770 Muscular Variations 
11. There is no clavicular portion of the Pectoralis major—a corre- 
sponding mesal development of the clavo-humeral Deltoid occupying 
the situation of the human clavicular portion in Hapale while in Nyc- 
ticebus the Delto-pectoral interval develops into an extensive subclavi- 
cular fossa. 
II. Lower Monkeys.—1. The same general arrangement of the ecto- 
pectoral layer, with a distinct sternal Pectoralis major is observed. 
2. In the entopectoral plane the Pectoralis minor has differentiated 
completely from both Subclavius and abdominal pectoral. 
3. The Pectoralis minor is still almost entirely sternal in origin, but 
migration laterad to the costal cartilages has begun in the cephalic 
segment of the muscle. 
4. The insertion of both ecto- and entopectoral planes corresponds 
still to the earlier type but has moved further cephalad upon the humerus 
to the lateral tuberosity. 
5. The axillary arch is relatively reduced and indirectly connected 
with the Latissimus. 
6. There is no clavicular portion of the Pectoralis major. 
7. More extensive migration of the Pectoralis minor origin, both 
cephalad and laterad from sternum to costal cartilages, is observed in 
some forms transitional between the intermediate and secondary types 
of the muscle. 
III. Man and the Anthropoid Apes.—1. Complete differentiation of 
Pectoralis major and minor. 
2. Migration laterad of origin of latter muscle from sternum to ribs. 
3. Lateral extension in deeper parts of origin of Pectoralis major to 
costal cartilages. 
4. Migration cephalad of insertion of Pectoralis minor from lateral 
tubercle of humerus to coracoid process of scapula. 
5. Reduction of Pectoralis abdominalis and secondary addition of 
same to Pectoralis major, joining the deep layer of the tendon of inser- 
tion as the “ abdominal slip.” 
6. Development of eclavicular portion of the Pectoralis major, and 
corresponding reduction of the clavo-humeral Deltoid. The secondary 
character of this addition to the primitive sternal Pectoral in man is 
still attested by— 
(a) Cellular interval between it and sterno-costal division. 
(b) Variations in the nerve supply (ant. thoracic, circumflex). 
(c) Range of independent physiological action of the two portions. 
7. Default of axillary arch, the last remnant of the thoraco-humeral 
