AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 82:179-181(1990)

Mylohyoid and Jugular Foramen Bridging in Pre-Columbian Chileans DANNY R. SAWYER, VINCENT GIANFORTUNE, MICHAEL L. KIELY, AND MARVIN J. ALLISON Departments of Oral and General Pathology (D.R.S., V.G.) and Anatomy arzd Oral Biology (M.L.K.), Loyola University of Chicago School of Dentistry, Muywood, Illinois 60153; Department of Anthropology, Institute of Anthropology and Archaeology, University of Tarapaca, Arica, Chile (M.J.A.)

KEY WORDS

Discrete traits, Human skull, Osteology

ABSTRACT

The occurrence of mylohyoid groove bridging and jugular foramen bridging was determined in a population of adult Pre-Columbian Chileans. Two hundred forty-one crania (110 males, 131 females) were examined for jugular foramen bridging and 464 mandibles (252 males and 212 females) were observed for mylohyoid groove bridging. The overall incidence of jugular foramen bridging was 14.94%, with females showing a higher occurrence (18.32%)than males (10.91%);however, no statistical significance was found between the sexes. The right side showed a greater incidence than the left, but again no statistical difference was noted and the occurrence of this trait was found to be associated between the sides. This frequency of jugular foramen bridging is higher than that found in other studies and approaches that reported in North American Eskimo populations. In the case of mylohyoid groove bridging, the incidence was 4.09%with no difference found between the sexes. This frequency of occurrence is less than the values reported previously for the other American populations of Mongoloid ancestry including the Pre-Columbian Peruvian population. The importance of nonmetric skeletal traits for defining population groups and their usefulness as anthropological tools is discussed. It is concluded that hard tissue variations such as bony bridging may be reliable markers to aid in discretely identifying population groups, but their importance can be significantly enhanced by coupling as many traits as possible in future studies. During the past decade, there has been a marked increase in interest in discrete cranial traits. The mylohyoid bridge has received considerable attention over this period (Corruccini, 1972, 1974; Dodo, 1974; Ossenberg, 1974; Sawyer et al., 1978;Lundy, 1980; Kaul and Pathak, 1984; Sawyer and Kiely, 1987). This bridge is formed when the mylohyoid groove on the medial surface of the mandible is converted into a canal by an anomalous bone formation. The mylohyoid bridge is a discrete trait whose suitability as a genetic marker has been questioned (Lundy, 1980). However, other authors still favor studying this trait for it may yet prove useful in population studies if coupled with many other such markers (Sawyer et al., 1978).

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Quite recently there has been renewed interest in the jugular foramen bridge (Dodo, 1986a,b; Sawyer and Kiely, 1987). This interest was generated in part by the report (Dodo, 1986a) that genetic factors in the expression of the jugular foramen bridge may be operating, since this bridge is observed with almost equal frequency in both adult and fetal crania. Thus postnatal environmental factors would seem to have little, if any, influence on the development of this bridge. The bridging of the jugular foramen is accomplished by bony contact of the intrajugular process ofthe temporal bone with the bony process of the occipital bone projecting Received September 27,1988; accepted July 12, 1989.

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D.R. SAWYER ET AL.

either from above or posterior to the hypoglossal canal. Occasionally, two bridges are present and thus a tripartite com artment is formed when both processes o f t e occipital bone contact the intrajugular process of the temporal bone. The purpose of this article is to provide additional data on the occurrence of the mylohyoid and the jugular foramen bridges in another population group, the Pre-Columbian Chilean population.

K

MATERIALS AND METHODS

Two hundred forty-one adult crania, 110 males and 131 females, were examined by direct visualization for the presence of the jugular foramen bridge. Four hundred sixtyfour adult mandibles, 252 males and 212 females, were likewise examined for the presence of mylohyoid bridges. For a complete anatomical description of these bridges and their variations, see Sawyer et al. (1978), Kaul and Pathak (1984), and Dodo (1986a,b). The crania examined were part of mummified and skeletal material found in the northern part of present day Chile. The material is presently housed in the Instituto de Antropologia y Arquelogia of the Universidad de Tarapaca, Arica, Chile. Crania from mummies representing 10 cultures and three geographical areas-coastal, valley, and sierra and mountain regions-were included in this study. The cultures and the approximate dates of their existences were Chinchorro, 5860 B.C.-1720 B.C.; Quiani, 1600 B.C.-950 B.C.; Azapa, 1300 B.C.-600 B.C.; Faldas Del Morro, 900 B.C.-200 B.C.; Alto Ramirez, 900 B.C.-1 A.D.; El Laucho, 500 B.C.-1 A.D.; Cabuza, 300A.D.-700A.D.; Maitas-Chiribaya, 850 A.D.-1000 A.D.; San Miguel, 1100 A.D.-1200 A.D.; and Gentilar, 1200 A.D.-1400 A.D. Sex identification of the mummies and skeletal material was carried out according to the methods of Allison and Gerszten (1975). For the purpose of maintaining consistency with the results of previous studies, the number of jugular bridges is reported as the number of crania exhibiting the bridge (Dodo, 1986a; Sawyer and Kiely, 1987). Additionally, to maintain comparability the number of mylohyoid bridges as seen bilaterally, rather than the number of crania exhibiting this bridge irrespective of the number of bridges, is reported (Ossenberg, 1974; Sawyer et al., 1978; Kaul and Pathak. 1984: Sawyer and Kiely, 1987).

RESULTS

The frequency of occurrence in jugular foramen bridging was 14.94% (36/241). Differences in the incidence of jugular foramen bridgmg between the sexes and the sides (right and left) are shown in Table 1. The incidence of jugular bridging was 12410 (10.91%) in males and 241131 (18.32%) in females. The incidence of jugular foramen bridging was found to be 25/241 (10.37%)on the right side and 16041 (6.64%)on the left in this Pre-Columbian Chilean population. On statistical analyses neither the difference between the sexes nor the sides was found to be significant. However, it was observed that the right jugular foramina were larger more frequently than the left. A 2 x 2 contingency table was constructed in order to test the independence of occurrence of the jugular foramen bridging trait. As shown in Table 2 a statistically significant association was found between sides (P= 0.0046). Thus, in the Pre-Columbian Chilean population examined] the occurrence of jugular foramen bridging is apparently associated between the sides. The frequency of expression of the mylohyoid bridge, as shown in Table 3, was found to be 4.09% (19/464). No significant difference was found between the sexes.

TABLE 1. Sex and side differences in the incidence of jugular foramen bridging in a population of Pre-Columbian Chileans

Sex' Male Female Total Side2 Right Left

N

+

'W

110 131 24 1

12 24 36

10.91 18.32 14.94

24 1 24 1

25 16

10.37 6.64

x,

1 2 -258fi,df-l,P=0.1079iN.S.). -

2 X L = 2 159, df = 1, P = 0.1417 (N.S.).

T A B L E 2. Association hetween sides in the occurrence o f jugular foramen bridging'

+

Right

-

N

11 205 216

16 225 24 1

Left

+ -

N 1 2 -

x

-

5 20 25

8.034, df = 1, P = 0.0046 (significant difference)

MYLOHYOID AND JUGULAR FORAMEN BRIDGING TABLE 3. Incidence of expression of mylohyoid bridge' 2N

With bridge Unilateral Bilateral number P7i) number PXJ number MI)

Sex

Male Female Total

' x2

252 212 464

= 1.482, df = 3,

44 (17.46) 31 (14.62) 75 (16.16)

22 (8.73) 15 (7.08)

37 (7.97)

11 (4.37) 8 (3.77) 19 (4.09)

P = 0.6864 (N.S.).

DISCUSSION

The incidence of jugular foramen bridging in the present population studied is higher (14.94%)than the other published reports on Asian Mongoloid and other populations and this frequency approaches that reported for the North American Eskimo populations which, of course, are of Mongoloid ancestry (Dodo, 1986a; Sawyer and Kiely, 1987).Also, as reported by the above authors, no statistically significant difference was found in the incidence of jugular foramen bridging between the sexes or the sides in the present study on Chileans. Our observation that the right jugular foramina were frequently larger than the corresponding left was also shown by Oetterking (1930) and by Akabori (1933). Czarnetzki (1971) reported that many bilaterally occurring nonmetric skeletal traits show a tendency to associate between the sides. This association was observed in the present Pre-Columbian Chilean population and it was also shown in the jugular foramen bridge in the North American Eskimo (Dado, 1986a) and in Asian Indians (Sawyer and Kely, 1987). The incidence of mylohyoid bridging was less (4.09%)in the present study than that reported for other New World populations of Mongoloid extraction (Kaul and Pathak, 1984), including the earlier Pre-Columbian Peruvian population (Sawyer et al., 1978). The observations also differ in another way, i.e., the Pre-Columbian Peruvian population showed a significantly higher incidence of mylohyoid bridging in females. No difference was found between the sexes in the PreColumbian Chilean population. The majority of other previous studies have also reported no sexual difference in the frequency of occurrence of mylohyoid bridging. A nonmetric trait in the human cranium by itself appears not to provide enough discretionary information to characterize popu-

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lation groups and, therefore, has limited usefulness as an anthropological tool. Future studies should concentrate on collectingdata from as many skeletal traits as possible within the sample population so that the wide range of values on the frequency of occurrence of single traits, as reported in the literature, can be minimized. Certain discrete cranial variations such as jugular foramen bridging, if studied together with several other reliable traits within single populations, could provide more specific and complete information concerning the ethnohistorical background of these population groups. ACKNOWLEDGMENTS

This investigation was supported by a grant from the Loyola University of Chicago School of Dentistry, Research Committee. LITERATURE CITED Akabori E (1933) Crania Nipponica Recentia I. Jpn. J. Med. Sci. 4531-315. Allison MJ, and Gerszten E (1975) Paleopathology in Peruvian mummies. Application of modern techniques. Richmond: Virginia Commonwealth University Press. Corruccini RS (1972) The biological relationships of some prehistoric and historic Pueblo populations. Am. J. Phys. Anthropol. 37t373-388. Corruccini RS (1974)An examination of the meaning of the cranial discrete traits for human skeletal biological studies. Am. J. Phys. Anthropol. 4Ot425-445. Czarnetzki A (1971) Epigenetische Skelettmerkmale im Populations-Vergleich. I. Rechts-Links-Unterschiede Bilateral Angelegter Merkmale. Z. Morphol. AnthroPOI. 63t238-254. Dodo Y (1974) Non-metrical cranial traits in the Hokkaido Ainu and the northern Japanese of recent times. J. Anthropol. SOC. Nippon 82t31-51. Dodo Y (1986a) A population study of the jugular foramen bridging of the human cranium. Am. J. Phys. Anthropol. 69t15-19. Dodo Y (1986b)Observations on the bony bridging of the jugular foramen in man. J. Anat. 144t153-165. Kaul SS, and Pathak RK (1984)The mylohoid bridge in four population samples from India, with observations on its suitability as a genetic marker. Am. J. Phys. Anthropol .65t213-2 18. Lundy JK (1980)The mylohyoid bridge in the Khoisan of southern Africa and its suitability as a mongoloid genetic marker. Am. J. Phys. Anthropol. 53t43-48. Oetterking B (1930) Craniology of the North Pacific Coast. Mem. American Museum of Natural History. VOl. 11. Ossenberg NS (1974) The mylohyoid bridge: An anomalous derivative of Meckel's cartilage. J. Dent. Res. 53:77-82. Sawyer DR, Allison MJ, Elzay RP, and Pezzia A (1978) The mylohyoid bridge of Pre-Columbian Peruvians. Am. J. Phys. Anthropol. 48:9-16. Sawyer DR, and K d y ML (1987) Jugular foramen and mylohyoid bridging in an Asian Indian population. Am. J. Phys. Anthropol. 72t473-477.

Mylohyoid and jugular foramen bridging in pre-Columbian Chileans.

The occurrence of mylohyoid groove bridging and jugular foramen bridging was determined in a population of adult Pre-Columbian Chileans. Two hundred f...
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