72 
PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
pletely surrounded by the second and third dorsal interossei, with the 
exception of a narrow strip in the middle line on the dorsal aspect of 
the bone which is free from muscular fibres. 
The fourth dorsal interosseous muscle arose in a similar fashion from 
the fourth and fifth metatarsal bones, but the third plantar interosseous 
takes the place of the plantar part of the fourth dorsal interosseous on 
the inner and plantar surfaces of the fifth metatarsal bone. The plantar 
portion of the second dorsal interosseous muscle is, in like manner, 
replaced by the first plantar interosseous on the second digit. The 
plantar portion of the third dorsal interosseous muscle is in like manner 
replaced by the second plantar interosseous muscle in relation to the 
fourth digit. 
The first dorsal interosseous muscle is very powerfully developed. Its 
origin from the first metatarsal bone, however, is confined to the base of 
the bone. Some slips of origin from the internal cuneiform also join 
this head. The outer head of this muscle has an extensive origin from 
the second metatarsal bone, completely covering that bone, in fact, on 
its inner surface, and extending to the middle line on its plantar and 
dorsal surfaces, meeting on the plantar surface with the first plantar 
interosseous. Between the two heads of this muscle the dorsal vessels 
pass to the dorsum of the foot. 
Fick^ describes the intereossei in the Orang as like those found in man. 
In both man and apes one finds that one digit in both hand and foot 
possesses an insertion of two dorsal interossei, whilst the remaining digits 
possess only one dorsal interosseous muscle. In man it is the third digit 
in the hand, and the second digit in the foot; whilst, in my Orang, it was 
the third digit in both hand and foot In this respect, the foot of niy 
Orang corresponded to the hand of either ape or man, and differed from the 
foot of man. Abduction or adduction in the foot of my Orang was from 
or to the third digit. Bischoff, in his first paper, asserts^ that in all 
apes the arrangement of the interossei of ^he foot corresponds to the 
hand of man and apes ; but, subsequently, he found in the Gorilla an 
arrangement corresponding to the foot of man. Hepburn^ found that 
abduction of the digits of the foot was from a line drawn through the 
second digit in the Gorilla and Chimpanzee, whilst in the Orang and 
Gibbon it was from a line through the third digit, as in my Orang. 
1 Loc. cit. I, p. 47. 
2 Loc. cit. I, p. 235 
3 Loc. cit. 2, p. 32. 
4 Loc. cit., p. 347. 
