Inion決定に就いて

§Preface: The Inion is one of the most important points in the craniology. But the way of its settling is not yet fixed. Some authors settle it on the surface and even on fairly upper part of the external occipital protuberance, and some others, below the protuberance and still others, on the apex of it. The way of settling this important point is not fixed because the difinition of the inion has not been setlled, and is due to the ignorance of anatomical relations of things in this part. Oppenheim proposed in his “Ein Beitrag zur exakten Bestimmung des Inion” (Arch. Anthr., 1910), to settle the inoin “auf der Mitte des Tuberculum linearum bzw. auf eine an der Stelle derselben auftretender Rauigkeit bzw. auf die Vereinigung der Protuberantia occipitalis externa mit dem Tuberculum linearum” This proposal seems to have no meaning. First, what is meant by “Mitte des Tuberculum linearum” ? Second, “die Vereinigung der Protuberantia occipitalis externa mit dem Tuberculum linearum” is very rarely seen. Moreover, this definition cannot decide a definite point as Inion. Martin agreed with Oppenheim and followed him in his “Lehrbuch der Anthropologie, 1928” and added that the situation of internel occipital protuberance is not to be regarded in settling the inion. I cannot agree with Martin, and find no reasod why the internal occipital protuberance must not be regarded in settling the inion. I believe that the inion must be defined and determined only in its relation to the endinion. The reasons are: first, the inion devides the calvarium from basis cranii ; second, the ratio between the calvarium and basis cranii suggests the ratio of development of great brain to other parts of brain ; third, the endinion is the deviding mark of cerebral and cerebellar parts on the interior surface of the skull. §Method of study: -From these points of view, I examined several points above and bellow the protuberance, regarding their relations to the endinion. Each occipital bone examined was sawed off in median-sagittal plane, namely in the plane which passes through approximately the following three points, o (opisthion), tl (the gravity centre of Tuberculum linearum) and pt (the lowest point of outer border of external occipital protuberance), perpendicularly to the surface of the bone, paying attention to the protuberance or the tuberculum linearum and opisthion. Putting it on a paper, the out line of this disected 'plane is drawn as carfully as possible, and the points o, pt, lns and tl are marked on it (cf. Fig. 1). The point tc is endinion, the point where the connecting line of both sides middle line of sulcus transversus is cut by the median-sagittal plane; the lns is the point where the tanget of the linea nuchae suprema on both sides is cut by the median-sagittal plane. If these points are not found on the median-sagittal plane, perpendicular lines are drawn from these points to the plane, and their feet are marked on the bone and the picture. Moreover, on the picture are drawn lines from o to both pt and tc, and to these are drawn perpendicular lines from these points tc, pt lns and tl. On each line (or plane) o-tc and o-pt the distances from tc to the feet of other three points were measured in mm. and treated statistically. If the feet of the perpendicular lines fall above the tc, they are desighnated as +, if below, as -. § Results of study: -The results are shown in Table 1 Amoung them, the underlined are omitted from the statstical calculation, as they are very rare ones. (risk of error is lower than 5%). First, I thought that there are some differences according to the differences of appearance of bone surface and classified all material into 5 groups. Group I includes the cases having the torus occipitalis transversus. Group II ; the protuberance is prominent and protruded or elongated downwards. Group III ; the linea nuchae suprema is clearly developed.