PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 281 
second phalanges and forms a sheath for each division of the perforans 
tendon. The innervation is shown in Figure Q. 
With the increase in size of the extra digits of the polydactyle series, 
goes a corresponding decrease in the size of digit 1. It is apparently 
reduced, and partially, sometimes completely, atrophied on account of 
the abnormal development of the supernumerary parts. In a case fig- 
ured by Bateson (’94) the middle portion of metacarpal 1 is gone. In 
two front feet, from a single animal, I found that the left manus was 
like that shown in Figure 20, the trapezoid and proximal end of meta- 
carpal 11 being reduced; in the right manus, however, metacarpal 1 
was completely atrophied, but the three phalanges persisted and were 
of nearly normal size. The trapezoid remained asa small flattened bone, 
articulating chiefly with metacarpal 11. The reduction is carried a 
step further in another case, in which the three phalanges of digit 1 
are present, but exceedingly small, and the hoof reduced to a claw-like 
vestige (Plate 14, Fig. 22, 11). 
The nerve branch which normally supplies the second digit innervates 
this vestige (Fig. 7, 2), making it reasonably certain that we have to do 
with the rudiment of digit 11. 
Figure 23 (Plate 15) represents the skeletal parts of a manus in 
which the second digit has apparently atrophied completely. Three 
Specimens were examined which exhibited this condition. Such cases 
have been described as duplications of digit 11, but a careful study of 
the manus shows that this is not the case. If we compare Figure 23 
with Figure 22, the resemblance between the skeletal parts of the extra 
digits is striking. In each case they both articulate with the trapezium, 
and digit 1° has taken nearly complete possession of the distal facet of 
the trapezoid, which is normally occupied by digit 1. The trapezoid 
itself is narrow and smaller than the trapezium ; the scaphoid in Figure 
23 is divided into two elements, a condition which is found only when 
two large functional digits are added to the normal number. Other im- 
portant facts are that digits 1* and 1” are of nearly equal size, symmet- 
trical with reference to each other, and bear hoofs which are connected 
posteriorly by a pad of horn. 
The musculature and nerves also afford good evidence in favor of this 
interpretation. The tendons which are normally inserted into the sec- 
ond digit are wanting here. The second branch of the median nerve 
(Fig. U, 2), which normally supplies digit 11, still sends a large branch 
to the radial side of digit ur and may thus be identified. But dissec- 
tions failed to disclose the small nerve which usually supplies the second 
