PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
27 
present only occasionally in the Orang, and is absent in the lower apes. 
On the other hand, the Gorilla, Chimpanzee, and Gibbon resemble man 
in the well-developed clavicular portion of this muscle ; in the Gorilla, 
in fact it is more strikingly developed than in man. One notices in 
man considerable variation in the width of the interval separating the 
clavicular portion of the muscle from the remaining part ; according to 
Testut this may be several centimetres. One is inclined to believe that 
the portion in the Orang which I have described as the “ pars stern- 
alis ” in reality corresponds to the “ pars clavicularis” of man (see plate 
IV, Fig 2,/.M. j). My reason for coming to this conclusion is that we 
have in the anterior part of the “ pars sterno-costalis ” in my Orang a 
portion corresponding to the “ pars sternalis ” of man, whilst the wide 
interval existing in my Orang between the middle and upper portions 
of the muscle would correspond to the varying interval observed in man 
between the sternal and clavicular portions of the muscle. It would 
appear, therefore, that the upper portion of the great pectoral has gra- 
dually extended its width of attachment, and has also travelled out. 
wards. At first purely sternal (as in the lower apes) then having a 
varying degree of clavicular attachment, In the case of Bischoffs 
Orang, quoted above, the attachment was intermediate in position, 
namely to the sterno-clavicular joint. One may note that in man the 
muscle may extend along the clavicle and become incorporated with 
the deltoid or, on the other hand, in rare cases, the clavicular portion 
may be absent (Quain). In my Orang a large triangular interval 
existed between the anterior border of the deltoid and the superior 
border of the pectoralis major and the clavicle ; this space was crossed 
by the pectoralis minor. 
In connection with the pectoralis major in man, various anomalous 
muscles have been described. In a female subject Bryce^ has recently 
reported the following anomalous development of the pectoral sheet. 
The upper part of the pectoralis major muscle was ill-developed, being 
represented by a narrow band resembling in fact, very much, the pars 
sternalis which I have described in my Orang. He found present also 
a “ sterno-clavicularis ” which arose from the side of the manubrium 
sterni and the second costal cartilage, and was inserted into the clavicle 
along the inner two-thirds of the bone. A “sternalis” attached partly to 
the second cartilage and the tendon of the sterno-clavicularis above, and 
below to the aponeurosis of the external oblique opposite the seventh 
cartilage, and a “chondro-epitrochlearis ” which arose from the outer end 
I T. H. Bryce, “Note on a Group of Varieties of the Pectoral Sheet of Muscle.” Journ. of Anat. 
and Phys., Vol. XXXIV, 1899, P- 7 S- 
