76 
PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
conclusion that the flexor sublimis digitorum of the hand has as its 
homologue in the foot the flexor brevis digitorum and the soleus, the 
latter muscle having been separated from the former by the growth 
backwards of the os calcis. Again in the case of the extensor brevis 
digitorum pedis we have in the hand as homologous structures the 
extensor minimi digiti and the extensor indicis. Huxley himself^ in 
discussing these two muscles in the Orang, called attention to the fact 
that in many of the lower mammalia the normal arrangement is to have 
a superficial and a deep extensor supplied to every digit. This arrange- 
ment is approached when we find, as in my Orang, the extensor minimi 
digiti passing to the fourth and fifth digits, and the extensor indicis 
passing to the second and third digits. In the dissecting room of the 
University of Toronto, I found, in the human subject, an extensor indicis 
for the second digit, and an extensor minimi digiti for the fifth digit, whilst 
a very well developed muscular slip (i cm. wide), arose from the ligaments 
over the back of the carpus, and proceeding over the dorsum of the 
middle finger beneath the tendon of the common extensor, it split at the 
head of the metacarpal bone and blended with the extensor expansion 
on the dorsum of the proximal phalanx. This was a true extensor 
brevis occurring in the hand of man. 
The supinators (longus and brevis) do not appear to have any repre- 
sentatives in the lower limbs, nor do the two radial extensors. So, too, 
we have structures in the foot not represented in the hand, of which the 
flexor accessorius is an example. One has observed the fact that the 
foot of the ape frequently differs from the foot of man in that the 
accessorius is often absent in the former. It is usually absent in anthro- 
poids (although present on the right side of my Orang) : it is present 
however in the lower apes. Bischoff^ points out that in man it corrects 
the direction of the action of the flexor digitorum longus communis, 
otherwise the direction of the pull of the long flexor would be at an 
angle. In the foot of the ape this is of no importance, on the contrary 
the action of the flexor tendons in adducting the other toes to the great 
toe is of great service in seizing or grasping. The toes of the apes in 
their flexor arrangements would thus resemble fingers much more than 
toes. 
Although difficulties arise in the attempt to establish homologies, yet 
on the whole it would appear that a remarkable correspondence is 
obvious when we compare the musculature of the forearm with that of 
the leg. This is further evidenced in a most remarkable manner if we 
1 Loc. cit., Vol. I, p. 5q6. ' 
2 Loc. cit. I, p. 257. 
