PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
8l 
plus the palmar portion of the dorsal interossei, and the short flexors of 
the thumb and little finger. 
The flexor brevis of the first digit is represented by two heads, of 
which the deep head might otherwise be described as one of the palmar 
or plantar interossei, the interosseus primus volaris of Henle. This 
muscle resembling in its attachments and relations the other muscles of 
the plantar interosseous group, belongs to the intermediate layer. 
The common origin of all these muscles of the interosseous group is 
indicated by Huxley^ who states that amongst the Platyrrhini the 
interossei are no longer visible from the dorsum of the foot, but, as in 
the lower mammals, are altogether flexores breves inserted by sesamoid 
bones into the bases of the first phalanges. This resembles the condi- 
tion described by Ruge in the human foetus (vide infra). 
We have still left for consideration a series of muscles representing the 
adductor group. In the Orang, as in man, these are reduced to the 
adductors for the first digit. Thus we have in the hand the adductor 
obliquus pollicis and the adductor transversus pollicis. These represent 
a more extensive series found in marsupials in the plantar layer as 
adductors of the second, fourth and fifth digits. In the Chimpanzee and 
Gibbon there are two adductors, viz., for the first and fifth digits, whilst 
in the Orang and Gorilla the adductor for the first digit alone remains. 
Thus in man and in the orang we have, in the palmar layer, the 
adductors of the thumb (obliquus and transversus). 
Adductor obliquus pollicis. 
Adductor transversus pollicis. 
The only short muscles of the first and fifth digits, which we have not 
accounted for, are of the opponens group. In my Orang we found an 
opponens for the first and fifth digits in both hand and foot. These 
Cunningham considers as developed most commonly from the flexores 
breves group. 
Our complete classification would therefore be : 
Dorsal layer. 
1. Abductor pollicis. 
2. Abductor minimi digiti. 
Loc. cit., Vol. II, p. 94. 
