1 6 PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
Clearly the oblique grooves in man indicate that the fingers are not 
bent in a perfectly straight direction into the palm, but are directed 
somewhat obliquely towards the thumb, hence the line associated with 
that movement of flexion is oblique, in other words it is at right angles 
to the line of movement — the fingers are opposed to the thumb. In the 
Orang, on the other hand, the fingers are flexed directly into the palm, 
and the animal is thus better able to grasp a cylindrical object, such as 
the branch of a tree, whilst it is not so well adapted to grasp a sphere, 
as the hand of man. The development of the ball of the thumb in man 
is due to the presence of a well-developed group of muscles which have 
to do with adduction and opposition of the thumb. These muscles are 
by no means so well developed in the hand of the Orang. It must be 
noted, however, that the groove of opposition is present in the Orang, 
and that the feeble thumb can be opposed. In the Orang, too, there is 
a marking off of the ball of the little finger ; this is sometimes, but not 
always, present in the hand of man. 
One would readily suppose that the lines in the palm of the hand were 
produced after birth when the muscles of the hand had brought about the 
various movements, but such is not the case. Professor Sir William 
Turner^ makes an interesting observation regarding this when he says : 
“These grooves are present in the infant’s hands at the time of birth ; and 
I have seen them in an embryo, the spine and head of which were not more 
than 90 mm. (three and a-half inches) long. They appear in the palm 
months before the infant can put its hand to any use ; though it is pos- 
sible that the muscles of the thumb and fingers do, even in the embryo, 
exercise some degree of action, especially in the direction of flexion. 
These grooves are not, therefore, acquired after birth. It is a question 
how far the intra-uterine purposeless movements of the digits are suffi- 
cient to produce them ; but even, should this be the case, it is clear that 
they are to be regarded as hereditary characters transmitted from one 
generation of human beings to another. They are correlated with the 
movements of the digits, which give the functional power and range of 
movement to the hand of man.” 
It may be remarked here that the grooves on the palm differ some- 
what in the different anthropoid apes ; thus Hepburn^ shows that the 
lines across the palm in the Gorilla are decidedly oblique, and the hand 
1 W. Turner, “ Some Distinctive Characters of Human Structure,” Report of the British Association 
for the Advancement of Science, 1897, p. 768. 
2 David Hepburn, “The Integfumentary Grooves on the Palm ot the Hand and the Sole of the Foot 
of Man and the Anthropoid Apes,” Journ. of Anat. and Phys., Vol. XXVH, 1892-93, p. 112. 
