432 E. C. MacDowell. 
directly into the lip of the bicipital groove of the humerus, from 
the tendon of the pars abdominalis to the insertion of the deltoid- 
eus. The third division (c) which is, nearly as well developed 
as b, arises from the mesial two-thirds of the clavicle. It is 
inserted into the humerus for 5 em. below its head, and overlaps 
the insertion of the second division (b). But slight differentia- 
tion is found between the main masses of the second and third 
divisions. There is an indication of a separation of a bundle of 
fibers anteriorly, which may represent a pars sternalis, but this 
bundle has no distinct insertion. 
In the baboon, the pars clavicularis, is very poorly developed. 
The pars abdominalis (fig. 1, 4) is a distinct ribbon-like band, 
which arises from an aponeurosis with the external oblique 5 cm. 
from the sternum, and extends from the seventh to the ninth rib. 
In the axilla, it is entirely covered by other muscles. It is inserted 
without a tendon, into the humerus close to its head. The pars 
costo-sternalis (fig. 1, P) is highly developed. It arises and is 
inserted asinman. The parssternalis is very closely intermingled 
both with the deltoideus and the main portion of the pectoralis 
major. It arises from the sternum (afew fibers are supplied from 
the proximal end of the clavicle) and is inserted into the humerus, 
proximal to the insertion of the pars costo-sternalis. 
This condition bears out Bischoff’s statement, quoted by Prim- 
rose, that the pars clavicularis is wanting inthelower apes. Hunt- 
ington and Michaélis do not find it in Cynocephalus. Primrose 
considers that the attachment of the great pectoral has slowly 
crept out from the purely sternal origin, shown in the lower apes, 
to the origin which extends nearly two-thirds the way along the 
clavicle and joins the deltoideus as it does in my chimpanzee. 
Champneys found that the pectoralis major in his chimpanzee 
arose from eight ribs. The three divisions were not apparent, 
although two slips were differentiated. These arose from the 
fourth and fifth ribs respectively, and were fused with the main 
part of the muscle at the level of the lower border of the axilla. 
He describes the clavicular origin in the baboon as extending 
one-eighth of the way from the sternal end of the clavicle. Vro- 
lik describes this muscle in his chimpanzee as having a clavicular 
