number; the internal one 

 the shortest, the fourth the longest. Their com- 

 position 



a. The first, or hallux (the most internal); a 



metatarsal bone, followed by two phalanges. 

 M. 15 



