434 E. C. MacDowell. 
The Chonro-epitrochlearis is found below the pars costo-ster- 
nalis in the chimpanzee. It arises between the second and fourth 
ribs from the fascia underlying the pars costo-sternalis, 2 em. 
from its origin. It is composed of three strands lying parallel 
to those of the superficial muscle. It is inserted into the humerus 
by a thin strap-shaped tendon, which adheres closely to the ten- 
don of the upper sheet at its insertion into the humerus. 
Bardeen describes the muscle when found in man as follows: 
This is a slip which springs . . . . from the thoraco-abdomi- 
nal fascia beneath the pectoralis major . . . . and extends on 
the inner arm to the intertubercular (bicipital) groove . . . . It 
is found in 12 to 20 per cent of human bodies (Le Double) aud occurs 
normally in many of the lower mammals. 
Duckworth deseribes in a gorilla the separation of the posterior 
fibers of the pectoralis major to form a.separate muscle, the “pec- 
toralis abdominalis,” and identifies it with the chondro-epitro- 
chlearis. However, it seems clear that the pars abdominalis in 
my chimpanzee must correspond to his ‘‘pectoralis abdominalis.”’ 
So, if this slip under question corresponds to any muscle in man, 
it must correspond to the chondro-epitrochlearis. This seems to 
indicate that the abdominal portion of the pectoralis major and 
the chondro-epitrochlearis should not be identified. In man, 
this muscle has been found in one out of eight (Le Double). 
In the baboon, I find a muscle that arises from the rectus 
abdominis and the fascia and cartilage of the seventh rib, below 
the origin of the abdominal portion of the pectoralis major. Its 
fibers form a strip 5 em. wide, which runs parallel to the sternum. 
At the level of the second rib, it becomes cartilaginous, and is 
inserted into the costal cartilage and the surrounding fascia. It 
seems probable that this muscle should be considered a portion 
of the rectus abdominis that has been stranded in the thoracic 
region upon the retreat of this muscle. 
Wiedersheim states that the abdominis in Amphibians extends 
from the tail to the head, and that this muscle crept back with 
the development of the pectorals, which needed a solid frame 
for their insertions. In the lower primates, this muscle regularly 
