40 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, but 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 
Fic. 31.—Bones of fore-arm arranged in their proper order, beginning 
and manus of Mole (Tape ith that on the radial side of the limb, 
europaea). x 2. c, Cunei- 
form ; ce, centrale; /7,lunar; that side which bears the first digit. A 
m, magnum; p, pisiform; — 1 row articul: Rove ek Pale itl 
R, radius ; rs, radial sesa. Second row articulates proximally with 
moid (falciform) ; s, sca- these bonelets and distally with the meta- 
phoid ; ¢d, trapezoid ; tm, ei 3 
trapezium; U, ulna; u, Carpals; the bones composing it are, men- 
unciform ; -Y, the digits. tioning them in the same order, trapezium, 
(From Flower’s Osteology.) Sh aa 
trapezoid, centrale, magnum, unciform, 
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, 
