58 
PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
A strong fascia covered the muscles of the calf The anterior annu- 
lar ligament of the ankle-joint was a well-developed structure consisting 
of two distinct bands, the upper passing from the internal malleolus 
outwards to be attached to the lower part of the fibula ; the lower hav- 
ing a broad attachment to the external malleolus, becomes somewhat 
narrowed as it is attached to the fascia on the inner side of the foot 
below the internal malleolus. The external annular ligament too was 
well developed as it passed over the peronei muscles, as was also the 
internal annular ligament over the structures at the inner ankle. 
The Tibialis anticus arose from the anterior aspect of the upper half 
of the tibia, from the external tuberosity and the interosseous mem- 
brane, and from the fascia over the muscle. The muscle became tendi- 
nous immediately above the ankle, where two tendons are readily 
distinguishable. The smaller one, which arose from the fleshy fasciculi 
of the anterior and outer part of the muscle, was inserted into the base 
of the first metatarsal bone at the junction of the inner and plantar 
surfaces. The larger tendon (three times the size of the former) was 
inserted into the internal cuneiform bone. The slip inserted into the 
first metatarsal bone acts as a strong abductor of the great toe, as does 
also the extensor longus hallucis. 
The tibialis anticus in certain of the anthropoid apes is more or less 
completely divided into two muscles. In man we have a single muscle, 
and a single tendon which, however, divides at its extremity to be 
inserted into the internal cuneiform and the first metatarsal bone. This 
double insertion in man is an indication of the complete separation into 
two portions occurring in some apes. In the Orang and Chimpanzee 
Bischoff^ found this division complete, and, in fact, in the Chimpanzee 
he found a third tibialis anticus arising in common with the extensor 
longus digitorum, but completely separated from it, and dividing into 
two tendons at the ankle to be inserted into the inner margin of the 
foot. In the Gibbon, Bischofif found a single muscle with a single ten- 
don passing to the internal cuneiform bone. Huxley,^ however, found 
a double insertion of the muscle in that animal. In the Gorilla, Bis- 
choff^ and Duvernoy'^ describe the muscle as in man, its tendon 
dividing for insertion into the first metatarsal and the internal cunei- 
form. In all other apes, Bischoff asserts, the tibialis anticus is double. 
It would appear, therefore, that in all apes the double insertion is almost 
1 Loc. cit. I, p. 227. 
2 Loc. cit., Vol. I, p. 648. 
3 Loc. cit. 2, p. 21. 
4 Loc. cit., p. 94. 
