126 



COMPARATIVE ANATOMY 



tremities, the anterior undergoing the most varied adaptative 

 modifications, and giving rise to tactile, prehensile, or flying organs 

 or, as in aquatic Mammals, becoming once more converted into 



rowing organs. The limbs of all 

 the higher Vertebrata may, how- 

 ever, also be reduced to a single 

 ground-type. 



The fore- and hind-limbs show a 

 great similarity as regards the form 

 and position of their various parts. 

 A division into four principal sec- 

 tions can always be recognised : 

 in. the case of the fore-limb these 

 are spoken of as upper arm (brack- 

 ium), fore-arm (antibrachium), wrist 

 (carpus), and hand (manus) ; and 

 in the hind-limb as. thigh (femur), 

 shank (cms), ankle (tarsus), and 

 foot (pes) (Figs. 105, 106). The 

 bone of the upper arm (humerus) 

 and of the thigh (femur} is always 

 unpaired, but two bones are present 

 in the fore-arm and shank. The 

 former are called radius and ulna, 

 and the latter tibia and fibula. The 

 hand and foot are also respec- 

 tively divisible into two sections, a 

 proximal metacarpus and metatarsus, 

 and a distal series of. phalanges, 

 which form the skeleton of the 

 fingers and toes (digits). 



Both manus and pes are made 

 up of several series of cylindrical 

 bones. There are never more than 

 five complete series, which except 



FIG. 105. SKELETON OF THE RIGHT 

 FORE-ARM, CARPUS, AND HAND 

 OF Salamandra maculosa. (From 

 above. ) 



JR, radius ; 7", ulna ; r, radiale ; i, 

 u, intermedio-ulnare ; c, cen- 

 trale ; 1 to 4, first to fourth 

 carpalia (according to Emery, 



l corresponds to the carpal of as regards number present essen- 

 the prepollex and 2 to the tially similar primary relations 

 common carpal of digits / and , i i , i i i '-\r , i 



//) ; Me, Me, metacarpals ; throughout the higher Vertebrates. 

 Ph, phalanges ; 7 to IV, first The skeleton of the carpus and 

 to fourth fingers. tarsus, each of which always consists 



of a series of small cartilages or 



bones, shows much variation; but the following may be taken 

 as a ground-type (Figs. 105 and 106). Round a centrale, which 

 may be double, is arranged a series of other elements, of 

 which three are proximal, and a varying number (four to six) 

 distal. The proximal, in correspondence with their relations 

 to the bones of the fore-arm and shank respectively, are spoken of 

 as radiale or tibiale, ulnare or fibulare, and intermedium ; while the 



