In interpreting this novel hair stream of man’s chest and neck we are again brought into an atmosphere of struggle of forces. Something has occurred in the course of man’s descent from the ape to interfere very sharply with the course of the hair; and certainly if there be anything in organisms that Heredity, Variation and Selection are unable to do (even when adorned with capital letters, to make them, as Huxley said, “like grenadiers with bearskins,” appear much finer fellows than they are), it is to provide in this reversed stream of hair on man’s chest some cunning “adaptation” to his needs. Selection will not serve; but I think use and habit will. There can be little, if any, doubt that the frequent and active contractions of the platysma muscle in the course of man’s life are the efficient cause of the change of arrangement of hair from a downward simian to an upward human slope. To this opinion the anatomist will promptly reply: “Ah! I have thee there, friend Lamarckian; are there not any number of apes and monkeys that also have an active and efficient platysma?” Undoubtedly there are, and I give here, through the kindness of Professor Keith, a short account of that muscle in simiadæ. It is taken from an unpublished work of his on _The Myology of the Catarrhini--a Study in Evolution_. The account may be only interesting to the professed anatomist, but the conclusions in the summary bear closely on the present problem. I give the exact words from Chapter II., pp. 472, 479. The simian forms examined are _semnopithecus_, _gorilla_, _chimpanzee_, _orang_, _gibbon_, _macacus_, _cercopitheci_, _cynocephali_. “_Summary_: Every gradation is found between the cynocephalic and human forms. The evolution lies in the disappearance of the supra-trapezial origin and the superficial labio-mental insertion. The opposite nuchal and mental angles of a trapezoidal sheet are obliterated and a rhomboidal figure is left. The change may be seen step by step through the _macaci_, _semnopitheci_, _hylobates_, _troglodytes_ and the _orang_ to Man. “The maxillary insertion in man is more extensive than the others, and the insertion is more distinctly demarcated from the quadratus menti origin. But slips between the two muscles are not uncommon. “The sub-mental interdigitation occurs frequently in man, and although its extent varies in the other Catarrhini it is always present. “The upper nuchal fibres, being cut loose in the higher members of the orthorachitial group from their primary origin, became aberrant in their behaviour. Auriculo-labial slips, slips of union with the zygomatici, or simulating a _risorius_, or a relapse to the primitive medial dorsal origin and connection with the occipito-auricular muscles may occur in man as in the others. “Fasciculation of the muscle may occur in man and the _troglodytes_.