266 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
only a single facet on its distal end and articulates with metacarpal u. 
The pollex is present and is represented in the figure by metacarpal 1. 
Digits 1 and v are relatively large, especially at their proximal extrem- 
ities ; 11 is better developed than v, and occupies the whole distal sur- 
face of the trapezoid. It also articulates by a small facet with the 
os magnum. 
The third metacarpal is longer than any of the others and proximally 
there is no radial process for articulation with the trapezoid. In general 
we may say that the digits of the fossil swine are confined chiefly to 
their own carpal bones, while in the pig of the present day the third 
metacarpal has developed a radial process which articulates with the 
trapezoid and has partially crowded out digit 1. In the same way 
metacarpal 1v has encroached upon the distal articular surface of the 
unciform, and pushed the fifth digit to one side; the third and fourth 
digits thus come to occupy most of the carpo-metacarpal articulation in 
the modern pig, a condition of evident advantage, as it strengthens the 
joint between the carpus and the functional digits. 
If complete reversion occurs in the skeletal parts of the pig’s manus, 
we should expect to find (1) an extra digit of two phalanges articulating 
with the trapezium, and (2) metacarpals 1 and m1 articulating with their 
proper carpal bones (trapezoid and os magnum respectively) ; (3) meta- 
carpal 11 should be longer than 1v, and without a radial process, and 
(4) digits m and v should be relatively larger than in the normal manus. 
The normal musculature of the manus is quite complex. We need 
mention here only those muscles which in the polydactyle manus pre- 
sent variations from the normal. Anteriorly we have (1) the radial or 
great extensor of the metacarpus (Fig. H, ext. mt’carp. mag.). This is 
a large muscle and is inserted by a strong tendon into the proximal 
end of metacarpal m1; (2) the ulnar or oblique extensor of the meta- 
carpus (Fig. H, ext. mt’carp. ob.), a small muscle, the tendon of which 
crosses that of the magnum obliquely, and is inserted into the proximal 
end of metacarpal 11; (3) the extensor communis digitorum internus 
(eat. com. dg.i.), a large muscle inserted by means of three tendons. 
The main tendon bifurcates, the radial portion being inserted in the 
third phalanx of digit 1; the remaining portion of the tendon runs 
some distance and again bifurcates, the two branches becoming attached 
to the ungual phalanges of the third and fourth digits ; (4) the extensor 
proprius internus (eat. prp. 7.), a much smaller muscle than the preceding, 
is inserted by two tendons, the larger going to the radial side of the third 
digit, the smaller to the ungual phalanx of m; (5) extensor proprius 
