68 ^ PRIMROSE ; THE ANATOMY OF THE ORANG OUTANG 
muscle undergoes considerable variation in man. Turned found in two 
instances that the flexor accessorius had an accessory muscle attached 
to it which arose from the deep fascia of the back of the leg in its lower 
third and joined below the inner margin of the flexor accessorius. In 
some instances this takes the place of the deep flexor tendon in one or 
other of the digits, the latter tendon for that toe being absent. The 
number of digits to which it is distributed in man is subject to 
considerable variation. According to Testut the muscle may be 
entirely absent in man, but this one would think a rare occurrence. 
The Tibialis posticus arose from the fibula and the tibia and the 
interosseous membrane in the upper third of the leg ; it was a very 
definite but ill-developed muscle. The muscle became tendinous at 
the level of the junction of the middle and lower thirds of the tibia. It 
then passed over the posterior aspect of the lower extremity of the 
tibia, lying there in a well-marked groove near the inner margin of the 
bone and held in place by a strong band of fibrous tissue. It was com- 
pletely separated from the other tendons at the inner ankle by this band 
and passed under it into the sole of the foot. The muscle was inserted 
into the under aspect of the scaphoid bone, a slip passing to the internal^ 
the middle, and the external cuneiform bones, and to the sheath of the 
peroneus longus tendon. It thus resembles the condition found in 
man. 
The Plantar fascia was poorly developed, in fact hardly to be recog- 
nized as a definite structure, excepting in the posterior part of the foot. 
Pick also remarks on the weakness of its development. There was a 
very dense pad of fat and connective tissue over the heel. 
Abductor hallucis arose from the inner and under part of the 
os calcis, and was inserted into the tibial side of the base of the 
proximal phalanx. This muscle is well developed in anthropoids and 
apparently in all apes. In connection with it Langer^ describes in the 
Orang a tendon which passes on to Be inserted into the terminal 
phalanx of the great toe. This he compares to the condition found in the 
hand (see page 44) and considers it the representative of the flexor 
longus hallucis of man ; in the Gorilla he finds this tendon derived from 
the flexor digitorum fibularis. The muscle as described in our Orang 
resembles that found in man. On the right side Rudolf found under- 
neath the abductor hallucis a small but very distinct muscle which 
1 Loc. cit., p, 184. 
2 Loc. cit., p. iq2. 
