96 Darwin, and after Darwin. 
On the other hand, however, there is reason to doubt 
whether this form of tibia in man is really a survival 
from his quadrumanous ancestry. For, as Boyd- 
Dawkins and Hartmann have pointed out, the degree 
of flattening presented by some of these ancient 
human bones is greazer than that which occurs in any 
existing species of anthropoid ape. Of course the 
possibility remains that the unknown species of ape 
from which man descended may have had its tibia 
more flattened than is now observable in any of the 
existing species. Nevertheless, as some doubt attaches 
to this particular case, I do not press it—and, indeed, 
only mention it at all in order that the doubt may be 
expressed. 
Similarly, I will conclude by remarking that several 
other instances of the survival of vestigial structures 
in man have been alleged, which are of a still more 
doubtful character. Of such, for example, are the 
supposed absence of the genial tubercle in the case 
of a very ancient jaw-bone of man, and the disposition 
of valves in human veins. From the former it was 
argued that the possessor of this very ancient jaw-bone 
was probably speechless, inasmuch as the tubercle in 
existing man gives attachment to muscles of the 
tongue. From the latter it has been argued that all 
the valves in the veins of the human body have 
reference, in their disposition, to the incidence of blood- 
pressure when the attitude of the body is horizontal, 
or quadrupedal. Now, the former case has already 
broken down, and I find that the latter does not hold. 
But we can well afford to lose such doubtful and 
spurious cases, in view of all the foregoing unquestion- 
able and genuine cases of vestigial structures which are 
