38 
PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
whilst it would appear to be the usual condition in the Orang, as 
described by Fick, Bischoff, Huxley, Hepburn and Chapman. On the 
other hand, according to Bischoff,^ in the Gorilla, Chimpanzee and 
Gibbon, and in the lower apes (excluding Cynocephalus, where it exists 
as in the Orang), the tendon is restricted to the little finger as it is in 
man. 
The Extensor carpi ulnaris arose from the common extensor origin, 
from the olecranon process and the posterior portion of the ulna and 
from the intermuscular septum ; it was inserted into the ulnar border of 
the fifth metacarpal bone. 
The Extensor Indicis arose from the middle of the ulna by an origin 
1.5 cm. wide, and from the interosseous membrane, passing beneath the 
common extensor, it was inserted into the extensor expansion over the 
dorsal aspect of the proximal phalanx of the second and third digits. 
In man the extensor indicis is inserted into the index finger only, 
although, as a variation, it is not very uncommon to find a slip to the 
middle, or even the ring fingers, whilst occasionally there is a slip to the 
thumb. It is sometimes altogether absent in man, and TestuF states 
that he has seen it tendinous throughout its whole extent, According 
to Bischoff^ in the Gorilla alone among anthropoids do we find the 
extensor indicis restricted to the index finger and thus resembling man. 
In the Orang and Chimpanzee it passes to the second and third digits, 
whilst in the Gibbon it passes to the second, third and fourth digits. 
In the lower apes also it would appear to be distributed, as a rule, to the 
second and third digits. Pithecia being an exception (Bischoff), where it 
is restricted to the index finger only. Huxley,^ in discussing this 
muscle in the Orang along with the extensor minimi digiti, calls 
attention to the fact that the normal arrangement in many of the lower 
mammalia is to have a superficial and a deep extensor supplied to every 
digit. This arrangement is approached when as in my Orang the 
extensor minimi digiti is supplied to the fourth and fifth toes, and the 
extensor indicis to the second and third toes. These two muscles, as 
they occur in man, are therefore but fragments of a more extensive 
muscle group occurring in lower animals. 
The Extensor longus pollicis arose from the dorsal aspect of the ulna 
above the origin of the extensor indicis, and passed to its insertion in a 
I Loc. cit. I, p. 212. 
2 Loc. cit. I, Vol. I, pt. 2, p. 813. 
3 Loc. cit. I, p. 212. 
4 Loc. cit., Vol. I, p. 5g6. 
