Geo. S. Huntington 169 
connection with the tendon of insertion of that portion of the deeper 
plane, which in Cynocephalus has differentiated distinctly as the Pecto- 
ralis minor. 
From this hypothetical common ancestral type of the Primate Pectoral 
gronp the further evolution along the lines illustrated by the represen- 
tative examples above indicated may be summed up in the following 
manner : 
I. Lemurs and Marmosets.—1. The influence of the sternum, as 
affording a fixed line of origin, determines the differentiation of the 
main ectopectoral layer as Pectoralis major. 
2. The same influence extends to the deeper plane of the Pectoral 
mass in the sternal region and leads to the beginning differentiation of 
the Pectoralis minor, which muscle is, however, still entirely sternal 
in origin. 
3. Pectoralis major and the segment of the deeper plane corresponding 
to Pectoralis minor have completely differentiated from each other in 
the Marmosets, while in Nycticebus the caudal portion still forms a 
continuous mass common to both planes at the origin, but differentiated 
toward the insertion. 
4. In I/apale the Pectoralis minor is still nearly directly continuous 
with the Subclavius cephalad, and with the Pectoralis abdominalis 
eaudad. 
5. In the same animal this latter muscle forms an extensive thin 
superficial muscular sheet investing the abdominal region and retaining 
characters pointing to its derivation from the pannicular sheet of the 
trunk. 
6. In Nycticebus the abdominal Pectoralis of Hapale still appears as 
part of the general pannicular plane whose only connection with the 
Pectoral system appears in the well developed axillary arch. 
7. The axillary arch of Nycticebus is still entirely pannicular in 
character and has not contracted the secondary attachment to the axil- 
lary margin of the Latissimus dorsi. In Hapale, as a specific character 
the axillary arch seems to default. 
8. The Pectoralis major is folded at the insertion into the lateral 
humeral ridge and occupies the position which it retains in the more 
completely differentiated higher types. 
9. The continuity of the Pectoralis minor and abdominalis is pre- 
served at the insertion into the lateral and surface of the shaft of the 
humerus under cover of the Pectoralis major and Deltoid. 
10. The caudal margin of this deeper plane of the Pectoral insertion 
receives the insertion of the axillary arch. 
