In discussing such a striking little fact as the one in question, an illustration may serve as an introduction. From the glaciers of Mont St. Gothard two great rivers take their rise. The eastern side of its slopes gives rise to the Rhine, which flows in a northerly direction to the Lake of Constance, the western to the Rhone, whence it pursues a south-westerly course to the Lake of Geneva. No geographer would doubt that certain physical features of the country were to be sought in accounting for the contrary courses of two rivers arising from a comparatively small region, and he finds it by a simple study of the topography concerned. By similar methods we must ascertain why from our little Mont St. Gothard at the level of the second rib, two streams of hair separate and pursue nearly opposite directions. A little knowledge of the superficial anatomy of the chest and neck throws some light at once on the problem. It so happens that if one made a simple map of these hair streams, and at the side of it a drawing of the platysma myoides muscle, it could not fail to strike one that the correspondence of the surfaces occupied by the two phenomena was very significant. It is going too far to say that the correspondence is complete, but it is so nearly so that one may fairly say that the reversed stream of hair which begins at the second rib and goes up the neck, lies over the platysma muscle. The stream of hair does not extend up to the lower part of the face and lower jaw, it does not cover the outlying portion of the platysma on the side of the neck and it begins on the chest a little above the rather uncertain origin of the platysma fibres from the fascia of the chest. But the correspondence of its surface with the main part, or about five-sixths of the platysma, is most suggestive. This muscle is one of the subdermal sheets that are found in many mammals, and though it is not a continuation or descendant of the fly-shaker or panniculus carnosus, which is often referred to in these pages, it is an analogous feature of man. It is _closely attached_ at its lower part to the skin over it and more loosely at its upper. It has various functions attributed to it, as I will mention later; but there is one effect of its action which is very evident in a thin person, that is to say, it wrinkles the skin over it in a vertical direction. This it does, whatever else it may do. Struggles of the Platysma.