Paper - Observations on metopism (1917)

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Bryce TH. Observations on metopism. (1917) J Anat. 51(2):153-166. PMID 17103812

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This 1917 paper by Bryce describes abnormal development of the skull associated with metopism. Metopism is a persistent metopic suture, or persistence of the frontal metopic suture in the adult human skull.

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Observations on Metopism

By Professor THomas H. Bryce, University of Glasgow, and MatrHew Youne, M.D., Statistical Department, National Research Laboratory.


The excellent summary given by Le Double? of the statistics of metopism shows that the condition occurs in from 9 per cent. to 10 per cent. of all European crania irrespective of race, of skull form, or of mental condition. Metopism is certainly more frequent in the white races, rarer in the lower races of mankind. It has not so far been observed in the anthropoid apes. More than forty years ago Welcker? furnished statistics which seemed to show that metopism occurred more frequently in brachycephalic than in dolichocephalic races, and the generalisation found some support from the observations of Papillaut.2, Parsons* found a metopic suture persistent in the adult in 52 out of 590 specimens (7.e. 9 per cent. approx.) in the Hythe series of skulls, which are remarkable for their shortness, being practically equal to the South German in that measurement. He states that the number of metopic skulls occurring in the two sexes shows no appreciable difference, although, according to the figures supplied, there would appear to be some relationship between the frequency of the anomaly and age incidence. Under the age of twenty years the frequency was 20°8 per cent. ; in the specimens between twenty and forty it was 9°8 per cent.; and in those over forty, 64 per cent. In Macdonnell’s Whitechapel English series,t dolichocephalic in form, the frequency of the anomaly was 8:2 per cent. Turner in his Challenger Report (part xxiv., 1884) says of his 143 crania of aboriginal races from South Africa, South America, Australia, and the Pacific Islands that “the absence of the metopic condition was remarked in the aboriginal series,” though he had seen it in the skulls of a Veddah and of an Andaman Islander. Flower observed metopism in six Andamanese crania. Statistics furnished by Le Double’s article serve also to prove the greater rarity of the condition in the lower races of mankind.

In the long series of West Scottish skulls preserved in the Anatomy Department of the University of Glasgow, and described recently in a memoir Dr Young published in the Transactions of the Royal Society of Edinburgh’, metopism occurs in 9°5 per cent. of the crania. The series is remarkably uniform in character, dolichocephalic in type, yet the percentage closely approximates to that in the Hythe series. From the series of 75 metopic skulls two groups were selected—consisting of 45 and 20 specimens respectively. The first group was attributed to the male sex, the second to the female, while the remaining specimens have been noted as doubtful. The determination of sex, difficult in all circumstances, is specially difficult and uncertain in the case of metopic skulls, because, as will afterwards appear, the frontal bone has in the majority of cases an upright character. We do not, therefore, lay emphasis on the sex characters, and in consequence the series are named A and B. A is preponderantly male, B preponderantly female.

1 Variations des os du crane de Vhomme, etc., Paris, Vigot Fréres, 1903.

? For references see Le Double.

3 Journ. Roy. Anthropol. Institute, vol. xxxviii., 1908. + Biometrika, vol. iii. p. 1412.

Cranial Measurements

Table I. shows the mean values for the measurements and indices of the cranial box of the metopic skulls in apposition to the mean values for the same measurements shown by the complete male non-metopic series of 405 skulls and the female series of 100.

The comparison is not without interest. Considering the absolute measurements first of all, we observe that, while the mean capacity of the metopic group A is slightly less than that, in the male non-metopic group, the opposite holds for the B series as compared with the female non-metopic.

The mean length in the A metopic group is about 3 mm. less than that shown in the male non-metopic group, while, though the mean length in series B is less than the normal female, there is less than one millimetre of difference in the values.

It is frequently stated that there is an increase in the mean maximum breadth of the metopic skulls in a series over the general value for maximum breadth. In the A series and the non-metopic male group the mean maximum breadths are practically identical, while in the B group the metopic mean is 1:29 mm. in excess of the female non-metopic mean. Parsons found the increase in the Hythe crania to equal about 1:3 mm.

In the Whitechapel series Macdonnell found the mean values identical in the metopic and non-metopic female crania, while in the male series the metopic group had a mean value 1 mm. in excess of that in the nonmetopic group. These data go to show that if there is any increase in maximum breadth in metopic skulls over the normal members of a series it is very slight in degree.

1 Vol. li. part ii. (No. 9).

TABLE I, Male. | Series A. | Female. Series B. Sr. | _ — | _ . Non-metopic | Metopic | Non-metopic | Metopic Character { (405). | (45). «| (100), (20). (C) pabacity . . . : . | 1459°48+4°11 | 1444°32 hiss 1314°5 +6°30 | 1354°5 (L) Lengt. . : . : 187°52+°20 | 184°71 177°97 +°20 177°15 (B) Breadth (maximum) . . | 139°56+°16 139°46 135°16+ 29 136°45 | (B’) Breadth (minimum frontal) . 96°42+°15 99°82 92°66 + '25 96:8 | (H) Height . : . : 132°724°17 129°75 125°01+°31 126°75 (LB) Basi-nasal length . 100°37+°13 98°2 | 93°82+ °20 93°90 | (U,) Horizontal circumference (Turner) 526°60 + °47 523°84 503-61+°71 5059 (S)Sagittalare . . . .| 37860443 | 37202 | 363°15+-68 | 364-9 | (Q) Transverse arc. . . . | 811°10+°36 309°8 | 299'21+°60 302°35 (J) Aygomatic b breadth. . . | 127°16+°18 125°5 118°16+°26 1192 100 B/L : . . 74°36+ 08 75°53 76°03+°19 77:06 100 H/L_. . . . . : 70°81+°09 70°28 ; 70°31+°20 71°79 re H/B . : . : . . 95°144°14 93°04 92°53+°29 92°88 rontal arc . . : : : . | 181°73 128°26 126°96 126°5 Parietal arc . . : . . | 127°00 124°68 | 121°4 121°05 Occipital arc : . . . | 119°88 119°06 | 114°76 117°35 Interstephanic diameter . . | 117-793 120°42 | 114°91 119°85 Asterionic diameter. : . . | 109°68 10857 | 105°44 106°3 Transverse base . . . . . | 11518 114°02 | 108°89 109°4

A glance at the table will show that the mean value of the other measurements is slightly greater in the male non-metopic group than in the metopic series A, while the reverse holds for the B series as compared with the female non-metopic group.

Two exceptions to the general rule exist in the greater frontal breadth in both series. This holds for both the frontal and interstephanic diameters.

It has long been known that the minimum frontal breadth is greater in metopic skulls. Cleland refers to the point in his memoir! on the skull. The late closure of the suture apparently permits the forehead to broaden. Parsons states the increase to be 6 mm. over the normal in the Hythe series, while in Macdonnell’s series the excess was 2°3 mm. in value.

In the present series the mean increase, over the non-metopic groups, in minimum frontal breadth is 3°5 mm. in series A and 4 mm. in series B; the mean increase of the interstephanic diameter is 25 mm. for series A, 5 mm. for series B.

1 Phil, Trans. Roy. Soc. London, vol. clx., 1870,

The cephalic index is higher by one point in the metopic group than in the normal skull, the difference being due, as the mean breadths are practically equal, to the diminution in mean glabello-occipital length.

This greater metopic cephalic index is also shown by the Whitechapel English series, the Moorfields English series, and the Hythe English series of crania, and is evidence of the fact that within the same series the metopic representatives are on the average more brachycephalic than the normal skulls.

The vertical index is little altered, as height and length are apparently proportionately diminished, while the height- -breadth index is slightly reduced owing to the fact that the height is diminished while the breadth remains the same. A reference to the absolute measurements will in the same way explain the differences in the indices in the B series as compared with the non-metopic female group.

While there are notable differences in the relations of the values in the two types of skull to which reference will be made presently, the measurements for minimum frontal breadth and interstephanic breadth stand out from the others as showing a very appreciable change in value in the same direction in passing from the metopic to the non-metopic skull.

An analysis of the values in the A series might incline one at first sight to suggest that, as length and height are reduced in the metopic form while the capacity is not correspondingly diminished, the greater frontal breadth, and consequently the persistence of the suture, might have been necessitated by what may be termed a “compensatory increase” in the frontal region. This has been suggested by various writers. The explanation is rejected by Le Double, and the B series does not tend to support it. The frontal breadth shows a greater divarication than in the A series in favour of the metopic form, while the other measurements remain very slightly in excess of those of the normal group of female skulls.

Here we have an increase in cranial capacity associated with an absolute not a compensatory expansion of the frontal region of the skull. Had the mean capacity in series B fallen, as in series A, below that of the group compared, there would have been the same diminution in length and height and related dimensions as in series A. The two series taken together rather point to metopism, when not due to pathological conditions, being a progressive manifestation. The fact that metopism is rare in the lower races of mankind lends support to this conclusion.


As the frontal breadth is the character found to exhibit a distinct difference in magnitude in the metopic and normal groups, with the excess in favour of the metopic form, we have made the necessary calculations to determine the correlation existing between this and other measurements of the skulls in the series in order to compare the values found with those for the normal group, hoping that by this means some causal factor for the persistence of the suture would be revealed. The great uniformity of the West Scottish series favours such an inquiry. The coefficients calculated are shown in Table II.


. Non-metopic Pair of characters. Metopic group. group.

B’andL . . : . . . “45 + 080 *387 +029 B’andB . . . . woe 59+ °065 389 + °029 B’andH . . : : : : *47+ 080 °28 +:031 BiandC . . : : . . 52+ 073 "42 +:°027 BandL . : ‘ . . : “55 454+ °026 LandH . . . . . . “45 “356 + °029 BandH . : . . : . “45 264+ 031 BandC . . . . : . 72 ‘73 +:017 LandC. . : ; . . “74 69 +°017 HandC . . . . : : “66 56 +°024 CandU.. : : : . : 83 78 +£:°013 CandQ. . . . . . “76 ‘76 +°014 Frontal segment and total sagittal arc . 665 73 +017 Parietal segment and total arc. . 58 538 +025 Occipital segment and total are . . "54 77: £:018

B= Maximum breadth. C=Capacity.

B’= Minimum frontal breadth. U=Horizontal circumference.

L= Maximum length. Q=Transverse arc.

H=Basibregmatic height.

The coefficient of correlation between the minimum frontal breadth and the absolute measurements for length, breadth, and height respectively, is in both series—metopic and non-metopic—greater for breadth than for the other two, so that the minimum frontal breadth shows a greater tendency to increase where the maximum breadth increases than when length and height increase, although it also shows a well-marked and almost similar tendency to do so in the last two cases in the metopic group. .

While the correlation between maximum breadth and capacity shows practically identical values in the two series, indicating that these characters have similar tendencies to vary in metopic and non-metopic forms, the correlation between minimum frontal breadth and capacity is definitely greater in the metopic than in the normal series, a fact which points to a closer relationship between these dimensions in the former than in the latter group. 158 Professor Thomas H. Bryce and Dr Matthew Young

An increase in capacity may be obtained by one or more of the dimensions becoming greater in value. In the normal series it was proved that all three chief diameters tend to increase proportionately as the braincase expands. It would appear that in the metopic series increase in capacity is obtained more frequently, and to a greater extent, by increase _ of the minimum frontal diameter than in the normal series.

From the evidence here supplied it appears that within a uniform series an approximation to a certain capacity is attained by at least two methods— one in which development goes on in what we regard as the normal way with the closure of the metopic suture at an early stage and expansion more particularly in the hinder part of the vault; another in which there is greater growth in the frontal region, associated with the persistence of the suture for a longer period, or till a later age, than normally to permit of such an increase.

The Closure of the Sutures

It is frequently stated that the metopic suture, having persisted till adult life, shows less tendency to fuse than the other sutures, and that it is the last to undergo synostosis. Parsons and Box found no evidence in favour of such a view in the skulls examined by them.

In the present series of 70 skulls three groups may be taken as follows :—

A group A of 29 skulls in which the basal suture has completely fused, and the 3rd molars have either erupted or appear in the cavities of their alveoli, or have failed to erupt. In these 29 skulls all the sutures are open.

Group B of 10 skulls, many edentulous, showing very advanced stages of suture obliteration.

Group C, a middle group of 39 skulls showing various degrees of synostosis, from the very commencement of the process to a fairly advanced stage in some cases.

Groups A and B cannot, obviously, throw any light on the condition of metopism, but it seemed possible that the details in the middle group might provide some further information. The results are shown in Table III.

A consideration of the table brings out the fact, already well known, that synostosis, so far as the outer aspect of the sutures is concerned, begins either in the inferior part of the coronal suture or in the sagittal suture in the region of the obelion.

In this series it is obvious that the closure of the sagittal suture precedes that of the coronal suture, and, what is more interesting, that in Series No.

Observations on Metopism

Table III.

B=bregmatic part. B=bregmaticpart. L=lambdoid part. S=superior par V=vertex. C=complex part. , M=middle part. M=middle part.


O=obelion. T=temporal part. A=asterionic part. I=inferior part.



S=superior part.



needs . Ss 8 S. sagittalis. | S. coronalis, | s. lambdoidea. ‘| s

spheno- spheno


| frontalis, parietal. |

ow x ° a & fo) 4

p+ttr ti | b++t1 +i '++xti | | ! | |




| (+1



\ btl+titi

It (++ 1 1+x 1





1 i ' |

x I I ' I

I x tl l++4+il |


| (+4+xt+! 1+

I i !

i (+xi+xisrti | | ! I |

I [xl

| t+ 1x x) I |

| I ! I 1 | x | | ! ! |

1++1xtix+texeiti + 1

1xxlxwxty 1 |

{ |

i= = > mR = Peal

Edentulous. Edentulous.

8rd molars in alveoli. ‘*crane en toit.”


3rd molars failed. Edentulous.

8rd molars in alveoli. Edentulous.

Edentulous. 3rd molars unerupted.



- =open; +=closed ; x =closing.

In case of difference on two sides, facts represented thus,

Cite this page: Hill, M.A. (2021, March 8) Embryology Paper - Observations on metopism (1917). Retrieved from

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