PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
6i 
joins the extensor tendon of the little toe, derived from the extensor 
digitorum communis longus. Huxley^ describes this muscle in the 
lower apes ; he calls it the Peroneus quinti digiti. The muscle appears 
to be very uncommon in the anthropoid apes, although Bischoff thought 
that possibly a tendon coursing along the outer margin of the foot, which 
proceeds from the tendon of the peroneus brevis and is inserted with 
the extensor tendon of the little toe, might be looked upon as a rudi- 
ment of the peroneus parvus in the Gorilla. He found this tendon also 
in the Chimpanzee, as also did Gratiolet and Alix.^ This tendon has 
apparently not been found in the Orang, but Huxley^ describes in the 
Chimpanzee a muscular slip arising from the calcaneum apparently 
detached from the abductor minimi digiti, and ending in a tendon in- 
serted into the base of the fifth metatarsal bone. This, Huxley suggests, 
might be called the “ abductor ossis metatarsi quinti^ This corresponds 
precisely to the tendinous arch which I describe in the Orang in con- 
nection with the insertion of the peroneus brevis, and possibly represents 
a rudiment of the peroneus parvus. 
Fick^ has described a peroneous parvus in the Orang. Hitherto 
it was held that it did not exist in anthropoids, and apparently it is of 
rare occurrence among those apes, as this is the only instance in which 
I find its presence noted, although carefully sought for by various 
observers. 
Ruge® makes some interesting observations on the peroneal group 
of muscles. He considers that the peroneus longus tendon in the 
mammalia wanders from the anterior to the lateral part of the 
limb. Thus in carnivora it originally lies on the anterior surface of the 
fibula, in rodents the tendon at one time lies upon the lateral aspect of 
the external malleolus and at another time behind it. In the ape the 
tendon lies in a special synovial sheath separated from the brevis, whilst 
in man they lie both together in the same synovial sheath. Ruge 
evidently considers the extensor brevis digitorum to be derived from 
the peroneal group, and represents it as wandering toward the dorsum 
of the foot, as would appear by studying its relation in different mam- 
mals. In marsupials, only two bellies pass over for insertion into the 
first and second toes. In rodents and insectivora three bellies exist for 
the first, second and third toes ; and in carnivora, apes, and man, there 
1 Loc. cit., Vol. II, pp. 40, 94, 124. 
2 Loc. cit., p. 198. 
3 Loc. cit., Vol. I, p. 429. 
4 Loc. cit. I, p. 42. 
5 Dr. George Ruge, “ Untersuchung uber die Extensorengruppe am Unterschenkel und Fusse der 
Saugethiere.” Morphologisches Jahrbuch, Vol. IV, 1878, p. 592. 
