1909-10.] Short Muscles of the Hand of the Agile Gibbon. 205 
muscle of this digit ; the inner or fourth contrahens is also largely blended 
with its fibres. 
We now come to the description of muscles lying deeper in the palm of 
the hand. In describing them it is well to keep before one’s mind the three 
layers of muscles of the typical manus — the contrahentes, the palmar, and 
the dorsal interossei muscles ; or, according to the better anatomical nomen- 
clature of Professor Cunningham, the adductores, the flexores breves, and 
the abductores. 
There are in the hand of the gibbon certain muscles which do not at 
first sight fall into any of these three layers. These muscles I have termed 
musculi accessorii interossei. 
The morphological position of these as well as of the other muscles will 
be dealt with after a description of each has been given. 
First Layer : Contrahentes or Adductores. 
All four of these muscles are present, the largest being that of the thumb, 
which shows a segmentation into an adductor transversus and an adductor 
obliquus pollicis. They all take origin from the central portion of the 
palm in the neighbourhood of the 3rd metacarpal bone, and from a well- 
marked tendinous fascia which occupies the hollow of the hand and is best 
marked over the 3rd and 4th metacarpals. 
Contrahens 1. 
This muscle is segmented into two parts, an adductor transversus and 
an adductor obliquus pollicis. 
ADDUCTOR TRANSVERSUS POLLICIS. 
Origin . — From the front of the anterior annular ligament, and from the 
front of the bases of the 2nd and 3rd metacarpals. 
Insertion . — Into the inner side of the distal half of the 1st metacarpal 
bone, slightly in front of the insertion of the obliquus. 
Structure . — The muscle is fleshy throughout its entire extent. It is 
fan-shaped, being widest at its base. 
ADDUCTOR OBLIQUUS POLLICIS. 
Origin . — From the front of the proximal half of the 3rd metacarpal, 
and from the layer of fascia over the metacarpals. 
Insertion . — Into the inner side of the distal half of the 1st metacarpal 
rather behind the attachment of the last muscle, and into the inner side of 
the proximal phalanx of the 1st digit. 
