26 
PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
extended up to the greater tuberosity of the humerus and the capsule 
of the joint — the insertion extended further up on the humerus than the 
other two portions of the muscle. (2) Pars sterno-co stalls (plate IV, 
fig. 2 ,p.m. 2), arose from the cartilages of the third, fourth, fifth and sixth 
ribs, and from the adjacent portion of the anterior aspect of the sternum. 
It was inserted by means of the strong fascia over the biceps tendon into 
the humerus. The fibres of this portion of the muscle passed almost 
horizontally from origin to insertion. It lay intermediate in position 
between the pars costo-abdominalis and the pars sternalis. (3) The 
Pars sternalis (plate IV, fig. 2 ,p.m. j), arose from the anterior surface of 
the manubrium sterni near its upper margin. There was no attachment to 
the clavicle. The fibres passed very obliquely from above downwards 
and outwards in front of the other portions of the muscle. The muscle 
was inserted into the humerus on the anterior aspect of the bone in 
front of the biceps by an insertion 2 cm. wide, extending further 
down on the bone than the other portions of the muscle. The three 
portions of the pectoralis major were very definitely separated from 
one another, the intervals being filled in by a large amount of fat. 
The other three anthropoid apes, according to Bischoff, possess a 
fourth division of the pectoralis major, viz., a “ pars clavicularis ” arising 
from the sternal end of the clavicle, whilst in an Orang dissected by 
Bischoff^ the clavicular portion was, as in my specimen, absent. On 
the other hand Fick^ describes a clavicular portion in both Orangs 
dissected by him, and Bischoff^ found in a second Orang examined by 
him, a portion of the pectoralis major arising from the ligaments of the 
sterno-clavicular joint. Chapman and Owen both failed to find a 
clavicular portion in the Orang. Bischoff, it may be added, is authority 
for the statement that the pars clavicularis fails in the lower apes. 
It would therefore appear that the pectoralis major muscle is com- 
posed of four portions ; this fact is recognized by Testut in describing 
the muscle in man as consisting of : ist, portion claviculaire ; 2nd, por- 
tion sternale ; 3rd, portion abdominale ; 4th, portion chondro-costale. 
The clavicular portion, which is, as a rule, well developed in man, is 
1 Loc. cit., I, p, 208. 
2 Loc. cit., I, p. 15 and 2 p. 298. 
3 Bischoff, “ Beitragre zur Anatomic des Gorilla,” Abhand. der math.-physik. Classe der konig^. 
bayer. Akad. der Wissenschaften, Vol. XIII, Abth. 3. Munchen, 1880, p. 9. 
4 Loc. cit., p. i6i. 
5 Loc. cit., p. 29. 
6 Loc. cit., Vol. I, pt. 2, p. 722. 
