78 
PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
Outer head supplied by the deep branch of ulnar alone 5 cases. 
“ “ “ twigs from ulnar and median 19 “ 
“ “ “ median, inner by the ulnar 5 “ 
Median nerve, giving twigs to both heads, inner head also receiving an 
ulnar supply 2 “ 
In a careful study of the muscles of the feet of certain of the mar- 
supials, Cunningham demonstrates three layers, and concludes that this 
trilaminar arrangement is the typical one for the intrinsic muscles of 
the foot and the hand. 
1. A layer of adductores. 
2. An intermediate layer of flexores breves. 
3. A dorsal layer of abductores. 
Young^ has also investigated the intrinsic muscles in the foot and 
hand of marsupials and agrees with Cunningham in his observations on 
the trilaminar arrangement ; he extended his observations to other 
members of the group than those dissected by Cunningham. 
Cunningham explains that deviation from this trilaminar arrange- 
ment may occur by subdivision, fusion or suppression of members of 
one or other of the layers. The suppression may be complete or partial 
and the muscle may be represented by ligaments. 
In transferring our attention to the conditions obtaining in the ape 
we can readily determine the trilaminar arrangement and we observe 
that either the muscle group in the hand or that in the foot corresponds 
to this typical arrangement. Thus by reference to Plate 3 one can 
readily distinguish the three layers in the hand of my Orang. 
1. Fig. 5 shows the muscles of the palmar layer composed of the 
adductor muscles of the thumb. 
2. Fig. 6 demonstrates certain of the flexores breves of the inter- 
mediate layer. 
3. Fig. 7 shows the dorsal layer of the abductores. 
As I have already stated, so far as the so-called ‘‘ interossei ” are con- 
cerned, the condition found in the foot of my Orang corresponded to 
that found in the hand in every particular, and in plate V is illustrated the 
arrangement of these muscles in either foot or hand. 
I A. H. Young-, “The Intrinsic Muscles of the Marsupial Hand.’’ Journ. of Anat. and Phys. 
Vol. XIV, 1879, p. 149. 
