Since the observations of Toldt,[4] and more recently of Ranke,[5] on the development of the parietal bone in the human embryo, it appears, though it cannot as yet be said whether the fact is or is not general, that the bone originates from two centres of ossification. These centres appear in most cases one directly above the other, but, as Ranke himself shows,[6] and as can hardly be otherwise, these primitive components of the parietal do not always show the same relations in size or position. The centres blend together, ordinarily, at the end of the third or during the first half of the fourth month of fœtal life. On this account, the typical, complete, horizontal division of the human parietal bone, when met with at any time after the fourth month of fœtal life, is generally interpreted to-day as a retardation of the union, or a persistence of separation, of the two original segments of the bone. Opinion, however, is still unsettled as to the significance of the more atypical, oblique divisions of the parietal, particularly of those where the separation is limited to one angle. Up to the recent contribution on the subject by Ranke, the weight of opinion on the point, although rather briefly expressed, seems to have been in favor of attributing to these smaller, oblique divisions, the same significance as was given to the more typical, horizontal ones. Gruber,[7] in reporting a new case of a bilateral oblique suture in the parietal bone, calls the separated mastoid angles "the secondary posterior parietals." Hyrtl and Welcker advance no definite theories on this point, though the latter expresses an opinion[8] that in both the horizontal division and the separation of the mastoid angle of the parietal bone the development of the condition may be identical. In 1883 Prof. F. W. Putnam, in describing one of his Tennessee skulls with an abnormal oblique suture in each parietal,[9] referred the development of the separated mastoid angle on the right side, as well as the larger oblique inferior portion of the parietal on the left side, to a "separate centre" of ossification. Ranke[10] opposes both Gruber's and Putnam's opinion, and presents instead a theory somewhat vague and not satisfactorily demonstrated, by which he accounts for the origin of oblique sutures from partial horizontal sutures in the parietal bone through "half-pathological processes." In his words, "the oblique parietal suture is allied to the half-pathological conditions of the skull; it is wholly unjustifiable to speak, as W. Gruber has done, of a separate Parietale secundarium posterius, severed by the suture, as of a typical, in a certain sense normal, formation. The oblique parietal suture is nothing more than an incomplete (posterior), true, _i. e._, typical, parietal suture with a sagittal course, modified by certain half-pathological conditions." These half-pathological conditions are produced, the author explains on the preceding page, "durch