448 E. C. MacDowell. 
Beddard says that this muscle was lacking in his chimpanzee, or 
else the division of the extensor communis to the fifth digit was 
lacking (which seems more reasonable, since he describes a ten- 
don to the fifth digit that passed through a special compartment 
in the ligament). As will be seen later, the division for the fifth 
digit of the communis is present in my chimpanzee, as well as this 
special extensor. Champneys found the fifth digit of the right 
hand of his chimpanzee supplied only by a slip from the tendon 
of the communis. The left hand wasasin man. Vrolik describes 
the special extensor as the only tendon to the fifth digit, but Mich- 
aélis claims that this is the ulnar belly of the extensor digi- 
torum communis that has become entirely separated. 
The Hatensor digitorum communis in the chimpanzee is separated 
into four bellies half way down the arm. It arises by a strong 
tendinous sheath from the external condyle, from the intermus- 
cular septa between it and the extensor carpi ulnaris, from the 
ulna, radius, and the interosseous septum. In the left hand, two 
divisions of this muscle send tendons to the fourth digit. The 
more radial and stronger arises from the condyle and is joined: to 
the tendon of the third digit by a short tendinous fasciculus. The 
other division arises from the whole length of the ulna. A slender 
fasciculus arises from the ulnar border of this division 1.5 em. 
from the annular ligament. It is provided with a thread-like 
tendon which divides 5 cm. from the ligament. The radial half 
re-divides close to the metacarpo-phalangeal articulation, and 
sends one branch to the tendon for the fourth digit, while the other 
rejoins the ulnar half of the tendon from the first division, which 
is inserted along with the extensor digiti quinti proprius. This 
slip represents the division of the communis for the fifth digit. In 
the right hand, there are three separate tendons for the fourth 
digit, besides the connection with the fasciculus for the fifth digic. 
Vrolik and Macalister found no tendon for the fifth digit in their 
chimpanzees. Primrose describes a slip in his orang that corre- 
sponds to the one just described, but calls it the extensor digiti 
quinti proprius (extensor minimi digiti). In man, the tendon for 
the fifth digit is often absent or rudimentary. . 
The Hatensor indicts proprius arises in the chimpanzee from the 
