Geo. S. Huntington — 163 
portion of the deeper layer (Pectoralis minor) to come to the surface as 
the thin abdominal sheet. The latter, in the superficial dissection (PI. 
III, Fig. 3 right side), appears to continue the layer of the Pectoralis 
major caudad beyond the sternum. But after reflection of the divided 
Pectoralis major it is seen that the abdominal portion is really directly 
continuous with the deeper sternal division of the muscular mass (Pec- 
toralis minor), the entire sheet having a common humeral insertion 
under cover of the superficial layers of the Pectoralis major into the 
lateral surface of the shaft of the humerus. ; 
The Pectoralis mass has no attachment to the clavicle. The clavi- 
cular portion of the Deltoid, extending mesad to the sterno-cleido-mastoid 
muscle, is separated from the cephalic border of the Pectoral by a cleft 
filled with loose cellular connective tissue. 
In none of the Marmosets examined was a distinct axillary arch en- 
countered. ‘The panniculus in these animals appears very slightly devel- 
oped in the thoraco-humeral segment, and not recognizable as a distinct 
layer. 
2nd Example: Nycticebus tardigradus, The Slow Lemur, Columbia 
University Museum, No. 1068 (Pl. III, Fig. 4). Compared with 
Hapale the Pectoral muscle of this lemur presents : 
1. A less complete differentiation of ecto- and ento-pectoral layers. 
2. A greater independent pannicular development and, as a segment 
of this sheet, a distinct axillary arch. 
3. A marked reduction of the abdominal portion of the Pectoralis. 
The Pectoralis arises from the entire extent of the ventral midline 
of the sternum, passing at the caudal extremity of the bone laterad 
to the eighth costal cartilage, and by a thin aponeurotic lamella to the 
ninth costal cartilage. ‘The converging fibres of the superficial portion 
of the muscle form a triangular sheet which is inserted into the lateral 
surface of the shaft of the humerus, closely united with the adjacent 
margin of the Deltoid. The latter muscle, in its ventral segment, arises 
from the outer third of the ventral surface of the clavicle, leaving a 
broad triangular interval between its ventral margin and the cephalic 
border of the Pectoralis, in which the broad and well-developed Sub- 
clavius appears after removal of the superficial fatty and connective 
tissue filling in the fossa. 
Division of the superficial layer of the Pectoralis (Pl. III, Fig. 4, left 
side) reveals the existence of a deeper, entopectoral layer, separated from 
the ectopectoral layer in the cephalic and middle portions, but directly 
continuous with and inseparable from it at the caudal extremity of the 
entire Pectoral mass. This rudimentary representative of the human 
