Paper - The comparison of auricular height determinations (1925)
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The Comparison of Auricular Height Determinations
By T. Wingate Todd
Hamann Museum, Laboratory of Anatomy, Western Reserve University, Cleveland, Ohio
Ir is self-evident that we must have a determination of cranial height and also that the technique adopted should be applicable to the living head as well as to the skull. For this reason auricular height has tended to displace the basion-bregmatic height. The method of estimating auricular height varies very greatly, so that one hesitates to compare measurements made by one observer with those of another. Some workers indeed discard cranial height altogether, especially upon the living, but this is not the best way to escape from dilemma; rather one should endeavour to learn just how far the measure- ments of different writers may be compared. This latter course is the more necessary since it will be impossible for years to come to persuade all anthro- pologists to use a single method of determination. Records of heads, lacking determination of height, are of greatly restricted usefulness, for length, breadth and height are associated together in compensating balance.
The Frankfort agreement defines the measurement as the distance, from the upper border of the auditory meatus, of the vertex perpendicularly above it and at right angles (1, p. 67) to the Frankfort plane. With existing instru- ments, as Martin points out, this may be difficult (2). Many writers therefore substitute the bregma for the vertical point. The Monaco agreement defines this measurement as the distance of the bregma from the porion-porion line (3). English convention adheres to the Frankfort vertical point but measures the distance from the midpoints of the ear-holes(4). On the cranium the bregma can always be found with sufficient accuracy even when all sutures are syn- ostosed but identification of the bregma on the living is sometimes a matter of great difficulty. Anthropologists of experience usually claim to be able to find it invariably but since anthropological measurements are not always taken by workers of considerable experience it would be well to have a stricter definition of the upper limit of the dimension.
Some years ago the Reserve head-spanner was designed to fill the gap in the anthropologist’s armamentarium. It is really a Gray’s craniometer with the addition of a Frankfort gauge; it has already been described and figured (5, p. 288). The manufacture of this instrument was called for by our own personal needs in this laboratory. We had accustomed ourselves to determining the ear height of crania according to the Frankfort agreement upon acraniostat of Ranke’s pattern (6, p. 838) and it became evident that, with the large amount of material at our disposal, we could not afford to neglect the oppor- tunity of comparing the measurement on the cadaver with that upon the cranium of the same individual after dissection and maceration. In order then that the measurement on both occasions should be the same we built the head-spanner with the Frankfort gauge. It has been tested as to accuracy but we still have to learn how far results obtained by its use may be compared with determinations by other workers who have utilised the bregma as the upper limit of the dimension. To this end I have applied myself in the work reported in this paper.
The problem is the comparison of auriculo-bregmatic height with vertical (or auricular) height upon a significant sample of skulls. Skulls are used in place of heads because there is no question, in them, of the identification of the bregma.
The procedure has been first, the measurement of vertical height above the porion-porion line when the skull is oriented in the Frankfort plane; secondly, the auriculo-bregmatic height; and thirdly the measurement of the chord distance of the vertical point from the bregma. The skull is mounted in the Reserve craniostat and the auricular height determined. Then the skull supports and the horizontal needle (7, p. 148) are swung out of position and the skull rotated so that the vertex scale touches the bregma, the knife edges of the ear rods remaining in contact with each porion. When the bregmatic prominence is diffuse and the two sides of the coronal suture meet the sagittal suture at different points, the bregma is defined as the point at which the line connecting the two parts of the coronal suture cuts the sagittal suture. The vertical point having been marked upon the cranium the distance between it and the bregma is measured with the sliding callipers (Gleitzirkel).
For this purpose I took one hundred male White skulls without regard to age or character of dentition. This is mentioned specifically because age and condition of maxilla do slightly modify the relation of the Frankfort plane to points near the cranial vertex. The modification is so small that it is negligible in this particular investigation and the sample, being unselected in this regard, approximates more closely to samples with which my results must be compared.
Table I shows that in this series of 100 male White skulls the average auriculo-bregmatic height is 115-2 mm. and the auricular height is 115-1 mm. 392 T. Wingate Todd
The probable errors of the means and the variabilities are identical. This very important result justifies us in comparing directly the cranial height in two
Table I. 100 male White skulls
Mean in mm. 8.D. C. of V. Auriculo-bregmatic height 115-2 40-289 4-28 40-204 3-7140-177 Auricular height (OH) 115-1+0-288 4-27 +0-204 3-71+0°177
series when the records of the one series give only auriculo-bregmatic height and the records of the other give only auricular height. For practical purposes it does not matter which method is adopted so long as the sample is one of significant size.
Table II carries the investigation a step further. It shows that, upon the average, the distance of vertical point from bregma is only 11-7 mm. In 92 of our skulls the vertical point lies on the sagittal suture, averaging 12-46 mm.
Table II. Relation of bregma to vertex
Bregma-vertex chord: Mean 11-7 +0-448, S.D. 6-64+0-317, C. of V. 56-75 +.3-464 Number of skulls where bregma lies at vertical point 3
Number of skulls where bregma lies in front of vertex... 92 Number of skulls where bregma lies behind vertex wee
Average bregma-vertex distance: above 92 skulls ... «. 12-46 mm. Average bregma-vertex distance: above 5 skulls ... -. 420mm.
behind the bregma. In five skulls the vertical point lies on the frontal bone, averaging 4-20 mm. in front of the bregma. In only three skulls do bregma and vertex coincide. This deviation of vertex from bregma is much less than the 2-3 cm. ordinarily given as the distance of the vertex behind the bregma. The large variability (56-75 per cent.) indicates however the considerable range in position of vertical point. If we assume that merely stragglers will show a deviation from the bregma of more than three times the standard deviation, we still have a range of nearly 20 mm. in each direction. Hence the range for practical purposes is from about 10 mm. in front of the bregma to rather more than 30 mm. behind the bregma. As the great majority of skulls present a vertex behind the bregma the accepted position of the vertical point is not sufficiently inaccurate to cause any appreciable error. As a matter of fact not one of our series of 100 oversteps these limits.
Table III indicates the effect which is shown in position of the vertical point following infinitesimal alterations in the facial skeleton and Frankfort plane when the dry skull is lying undisturbed on the Museum shelf. I doubt very much if these alterations could be measured directly; they occur in the
Table III. Alteration in position of vertex in approximately one year Skulls completely dried out at commencement of period.
Number of skulls in series wes eee wee ese 57 No movement ... ase eee ose eee eee 47 Movement backwards ... wee wee eee ove 9 Movement forwards... wee wee ae oe 1 Average of 9 above skulls eee +. 194mm.
Forward movement in 1 above skull . ae .. 20mm.
cranial base and the adjacent part of the face but they certainly do appreciably influence the vertical point which lies afar off on the circumference of a circle the radius of which is the auricular height. In the 57 skulls under observation the change takes place in only 10; usually it exhibits its effect in a minute raising of the orbital point of the Frankfort plane with a consequent throwing backwards of the vertex.
The conclusion to be drawn from this work is that we are doing no harm to the cause of physical anthropology in setting forth auricular height on our own large series and in encouraging others to use the head-spanner. On the contrary we are giving confidence in measurement to those who feel diffident concerning their ability always to determine the bregma. In addition we are furthering the prosecution of exact measurement by seeking to substitute a measurement which, with a suitable instrument, can be made definite, for one (auriculo-bregmatic height) which depends largely upon “anatomical appreciation.”” Macdonell was right in insisting that he must have a fixed point for measurements of height but he was altogether wrong in assuming that the bregma, which he could see, is more definitely a fixed point than the vertex which he could not see (8, pp. 835-6).
- For practical purposes it is immaterial whether one use the bregma or the vertical point in measurements of auricular height, provided the sample taken be of significant size.
- The vertical point has the advantage that it bears a definite relation to the Frankfort plane. Since it is determined automatically by the employ- ment of a suitable instrument it has an advantage over the bregma which, in the living, can be estimated only by anatomical appreciation.
- The average distance between the bregma and the vertical point in male White skulls is 11-7 mm. but the variability of this deviation indicates that the vertical point may be found anywhere from 10 mm. in front of the bregma to 30 mm. behind the bregma. In the great majority of crania it lies behind the bregma.
- There may be a small divergence from time to time in the exact position of the vertex on dried skulls following minute adjustments in the cranio-facial skeleton.
(1) Garson, J. G. (1885), “The Frankfort craniometric agreement with critical remarks thereon.” Journ. Anthropol. Inst. vol. xIv, pp. 64-83.
- (2) Marrm, R. (1914). Lehrbuch der Anthropologie. Jena. 8. 529.
(3) Hrpuiéxa, A. (1920). Anthropometry. Philadelphia. p. 15.
(4) “Report of Brit. Ass. Com. on Anthropometric Investigation, 1909.” (Roy. Anthropol. Inst. pubs.), p. 8. (Reprint from Brit. Ass. Rep. 1908, pp. 351 ff.)
(5) Topp, -. W. and Kurnzex, W. (1924). “The thickness of the scalp.” Journ. Anat. vol. LVmI,
(6) Popp, T. W. (1923). “The effect of maceration and drying upon the linear dimensions of the green skull.”” Journ. Anat. vol. Lv, pp. 336-356.
— (1923). “Cranial capacity and linear dimensions in White and Negro.” Am. J. Phys. Anthrop. vol. v1, pp. 97-194.
(8) Pzarson, K. and Davis, A. G. (1924). ‘On the biometric constants of the human skull.” Biometrika, vol. xvi, pp. 328-363. .
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