84 
PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
chofif in the Gibbon, however, describes a hollowed out socket in the 
trapezium for the head of the metacarpal bone, but says the joint was 
not a true saddle-shaped articulation. 
The flexor accessorius is a characteristic feature in the human foot. 
We have already noted the fact that it is very frequently absent, and 
always ill-developed in the anthropoid apes. When we consider that 
its development is almost universal among the lower apes, it is not to be 
looked upon as an essential difference between man and apes ; when 
absent, however, the inferior extremity of the anthropoid ape rather 
resembles the hand of man than his foot. 
The strong well developed flexor longus hallucis is a characteristic 
feature of the human foot not found in apes. The Gorilla is an exception 
to this statement, as Bischoff and Duvernoy found a well developed strong 
tendon for the great toe in that animal. In the Orang the flexor longus 
hallucis gives no tendon to the great toe, whilst in other apes its distri- 
bution is mainly to the third and fourth toes, with usually a very weak 
slip for the hallux. 
Whilst the ape’s foot thus differs from the foot of man, it is also quite 
obvious that the hand also differs in a marked degree from the human 
hand. Compare (see photograph) the long thin hand of the ape with that 
of man, and note particularly the rudimentary thumb. The thumb is ex- 
tremely rudimentary and ill-developed. It becomes still more so in the 
new world monkeys, according to Huxley^; in Ateles it is apparently 
functionless, although all its muscles (abductor, adductor, flexor brevis 
and opponens) are present, except the long flexor. In the Arcto- 
pithecini (marmosets) Huxley^ says it can no longer be called a thumb ; 
the digit lies on the same plane as the other digits and is not in the least 
degree opposable — this might be called a paw rather than a hand — 
whilst such is the case, the hallux, which is very small, is still slightly 
opposable in this animal. 
The absence of a flexor longus pollicis, so strongly developed in man, 
is obviously a very marked and essential difference observable in com- 
paring the hand of the ape. Again we have noted the absence of the 
characteristic saddle-shaped articular surface in the joint between the 
first metacarpal and the trapezium. 
A fact of some interest regarding the comparisons which may be 
I Huxley, “ Manual of Anatomy ot Vertebrated Animals,” New York, 1872, p. 396. 
2 Loc. cit., Vol. II, p. 124. 
