270 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
dactyle animals; the oblique extensor of the metacarpus might be found 
inserted into metacarpal 1, and the flexor perforans muscle might send 
a tendon to digit 1. The pollex, if thus supplied with muscles, should be 
innervated by a branch from the radial side of the median nerve. In 
examining the following cases of polydactylism in the manus of the pig, 
we shall see whether these theoretical conditions are ever fulfilled. 
Of the thirty-six instances of polydactylism which were studied, all 
were of the manus; in every case, also, the supernumerary digit oc- 
curred on the radial side of the extremity. Digit 1 is abnormal in some 
cases. The abnormalities might be divided into numerous types accord- 
ing to the number and condition of the extra digits ; but as these types 
grade into one another, we shall attempt to distinguish but two classes : 
(1) cases in which the supernumerary parts are distinct from, and inde- 
pendent of, the normal digits; (2) cases where they are more or less 
closely connected with digit 1. We shall see that even these are artifi- 
cial groups, and that intermediate conditions link together the two. In 
the following descriptions, we shall begin with the simplest forms, and 
pass in succession to the more complex types of polydactylism. 
1. Manus in which the Supernumerary Digits are Independent of the 
Normal Digits. 
a. ONE SUPERNUMERARY DIGIT. 
The simplest example of this condition is represented by a single case 
(Plate 4, Fig. 12). Externally the extra digit (1) is inconspicuous, but 
originally bore a small claw-like hoof. It is composed of two rudimen- 
tary phalanges and a spheroidal element, which apparently represents the 
distal end of a metacarpal. This does not articulate with the second 
metacarpal, but is merely held in place by fibrous tissue and the skin. 
In the carpus the trapezium is abnormally long ; it articulates with 
the trapezoid laterally, and has a facet proximally for the scaphoid ; in 
other respects the bones of the, manus are normal. The muscles and 
nerves are unmodified. 
Figure 13 (Plate 5) shows a manus in which the pollex is fully de- 
veloped. Of this type, four cases were examined. The pollex (1) is 
smaller than digit 1 and consists of the metacarpal and two phalanges. 
The metacarpal bone articulates with the trapezium, which is abnor- 
mally large and has three facets: a distal for metacarpal 1, a lateral 
for the trapezoid, and a proximal for the scaphoid. The relations of the 
bones of this digit to those of the rest of the manus are thus identical with 
the conditions found in fossil swine and in other pentadactyle animals. 
