144 



FOUNDATIONS OF BIOLOGY 



toral) and posterior (pelvic) paired fins of Fishes, which merely 

 act as paddles; but when these are modified into paired limbs 

 for progression on land, the mechanical problems involve the 

 development of complex limb skeletons to support the body, 

 and to act as levers for the limb muscles to move in locomo- 



SCP 



HU 



PU 



dsb.S 

 mils. 5 



JS 



FIG. 80. Diagram of the plan of the Vertebrate limbs. A, fore limb and pectoral 

 girdle; B, hind limb and pelvic girdle; actb, socket for femur; CL, clavicle (collar 

 bone) ; en, 1-2, middle row of carpals and tarsals; COR, coracoid; dst, 1-5, distal row of 

 carpals and tarsals; FE, femur (thigh bone) ; FI, fibula; fi, fibulare (a tarsal) ; gl, socket 

 for humerus; HU, humerus (upper arm bone); IL, ilium; int, intermedium (a tarsal); 

 IS, ischium; mlcp, 1-5, metacarpals; mtts, 1-5, metatarsals; p.cor, procoracoid; ph, 

 phalanges; PU, pubis; RA, radius; ra, radiale (a carpal); SCP, scapula; TI, tibia; 

 li, tibiale (a tarsal); UL, ulna; ul, ulnare (a carpal). (From Parker and Haswell.) 



tion. In response to this need an elaborate series of bones is 

 developed which, in all cases, however, may be referred to a 

 common plan, known as the PENTADACTYL LIMB in allusion 

 to the five digits (FINGERS and TOES) in which it usually 

 terminates. The limbs are attached directly or indirectly to 



