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An atypical Bronze Age mandible from erniki Grne Poland.

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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.
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