8o 
PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
complete adducting apparatus (e.g., Cynocephalus) but also in those in 
which it is only represented by the adductors of the hallux and by 
fibrous bands {eg, Orang) and in those in which it is reduced to the 
adductors of the great toe only {e.g. Gorilla). 
3. Ruge has pointed out that the deep division of the external plantar 
nerve, as it runs inwards across the sole is placed between the adductor 
muscles and the other muscles of the intrinsic group. This is a most 
useful, and, as a general rule, a most reliable guide in determining the 
muscles which belong to the plantar layer. Ruge^ points out that in 
mammals the deep division of the external plantar passes inwards 
between the interossei and the contrahentes (adductors). In man this 
nerve passes between the plantar interossei beneath and the adductor 
obliquus hallucis above, and this Cunningham looks upon as most 
suggestive. 
4. In a foot dissected by Cunningham he found a distinct fleshy slip 
proceeding from the outer edge of the adductor obliquus hallucis to be 
inserted into the outer side of the base of the first phalanx of the index. 
This clearly represented the adductor indicis. 
Cunningham would therefore place in the intermediate layer the 
following muscles : 
1. Flexor brevis pollicis, deep and superficial heads. 
2. Flexor brevis minimi digiti. 
3. Plantar interossei. 
In studying the interossei group (palmar and dorsal), as found in my 
Orang, and figured in Plate V, it appears to be a question worth con- 
sidering as to the relation of the palmar portion of the dorsal interossei 
to the intermediate layer. On reference to the dissection (as figured in 
plate V), one cannot but be struck by the symmetrical arrangement of 
the palmar interossei and the palmar portion of the dorsal interossei 
as forming one group of flexores breves, and the origin of the palmar 
interossei may yet be accounted for by subdivision of originally single 
muscles, or we may suppose that fusion has occurred to produce the 
connection of the palmar portion with the remaining part of the dorsal 
interossei. In other words one would venture to suggest that the 
intermediate layer is represented in the Orang by the palmar interossei 
I G. Rug-e, “ Zur vergleichenden Anatomie der tiefen Muskeln in der Fusssole.” Morphologrlsches 
Jahrbuch, Vol. IV, 1878, p. 644. 
