284 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
The other skeletal elements of this manus are normal. The muscula- 
ture and innervation are identical with the conditions shown in Figures 
Q, FR, and 8. 
2. Manus in which the Supernumerary Parts may be more or less closely 
connected with Metacarpal LI. 
a. OnE SUPERNUMERARY DIGIT. 
This condition was observed in five cases. From a typical example 
(Plate 17, Fig. 25) it might be inferred that all these cases were to be 
interpreted as mere duplications of digit 1. The extra digit (1) pos- 
sesses three phalanges and is of the same size as 11. Both are borne 
on the same metacarpal, which is large and has two articular condyles 
at its distal end. The digits, however, are not symmetrical with each 
other, as we should expect if they had resulted from duplication of 
digit 11; in both, the hoofs and ungual phalanges are concave on the 
ulnar, convex on the radial side. In the carpus the trapezium 1s 
larger than normal, and articulates above with the scaphoid, and below 
with the radial portion of the proximal facet of metacarpal 1. This 
condition is represented by only a single case. In four other specimens 
the skeletal parts exhibited very interesting conditions which serve to 
connect this class of abnormalities with the first part of the series we 
are describing. In Figure 26 (Plate 18) it is seen that the extra 
digit (1) is much larger than the second (11), but, as in the preceding 
case, both are borne on a single large metacarpal. They are not sym- 
metrical with each other, and on examining carefully the metacarpal, 
a dark irregular line will be seen, running nearly the whole length of 
the bone and dividing it into two unequal portions. This line of separa- 
tion, so clearly brought out in the skiagraph, is not, of course, a surface 
marking but represents a complete bony septum. The two components 
into which the metacarpal is thus divided, correspond in size with the 
digits which they respectively bear. 
The structure of the carpals furnishes important evidence as to 
whether the extra digit is formed by the splitting of mu. If this were 
the case, the trapezoid should show signs of duplication, while the tra- 
pezium should remain normal. On the contrary the trapezium is large 
and fused to the trapezoid. Comparing Figure 26 with Figure 17 
(Plate 9), the similarity of the skeletal structures is striking, and we 
can but conclude that the manus shown in Figure 26 differs from that 
shown in Figure 17 only in the fusion of its trapezium and trapezoid, 
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