PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
47 
The palmar interossei arose each by a single head from the meta- 
carpal bone of the digit upon which it acts. The first palmar inter- 
osseous muscle arose from the palmar and ulnar surfaces of the second 
metacarpal, whilst the second and third palmar interossei arose from the 
palmar and radial surfaces of the fourth and fifth metacarpal bones 
respectively. They were inserted as in man. 
The drawings (plate V) are faithful representations of the relations 
which existed, and one has reproduced in a diagrammatic fashion in 
fig. 4, plate IV, the relations of the interossei to the metacarpal bones 
as they appear in transverse section. The second, third and fourth 
metacarpal bones were thus completely surrounded by the interossei in 
the proximal two-thirds of their length. 
Bischoff described^ the interossei very fully in a large number of the 
lower apes and the anthropoid apes. He recognized the fact that there 
existed a palmar set of interossei as distinct and independent muscles. 
They vary in the number present in the different apes, but never exceed 
three, and were always developed in connection with the second, fourth 
and fifth digits. The double insertion of the various interossei, both 
palmar and dorsal, whereby they are on the one hand attached to the 
base of the proximal phalanx and on the other into the extensor 
aponeurotic expansion on the back of the phalanx, was first pointed out 
by Huxley^ in anthropoid apes. The interossei and their attachments 
were fully described by Huxley in all four anthropoids. Bischoff found 
the interossei in the Gorilla developed as in man.^ 
The palmar portions of the dorsal interossei formed such very definite 
structures in my Orang that they attracted special attention. This 
segment of the dorsal interosseous muscle in fact resembles a palmar 
interosseous muscle, but this ventral segment is blended very intimately 
with the dorsal in the tendon of insertion of the muscle. The palmar 
interossei on the other hand remain independent structures through- 
out. This condition is very similar to that found in man, and, obviously, 
the description in most text books of human anatomy regarding these 
muscles is faulty. Gegenbaur,^ however, describes and figures them in 
their correct relations. HepburiT apparently found these ventral seg- 
ments of the dorsal interossei, and, if I read his description aright, looked 
1 Loc. cit. I, pp. 216, 224. 
2 Loc. cit., Vol. I, p. 456. 
3 Loc. cit. 2, p, 17. 
4 C. Gegenbaur, “ Lehrbuch der Anatomie des Menschen.” Leipzig. Vol. I, p. 431. fig. 303. 
5 Loc. cit., p. 174. 
