An Atypical Bronze Age Mandible from Zerniki Gorne, Poland ROBERT H. BIGGERSTAFF University of Kentucky, Albert B. Chandler Medical Center, Department of Orthodontics, Lexington, Kentucky 40506 ABSTRACT The unusual anatomical features of a Bronze Age mandible are described. Of particular interest were the shelf-like ridges which were located approximately midway along the rami. These ridges probably formed the insertion areas for the masseter muscles. Of two possible explanations presented to account for the unusual morphological variations, the more likely is the congenital absence of the superficial portions of the masseter muscles. However, a n alternative explanation is presented suggesting the presence of shortened superficial portions of the masseter muscle which could explain the contour of the shelf. During the summer of 1970, while examining a series of Bronze Age skulls a t Warsaw University, Warsaw, Poland, 1 observed a human mandible with many atypical anatomical features. The skull belonged to a population of 150 skeletons excavated from 95 obvious graves i n a barrow necropolis, located near the village Zerniki Gorne in the Busko district of Kielce county. The site contained three cemeteries with older graves that were disturbed by younger graves. The grave goods facilitated the separation of three distinct cultures on the basis of their cultural affinities: 1. The Corded Ware culture, 2,00&1,900 B.C. (decline of Neolithic). 2. Mierzanowice culture, 1,90&1,600 B.C. (early Bronze Age). 3. Trzciniec culture, 1,600-1,300 B.C. (middle Bronze Age). The above dates are approximations and are based on the similarity of the observed artifacts to other absolutely dated materials. (Unfortunately, I did not record the catalogued description of the culture to which the skull belonged.) The cranium (fig. 1) was poorly preserved and distorted. The maxillae were missing as were portions of the sphenoid and occipital bones. The mandible is shown i n figures 2 through 4. The arrangement of the tooth sockets indicate a “normally” shaped dental arch. The alveoli also suggest that eleven (1 1) teeth were lost post-mortem, three ante-mortem. AM. J. PHYS. ANTHROP..35: 187-192. The posterior molar-containing alveolar processes are situated such that a space results on each side between the molars and ascending ramus (fig. 2) and increases the medial prominence of the mylohyoid line (fig. 4). The areas for the insertion of the masseter muscles are most unusual. The attaching surfaces are located i n the superior and middle thirds of the rami and do not extend inferiorly to the angles and lower borders of the mandible (fig. 2). Instead, wide bony shelves, reminiscent of the eversion often observed a t the angles of Eskimo mandibles, provide the required additional areas of insertion. The lower one-third of the lateral ramal surfaces are smooth and do not appear to be areas of muscle insertion. The mandibular notches are shallow. The condyles are asymmetrical, the right being larger than the left (fig. 3). An exostosis is present at the point of insertion of the left lateral pterygoid muscle on the neck of the condyle. The right condylar neck is regular in appearance. Posterior and slightly inferior to the exostosis on the left condylar neck is a bony spine curving over a groove that passes inferiorly and laterally on the posterior border of the ramus. A similar groove is present on the posterior border of the right ramus; however, this groove terminates in a bony canal on the medial surface of the con1 This research was supported in part by a Research Field Trip Award from the Foreign Currency Exchange Program of the Smithsonian Institute. 187 188 ROBERT H. BIGGERSTAFF Fig. 1 Basal view of the cranium. Fig. 2 Right lateral view of the mandible showing the unusual insertion area of the right masseter muscle. AN ATYPICAL BRONZE AGE POLISH MANDIBLE 189 Fig. 3 Basal view of the mandible. 1. Lower borders of mandible; 2. inferior border of ramal shelves; 3. lingual margins of posterior alveolar bone (note the relationship to the lower borders of the mandible); 4. unusual grooves on the posterior borders of the rami; 5. atypical form for the insertion area of the left lateral pterygoid muscle; 6. the posterior border grooves terminating via bony canals; 7. the semi-canals transmitting the mylohyoid vessels and nerves. dylar neck. A logical or anatomical explanation for these structures is not apparent. Possibly, a n artery and/or vein coursed superiorly deep to the substance of the parotid gland to supply the masseter and lateral pterygoid muscles. (Perhaps there was even a n accessory parotid duct). The shape of each lingula is exaggerated and the mandibular foramina can be observed i n deep fossae (fig. 3 ) distal to the mylohyoid line. The extreme medial placement of the mylohyoid lines and the deep mylohyoid grooves contribute to the depth of the fossae. These mylohyoid lines course anteriorly to terminate in the sublingual foveae (fig. 3). To explain adequately the atypical masseter muscle insertion areas, it is necessary to consider certain biomechanical principles. First, muscle length is not a n important criterion for adequate muscle function. To be sure, the masseter muscles in this individual are approximately two-thirds to three-fourths of their usual length. Yet, the wear pattern observed on the remaining teeth does not indicate abnormal muscle function. Secondly, only the left lateral pterygoid insertion area manifests a n indication of abnormal muscle activity. One might argue that the relatively narrow alveolar processes (as compared to the underlying basal bone) are caused by muscle activity directed laterally, a n observation consistent with the exostosis i n the area of insertion for the left lateral pterygoid. Moreover, the additional buttressing in the areas between the mylohyoid lines and the oblique lines was necessary to compensate for the added stress applied to the superior portions of the rami. Thirdly, the evidence suggests that muscle mass and function were adequate to assure a relatively long survival to the individual, based on the wear of the second and third molars. The adequacy of muscle mass is manifest by the abnormal thickness of the insertion ROBERT H. BIGGERSTAFF 190 Fig. 4 Fronto-cephalic view of the mandible. area on the shelf-like base, a clue that probably provides the solution to the problem. The rnasseter muscle is usually described as a thick, quadrilateral muscle, consisting of two portions. The larger, superficial portion arises by a thick tendon from the zygomatic process of the maxilla and from the anterior two-thirds of the lateral surface of the zygomatic arch (Gray, '66). Its fibers pass obliquely downward to insert into the angle and lower one-half of the ramus of the mandible. The smaller deep portion arises from the posterior one-third of the lower border and the whole of the medial surface of the zygomatic arch. Its fibers pass downward and forward to insert into the upper one-half of the ramus and lateral surface of the coronoid process. The morphological features of the mandible from Zerniki Gor,ne suggest that the superficial portions of the masseters were, in all probability, congenitally absent. The remaining deep portions were obliged to compensate, functionally, for the missing muscle mass. If so, this situation probably required the muscles to become hypertrophied and the areas of insertion to be remodeled into the observed contours in order to sustain the magnitude and direction of functional stresses. If the zygoma were abnormally positioned, either anteriorly, superiorly, or both, a similar result might be observed. This is considered unlikely because the zygomae appear to be normally positioned (fig. 1). An alternative explanation for this phenomenon requires the presence of both the superficial and deep portions of the masseter muscles, but the length of the superficial portions to be shortened to approximately the length of the deep portions. Since the direction of function of the superficial portion is usually directed inferiorly and posteriorly, the area of insertion could be directed obliquely upward as shown i n figure 2. One would not expect the area of the deep portion to be clearly defined if these explanations were true. On the other hand, the deep portion may have extended to the level of the shelf, possibly occupying the medial part of the shelf, while the superficial portion inserted into the lateral part. Both explanations are in accordance with Wolff's law which states that the form of the bone being given, the bone AN ATYPICAL BRONZE AGE POLISH MANDIBLE elements place or displace themselves in the direction of functional pressure. A third alternative remains. Could the inferior part of the superficial portion of the masseter be calcified? If so, the calcified portion need not appear as a n exostosis but could grade insensibly into the usual contour of the mandibular angle. The mandible from Zerniki Gorne, then, represents an exceedingly rare biological expression of the influence of muscle function on bone. More importantly, it provides one with the opportunity to reflect on the infinite possibilities for variation in bone morphology since a careful search of the literature did not reveal a published account of observations analogous to those reported. 191 ACKNOWLEDGMENTS The materials used in this study were made available to me by Prof. dr. Andrzej Wiercinski. They are housed i n the Department of Anthropology, Warsaw University, Warsaw, Poland. I thank Prof. dr. Zdzislaw Rajewski for placing all of the facilities of the Archeological Museum (Warsaw, Poland) at my disposal. Lastly, I thank dr. Krystyna Szlachetko and dr. Alina Wiercinska for invaluable discussions. LITERATURE CITED Gray, H. F. 1966 T h e Anatomy of t h e Human Body. G. M. Goss, e d . Lea a n d Febiger, P h i l a delphia.