The Myology of Chimpanzee and Baboon. 449 
distal four-fifths of the ulna. It is divided into three parts which 
give off three tendons. Two of these are large and are inserted 
into the extensor expansion over the dorsal aspect of the proximal 
phalanges of the second and third digits respectively, on the ulnar 
side. ‘The third tendon is very small and is closely applied to 
the tendon for the second digit, from which it becomes separated 
1.5 cm. before its insertion into the radial side of the extensor 
expansion of theindex. Similar conditionsare found in the baboon. 
Beddard describes this muscle in a chimpanzee as having but 
one strong tendon and that joining the branch of the communis 
for that digit. Mayer found it small or entirely lacking in the 
chimpanzee and in the orang. In the chimpanzees of Hartmann 
and Macalister, an extra tendon for the third digit was found. 
Champneys found such a condition in his Cynocephalus and 
Le Double reports its occurrence in man. Duckworth describes 
the double extensors to all the fingers (formed by branches of 
the indicis proprius and digiti quinti proprius to the third and 
fourth digits respectively) as being constant in many apes. 
Again, Primrose quotes Huxley as stating that there were origi- 
nally two sets of extensors, just as there were two sets of flexors, 
and that this is indicated by the dividing of the special extensors 
of the second and fifth digits. It may be remembered that. I do 
not find a division of the tendon of the extensor digiti quinti 
proprius, but I do find a division in the tendon of the fasciculus 
of the communis for the fifth digit which could not correspond to 
a deep flexor, as it was joined directly to the tendon of the com- 
munis. 
II. MUSCULATURE OF THE LOWER EXTREMITY 
A. Muscies or THE Hip 
The Scansorius is present in the chimpanzee. It arises from the 
anterior border of the ilium below the anterior superior spine, 
and its insertion is into the anterior border of the great trochanter, 
together with the gluteus minimus. These two muscles are inde- 
pendent for two thirds of the way from their origins. 
In his chimpanzee, Beddard found the scansorius well devel- 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 10, No, 3. 
