No one has ever doubted that man was not identical in structure with the anthropoid apes, or that he differs from them in several characters of the skeleton and of many other organs. The differences, however, do not justify any radical separation of the two. The unusual length of arm, upon which my opponents throw so much weight, is in harmony with the mode of life of apes, as these climb on trees and walk on all four limbs. The difference between apes and Europeans in length of arm is certainly considerable, but is much less in the case of some lower races, such as the Veddahs. In the Akkas of Central Africa, the arms are so long that the hands nearly reach the knees. The fœtus of Europeans also shows an unusual length of arm, probably an ancestral feature. It is only after birth that the arms become relatively shorter. All the other characters different in man and the apes, are equally secondary. On the other hand, just as apes differ amongst themselves, so also, the different races show differences often strongly marked. M. Michaelis,[151] in a comparative study of the muscular systems of monkeys, has made known many details of the musculature in the orang-outan and the chimpanzee, and it appears from his investigations that, although there are some differences between these two apes, they are both closely similar to man. There are many variations in the muscular structure of man, and these find parallels in the muscles of apes. This is also the case with other abnormalities of structure, some of which resemble the condition in mammals much lower than apes. An example of this is the presence of additional pairs of nipples, arranged symmetrically on the sides of the chest and occasionally found in human beings. A similar abnormality has been found in some monkeys, and the best explanation of such an occurrence is that monkeys, like man, are descended from mammals which possessed several pairs of mammary glands.