DIGGING FOOT OF MOLE 



CHAP. 



Horse. The fact that it is occasionally met with in Man is an 

 additional proof of the, in many respects, ancient structure of the 

 highest type of Primate. 



The radius and the ulna, which together constitute the fore- 

 arm, are both present in a large number of mammals, btit the 

 ulna tends to vanish in the purely walking and digitigrade 

 Ungulates, being present, however, in the 

 more ancient forms of these Ungulates. 

 In Man and in many other mammals 

 the radius can be moved from its normal 

 position and crossed over the ulna ; this 

 movement of pronation has been per- 

 manently fixed in the Elephant, where 

 the bones are crossed but cannot be altered 

 in position by the contractions of any 

 muscles. Other types agree with the 

 Elephant in this fixation of the two bones. 

 The bones of the wrist show great 

 variation among mammals. The greatest 

 number present are to be seen in such a 

 type as the Mole. % Here we have a 

 proximal row, consisting of the scaphoid, 

 lunar, cuneiform, and pisiform, which are 

 FIG. 31. Bones of fore-arm arranged in their proper order, beginning 

 X-rx 2 M01 :,S with that on the radial side of the limb, 



form ; ce, centrale ; I, lunar ; that side which bears the first digit. A 

 in, magnum; , pisiform; -. ,. -, , n -,i 



R, ralius ; , radial sesa- second row articulates proximally with 

 moid (falciform) ; s, sea- these bonelets and distally with the meta- 



phoid ; td, trapezoid ; tm, , t . , ... 



trapezium ; u, ulna ; u, carpals ; the bones composing it are, men- 

 uncitbrm; i-v, the digits, tioning them in the same order, trapezium, 



(From Flowers Osteology.) . 



trapezoid, centrale, magnum, unciiorm. 



The centrale does not, however, really belong to the distal 

 carpal row, and is as a rule situated in the middle of the carpus 

 away from articulation with the metacarpals. It is a bone which 

 is not commonly present in the mammalian hand, but is present 

 in various lower forms, such as the Beaver and Hyrax. It also 

 occurs in such high types as the majority of Monkeys ; it is to 

 be found in the Human foetal carpus. Many extinct forms 

 possessed a separate centrale. Its importance in the formation of 

 the interlocking condition of the Ungulate foot is referred to later, 



