224 ELEMENTARY BIOLOGY. [CHAP. 



y. The third digit: a metacarpal bone with two 



phalanges. 

 8. The second digit : a metacarpal bone with two 



phalanges. /. . . ' 

 c. The first digit (pollex) consists only of a 



small metacarpal bone. 



g. The pelvic girdle. 



a. Its general form : V-shaped, with the apex 

 turned backwards. 



b. The concavity (acetabulum) on each side with 

 which the thigh-bone articulates. 



c. The triradiate fissure running through the aceta- 

 bulum and dividing each half of the pelvis into 

 three pieces, viz. 



a. An anterior elongated piece (ilium) subcy- 

 lindrical in front, where it articulates with 

 the sacrum ; bearing behind, on its dorsal 

 aspect, a laterally compressed ridge of bone 

 (crista ilii)', it forms almost half of the aceta- 

 bulum. 



/?. A posterior, irregularly rounded piece (is- 

 chium)-, closely united posteriorly with its 

 fellow, in the middle line. 



y. A small triangular piece (os pubis), (calcified 

 cartilage except in old frogs), wedged in 

 between ilium and ischium, and meeting its 

 fellow in the median ventral line, thus form- 

 ing the symphy sis pubis. 



h. The bones of the lower limb 



a. The thigh-bone (os femoris); its long cylindrical 

 shaft and expanded articular extremities. 



b. The leg-bone (os cruris). 





