PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
59 
invariable ; in this respect it may be compared to the extensor ossis 
metacarpi pollicis in the hand. 
The Extensor longus hallucis arose from the upper fifth of the fibula 
and from the interosseous membrane, the line of origin being very 
short, and was inserted into the great toe, with similar relations to those 
in man. Fick^ observed in an Orang a tendon given by this muscle to 
the second toe. Bischoff states that in all apes this muscle resembles 
that of man, but, except in the Gibbon, it does not extend along the 
dorsum of the foot as in man, but goes with the tibialis anticus to the 
inner side (the latter muscle being attached to the internal cuneiform), 
and runs along the inner margin of the foot to the first phalanx. The 
muscle must in its direction act on the great toe as an abductor as 
well as an extensor. In the Gibbon alone the tendon runs a course 
similar to that in man. 
The Extensor longus digitormn arose from the internal tuberosity of 
the tibia and the intermuscular septum, also from the head of the fibula 
and the interosseous membrane, the origin being only 1.5 cm. wide. It 
was inserted into the four outer toes. 
Extensor brevis digitorum arose from the outer and superior surfaces 
of the os calcis. It was closely associated at its origin on the outer 
side of the foot with the insertion of the peroneus brevis. It was 
inserted into the four inner toes, having a similar relationship to the 
extensor longus digitorum as in man ; that for the great toe formed a 
separate and distinct muscle, running almost at right angles to the main 
part of the muscle, and passed to the great toe with the extensor longus 
hallucis. Duvernoy^ describes this slip in the Gorilla as a separate 
muscle of the great toe. Langer® describes in the foot a similar 
interdigital membrane to that found in the hand, the toes being 
thus even more sunken in the foot than are the fingers in the hand. 
The Peroneus tertius was absent, as is the case apparently with all 
apes, both the anthropoids and the lower apes. This muscle is peculiar 
to man among mammals, and there is some evidence that its develop- 
ment has to do with the erect attitude assumed by man. Ramsay 
Smith^ believes that it serves an important function in preventing- 
spasmodic extension of the ankle joint in ordinary walking. This, 
according to Smith, occurred in cases where the muscle was paralysed. 
1 Loc. cit. 2, p. 303. 
2 Loc. cit., p. 103. 
3 Loc. cit., p. 190. 
4 W. Ramsay Smith, “ The Functions ot the Peroneus Tertius Muscle.” Edinburgh Medical Jour- 
n.al, 1882, p. 632. 
