a correct System of Muscular Homologies. 319 
by the assumption that for the typical digit there are four such 
muscles—a palmar on each side and a dorsal on each side. In 
the human manus, which we will take for illustration as the 
most familiar, we have these developed as follows. 'The pollex 
on its free side has a muscle, the abductor, which, however, is 
generally divisible into two, an abductor exterior and interior, 
so named by Sémmerring. The interior of these, undoubtedly, 
acts (as Meckel suggests) as a palmar interosseus ; this muscle 
is present in Ornithorhynchus, in the opossum, in the bear, 
Gulo, and others. On its ulnar side a muscle is occasionally 
resent as an anomaly in man, described by Henle—the 
interosseus primus volaris, which I have never found as a 
portion of the normal anatomy of any animal. Meckel, how- 
ever, in speaking of the short muscles of the thumb, says :— 
“Il y a quelquefois, par exemple chez le magot, un petit flé- 
chisseur plus profond que l’on rencontre parfois aussi dans 
Vhomme.” ‘This might perhaps be the muscle of Henle; 
and Prof. Huxley has described it as existing in the gorilla 
(Med. Times & Gazette, 1864, p. 538). For the index finger 
there is a radial palmar muscle, which in the human subject 
arises from the os magnum and the base of the third meta- 
1; but as its function as a radial lateralizer of the index 
is better fulfilled by one of the dorsal muscles, its insertion is 
shifted to the inner sesamoid bone of the pollex, and it becomes 
the deep head of the flexor pollicis. I have found this muscle 
in Hystrix cristata; and, as stated above, in Dasypus this 
muscle is present and typical, attached to the radial side of the 
index. The palmar ulnar interosseus is developed as the first 
palmar interosseus of the human hand. It is present in the 
ee of many monkeys, of the dog, and the Ornithorhynchus. 
or the middle finger the two palmar interossei, being super- 
seded in function by the dorsals, would be entirely atrophied, 
but that they are devoted to a special purpose; and hence, 
coalescing, they are inserted into the inner sesamoid bone of 
the pollex, constituting the adductor pollicis. In the dog this 
muscle is represented by a fibrous band, not truly muscular ; 
it is muscular, however, in Ursus arctos; and in some monkeys 
(as Macacus nemestrinus) it is large; in Ursus a slip of it is 
occasionally inserted into the second toe at its base, constituting 
a special adductor indicis. Nycticebus presents us with the 
intermediate state of this muscle, between the foot arrange- 
ment, to be referred to presently, and the typical human ar- 
rangement; for in this animal the accomplished anatomists 
who have given us so complete a monograph upon its myolog 
have described, besides the typical interossei, fine fasciculi 
arising from the third and fourth metacarpals and inserted into 
