488 The Phylogeny of the Palmar Musculature 
bases of their metacarpals and are inserted one into either side of the 
base of the proximal phalanx of the same digit. In the case of the 
pollex, however, the arrangement of the slips is similar to that occur- 
ring in the minimus, one of them (Fig. 7, fbp,,) passing across the 
intermetacarpal interspace to be inserted into the radial side of the 
base of the proximal phalanx of the index, uniting with the radial 
shp of the flexor brevis profundus of the index and with the first 
intermetacarpal, while the other (fbp,) passes directly distally to be 
inserted into the ulnar side of the phalanx of the thumb. In this digit, 
as in the minimus, the oblique muscle has been overlooked by Young 
and Brooks, or rather has been considered to be a part of their dorsal 
layer, while the other is identical with the ulnar slip which they ascribe 
to the thumb. Their radial slip is, I believe, a portion of the flexor 
brevis pollicis and, consequently, belongs to the flexor brevis super- 
ficialis. 
The intermetacarpales are distinctly muscular, thus differing from 
those of the lacertilia which are throughout converted into hgaments. 
The second, third and fourth intermetacapals (Fig. 7, 7m) arise each 
by two heads from the sides of adjacent metacarpals near their dorsal 
surfaces and converge to a tendon (im*) which passes distally in the 
intermetacarpal space and finally bifurcates to be inserted into the 
adjacent sides of the neighboring proximal phalanges, the radial branches 
of the third and fourth tendons uniting with the tendons of the flexor 
brevis profundis slips inserted into the corresponding phalanges, while - 
the ulnar branch of the second tendon similarly unites with the radial 
slip of the flexor brevis profundis of the third digit. What I take to be 
the first intermetacarpal (im*) differs from the others in that it arises 
by a single head from the first metacarpal and is situated more volarly 
than its fellows. It passes obliquely across the first intermetacarpal inter- 
val to unite with the ulnar slip of the fiexor brevis profundus of the 
pollex and the radial slip of the same muscle of the index and inserts 
with them into the proximal phalanx of the index. 
In the cat an arrangement of the flexor profundus muscles comparable 
to that occurring in the opossum is readily discerned, but the intermeta- 
carpals are not in all cases so distinctly separated from the muscles with 
which they unite. In the fifth digit one finds the ulnar muscle dividing 
into two slips (Fig. 8, fbp;) which are inserted into either side of the 
base of the proximal phalanx; the radial muscle (fbp °), however, passes 
across to the proximal phalanx of the annulus. This digit, the medius 
and the index each possesses two slips, those of the annulus and medius 
having undergone a distal recession so that they arise from the shafts 
