294 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
has shifted toward the ulnar side. The supernumerary metacarpal (11) 
is the smallest of the three; it is fused to mr throughout its whole 
length, and can be traced to the proximal extremity of the metacarpus, 
where it takes part in forming the articular facet for the carpals. The 
distal epiphysis extends beyond those of 
the normal metacarpals, has a flattened 
instead of a convex articular surface, and 
no trochlear ridge. The fifth metacarpal 
“> ext, com. dg. (Fig. W, v) is, as normally, a rudimentary 
stylet articulating at the ulnar side of the 
proximal extremity of Iv. 
All three digits are composed of three 
phalanges. Digit rv is apparently normal ; 
digit 111 is more massive, and the sym- 
metry of its phalanges and hoof is affected 
by the presence of the abnormal digit. 
Instead of being optical images of those 
of digit tv, these bones are indifferent in 
--- xt. PIP. Ue 
their conformation, curving neither to the 
right nor to the left. The hoof in which 
the ungual phalanx is enclosed is common 
also to digit mu. The extra digit (11) is 
shorter and not so massive as the normal 
ones ; its ungual phalanx is flattened lat- 
erally, and more pointed than the normal 
phalanges ; the sesamoids are absent. 
Dissection of the musculature of this 
1 Ul. Iv. manus shows that the flexors are entirely 
Fia. W.— Anterior view of the 
left polydactyle manus of a calf, : : 
showing the extensor muscles. u, important modification. The tendon of the 
supernumerary digit; v, metacar- extensor proprius internus (Fig. W, eat. 
pal of digit five; ext. com. dg., - Se aes Q 
extensor communis digitorum ; ezt. PP. t.) divides, and the more radial of the 
prp. ex., extensor proprius exter- two slips thus formed is inserted into the 
nus; eat. prp. 2., extensor pro- 
prius internus. 4 natural size. 
normal ; the extensors, however, exhibit an 
second and ungual phalanges of the super- 
numerary digit. Before its insertion this 
tendon is joined by a division of the suspensory ligament. The anatom- 
ical relations of this tendon thus resemble the normal condition in 
four-toed animals. If the supernumerary digit is a duplication of digit 
1, we should expect to find the extensor communis digitorum (eat. 
com. dg.) and the flexor tendons bifurcated ; but they are unmodified. 
