10 



MAMMALIA 



Mammalian Carpus. 



Scaphoid 



Lunar 



Cuneiform 



Pisiform 



Central e 



Trapezium 



Trapezoid 



Magnum 



Unciform . 



Reptilian Carpus. 



Radiale. 

 Intermedium. 

 Uluare. 

 Pisiform. 

 Ceutrale. 

 Carpale I. 

 Carpale II. 

 Carpale III. 

 Carpale IV. i 



Of the above the pisiform is a bone, which is by some considered the 

 representative of a sixth finger, by others a sesamoid bone. The pisiform is 



well represented in Per- 

 mian reptiles and amphi- 

 bians. The centrale often 

 fuses Avith the scaphoid. 

 The second centrale of 

 reptiles is apparently lost 

 in mammals. In the 

 primitive carpus all these 

 bones remain separate, 

 the arrangement being 

 more alternate than serial. 

 Where weight has to be 

 [td supported, the carpus is 

 usually rearranged in 

 various ways. For this 

 the upper row becomes 

 more compact, the lunar 

 and scaphoid often fusing; 

 Avhile fusions of adjacent 

 bones take place in the 



A, \j&it vasLxms ot Procavia {Dendrohyrax) arborea. B, Tapinis Ameri- ■, i A <-l, 



amus. C, Riglit manus of the horse. R, Radius ; U, ulna; s, scaphoid ; iower rOW alSO. AnOtncr 



/, lunar; c, cuneiform; «, pisiform; ce, centrale; tm, trapezium; td, rnnrlo r\f ofr-orxTt-Vioninrr ia 



trapezoid; m, magnum; H, unciform; /.-K., digits. moue OI bOiengUUening lb 



seen among ungulates, 

 where the distal row of bones is rearranged so as to alternate with the upper 

 row, and thus make a more compact joint. The same result is attained by 

 the expansion of a wrist bone, for example the magnum (Fig. 10, C). The 

 lateral expansion of a distal carpal bone, in connection with the loss of the 

 first digit, often causes the entire suppression of the trapezium. 



Beyond the carpals come the metacarpals, one opposite each carpal, except 

 the unciform which supports metacarpals IK and F. Originally the articular 

 ends of the metacarpals made an even row, but individual bones have pressed 

 into the carpal row making an uneven but much stronger articulation. The 

 distal rounded articular facets are often divided by a sharp ridge into two 

 surfaces. 



Of tlie five digits the first, inner, or radial one is often termed the thumb 

 (pollex). With the exception of whales, no mammal has more than three 

 phalanges to each digit. The first and fifth digits often lack one or two joints. 



Fig. 10. 



' Carpale V. is much reduced in many early reptiles, and probably disappeared in the mam- 

 malian manus. 



