The disproportion of growth of the two original segments of the parietal bone will, I believe, be found more common as attention is directed to this subject. It can be well explained, though there may at times be other factors present, by a difference in the blood-supply to the two centres. This of course may occur not only in different skulls, but also on the two sides of the same cranium.
Footnotes
[1] Die überzähligen Hautknochen des menschlichen Schädeldachs, Abh. d. k. bayer. Akad. d. Wiss., II Cl., XX Bd., II Abth., pp. 36 et seq., Fig. 17.
[2] L. c., p. 41. Among 3000 Bavarian crania, Ranke found but one with complete and three with incomplete parietal sutures; basing his conclusion on this observation, he says, "Bei den Orangutanschädeln ist die Häufigkeit der Scheitelbeinnäthe circa 40 mal grösser als bei dem erwachsenen Menschen."
[3] Since finding the abnormal sutures on this skull, I have been able to present the same at a meeting of the Association of American Anatomists (1899) and before the Ethnological Society of New York City (1900).
[4] Toldt, C., in Maska's Hdb. d. gerichtl. Med., 1882, v. III, p. 515; the same in his U. d. Entwick. d. Scheitelbeins d. Menschen, Zeitschr. f. Heilkunde, 1883, v. IV, pp. 83–86.
[5] L. c., pp. 324–330.
[6] L. c., pp. 327–330, Figs. 29–32.
[7] Gruber, W., Beobacht. a. d. menschl. u. vergl. Anat., Berlin, 1879, II Heft, pp. 12–15.