K. Miller - Forensic Science Communications - January 2004
January 2004 - Volume 6 - Number 1 |
Research and Technology
A Survey of Tissue-Depth Landmarks for Facial Approximation
Rebecca E. Brown
Computer Scientist
Timothy P. Kelliher
Computer Scientist
Peter H. Tu
Computer Scientist
Wesley D. Turner
Computer Scientist
General Electric Global Research
Imaging Technologies
Niskayuna, New York
Michael A. Taister
Visual Information Specialist
Investigative and Prosecutive Graphics Unit
Kevin W. P. Miller
Research Biologist
Counterterrorism and Forensic Science Research Unit
Federal Bureau of Investigation
Quantico, Virginia
Abstract | Introduction | Tissue-Depth Landmarks
Frontal Bone | Temporal Bone | Zygomatic Bone | Nasal Bone | Maxilla | Mandible
Occipital and Parietal Bones | Discussion | References
Abstract
A common method of three-dimensional forensic facial reconstruction from human remains involves building an approximation of a face directly on the questioned skull using clay. In this method forensic artists place tissue-depth markers at predetermined landmarks distributed around the skull. These markers guide the application of clay to the skull in order to form the final approximation of soft tissue-depth. Although locations and tissue-depth data for many landmarks are published in tissue-depth tables, a standard set of tissue-depth landmarks does not exist. Furthermore, even where different tables refer to the same landmark, there often is no agreed upon definition of the individual landmarks. This leaves the choice of tissue-depth table and the interpretation of the landmarks in the table to the subjective application of the forensic artist. The purpose of this paper is to present the tissue-depth landmarks currently available to forensic artists in order to highlight the need for standardizing the set of landmarks and the landmark definitions used in three-dimensional forensic facial reconstruction.
Introduction
Forensic three-dimensional facial approximation is the process of recreating the countenance of a person based on an unknown or questioned skull. Whereas a number of techniques exist, those in widest use by the forensic community in the United States begin by applying a sparse set of tissue-depth markers at defined landmarks on the skull (Taylor 2001). These markers are then used to guide the application of the clay used to approximate the face. Although forensic anthropologists have collected soft tissue measurements since the late 19th century, consensus on a set of standard landmarks that are used to guide an accurate forensic facial approximation has yet to emerge. Rather, it is largely up to the individual forensic artist to choose tissue depths from any one of a number of tables based on the attributes of a particular questioned skull. The forensic artist then must place the tissue-depth markers on the skull in a manner that approximates the landmark as originally described. Leaving the choice of landmarks and the interpretation of landmark placement up to the forensic artist introduces subjectivity into an approximation. Collecting and categorizing the landmarks included in tissue-depth tables highlight the inconsistencies in current forensic practice that contribute to this subjectivity, and the need for standardizing tissue-depth tables used in forensic facial approximation.
Tissue-Depth Landmarks
The following sections catalog the landmarks defined in the surveyed tissue-depth tables used in forensic facial approximation (Table 1) by the bone in which they are most often located. Each section consists of a table grouping the landmarks by approximate location (Tables 2-9), an image highlighting the approximate locations of the landmarks on the bone (Figures 1-7), and text describing some of the apparent similarities and discontinuities between the tissue-depth landmarks and the methods of measuring the soft tissue depths. In the cases when no description or reference has been given in the text accompanying a tissue-depth table, the description in the table is cross-referenced to a common definition of the landmark (Table 10) given by Bass (1995), Stedman (2000), White (2000), or Taylor (2001). The lack of standards becomes evident from observing the number of landmarks in the tables with multiple, and often conflicting, definitions.
Landmarks on the Frontal Bone
The landmarks on the frontal bone (Table 2, Figure 1) describe the soft tissue depths of the forehead and the upper border of the eye, or orbit. All of the surveyed researchers defined landmarks at the glabella (Landmark 2.6). As shown in Table 2, the exact definition of this point varies from author to author. The tissue-depth tables also each contain a point above the orbit (Landmark 2.8). Sometimes this landmark is defined with respect to the superciliary arch or to the supraorbital ridge. Other times this point is defined with reference to the eyebrow, a soft tissue feature itself, which is not present during a forensic facial approximation. Lebedinskaya et al. (1993) portrayed this landmark as being closer to the midline of the face than the rest of the authors.
The other landmarks on the frontal bone add definition to the forehead. Helmer (1984) added six additional points around the forehead, whereas Manhein et al. (2000) did not add any. Rhine and Campbell (1980) measured separate tissue depths at the supraglabella and the frontal eminence, although, according to Taylor (2001), the current standard practice among forensic artists is to use only the tissue depth at the supraglabella to develop the forehead.
Forensic artists rarely place landmarks above the hairline, because they are covered with a wig or clay representing hair. For this reason, common anthropological landmarks such as vertex and bregma, although included in this discussion for completeness, are not used. Defining landmarks in terms of the soft tissues of the face, which are not available to the forensic artist during the forensic facial approximation, is a recurring issue throughout the tables. In the case of the trichion, a cephalometric point dependent on the hairline, later tissue-depth tables have replaced it with the craniometric landmark metopion or supraglabella. The definitions by Aulsebrook et al. (1996) of supraorbital (US3) and frontal (US1) landmarks, however, depend upon the location of the pupil of the eye. As with the eyebrow, this is not available to a forensic artist when completing a forensic facial approximation. It can be assumed that the numerous references to the eyebrow throughout the table can be directly substituted with the superciliary arch when building a forensic facial approximation.
Landmarks on the Temporal Bone
The temporal bone contains the bony structures around the ear, part of the cheek, and the temple region. Only three landmarks for forensic facial reconstruction, one for each of these regions, are defined on this bone (Table 3, Figure 2). The most commonly defined landmark on the temporal bone is the zygion, also named the lateral or midzygomatic. Since it is defined as the most lateral point, or the highest point, of the zygomatic arch, the location of the zygion in relation to the other bony landmarks is highly variable, dependent on the bone structure of the individual in question. Of the tables surveyed, the majority listed the tissue depth at a single landmark located either on the temporal fossa or near the bony ear, highlighting the existing lack of standardization in the set of landmarks available to the forensic artist.
Landmarks on the Zygomatic Bone
The zygomatic bone, commonly known as the cheekbone, consists of much of the cheek along with the lower and the outer borders of the orbit (Table 4, Figure 3). Two of the landmarks define the borders of the eye orbit, although twice as many researchers defined the landmark on the lower border as on the outside edge. As on the frontal bone, those landmarks around the eye socket are often defined in terms of the soft tissue of the eye. Further research is needed to determine if such references affect the accuracy of a reconstruction in such a way to change the recognition rate. The researchers surveyed do not agree on the name or a consistent definition of the one landmark located in the cheek region. Rhine and Campbell (1980), Lebedinskaya et al. (1993), and Manhein et al. (2000) refer to it as the lateral orbit, the malare, and the zygomatic, respectively.
Landmarks on the Nasal Bone
The nasal bone (Table 5, Figure 4) has the fewest landmarks for forensic facial approximation and perhaps for this reason the researchers for the most part agree on those locations. Of the researchers surveyed, all placed a landmark at the root of the nasal bone (nasion) and all except His (1895) placed another at the tip (rhinion). His instead placed a second landmark along the midline of the nasal bone.
Landmarks on the Maxilla Bone
The maxilla (Table 6, Figure 5) encompasses many areas of the face, including the sides of the nasal opening, the lower cheek, and the upper half of the mouth. The researchers surveyed did not agree on the number or the locations of the landmarks on this bone. While early researchers concentrated on two landmarks between the nose and the mouth (subnasale and philtrum), later researchers added greater definition through landmarks around both the nose and the upper mouth. Aulsebrook et al. (1996) defined 16 landmarks on the maxilla; many of them only slight variations of each other and differing primarily based on the angle the measurement was taken from the skull. One of these sets, at the nose tip (LR6, LR7, LR8), is dependent on the soft tissue of the known face being measured and is impossible to recreate on a questioned skull. Similarly, the nostril measurement of Manhein et al. (2000) depends on the existence of a complete nose to place accurately.
Overall, the landmarks located on the nasal bone and around the nasal opening on the maxilla give little information to the forensic artist on the structure of the soft tissues of the nose. There is insufficient research to conclude that the shape and the size of the nose can be determined solely based on the bone structure of the skull. Forensic artists typically use their artistic skill and rough heuristics to guide forensic facial approximations in this area. In addition, forensic artists feel that the tissue-depth measurements at the inferior malar (Landmark 6.5) and the supra-M2 (Landmark 6.6), along with the sub-M2 (Landmark 7.2), are too shallow to provide accurate guidance in a forensic facial approximation. Instead, they build the soft tissues of the cheek and the jaw directly based on the skull of the individual in question, taking into account the musculature and facial expression (Taylor 2001).
Landmarks on the Mandible Bone
The mandible (Table 7, Figure 6), covering the lower mouth, the chin, and the lower jaw, not only contains the greatest number of defined landmarks, but it is also the region with the most landmarks common among the researchers. Although they disagree on its name, each placed a landmark at the deepest point along the midline between the lower lip and the chin. They also located landmarks at the pogonion, or mental eminence, and under the chin. George (1987, 1993) defined two points under the chin, the gnathion and the menton. The other researchers surveyed measured at only one landmark, and it is often unclear which landmark they are referring to based on the definitions in the text, or lack thereof. Most of the researchers placed a landmark along the edge of the jaw, although they defined different locations for this landmark. Over half were defined in relation to the masseter muscle or its insertion point on the lower jaw, making it difficult to accurately locate without sufficient training in anatomy.
Landmarks on the Occipital and Parietal Bones
The soft tissue covering the occipital (Table 8, Figure 7) and parietal bones (Table 9, Figure 7) do not directly affect a facial approximation. Suzuki (1948), Helmer (1984), and George (1993), however, have included landmarks from these bones in their respective tables, and the landmarks are included here to provide a complete list of the landmarks on the skull at which soft tissue depths have been measured.
Discussion
A key element of using the tissue-depth tables to guide a facial approximation is the dependence on a particular published set of average tissue depths. Whereas the errors in obtaining such measurements have decreased through the use of newer and more rigorous methods, the issues inherent in the use of the tissue-depth tables have instead increased in complexity with each new table published.
The primary issue concerns the need for standardizing the landmarks of the tissue-depth table used in the forensic reconstruction of facial features from human remains. As shown above, the researchers surveyed choose their own set of landmarks at which to measure the tissue depths. As such, few of the tissue-depth tables surveyed list a standard set of landmarks that would provide an accurate guide for the forensic artist. The five landmarks common to all of the tables, the glabella, the nasion, the chin-lip groove, the pogonion, and the gnathion, are all located along the midline of the face. One possible cause of the lack of common landmarks is the difficulty of accurately locating well-defined craniometric landmarks through the soft tissues of a cadaver or, conversely, the difficulty of locating landmarks on the questioned skull that have been defined in terms of the soft tissue. Other causes could include the selective choosing of landmarks used in previously published tissue-depth tables and the selection of landmarks based on the personal preference of the researcher. Whatever the reason, the lack of a standardized set of landmarks to guide the forensic artist makes the objective evaluation of a forensic facial approximation difficult.
A second issue highlighted by the need for standardization and by the above list of landmarks is the lack of a concrete set of definitions. Half of the tissue-depth tables surveyed neither include nor reference definitions for all of the landmarks listed. The lack of a definition is most apparent when the landmark is not a craniometric landmark but describes a region of the face, such as fossa canina (Lebedinskaya et al. 1993) or is a general term that cannot be completely defined by a dictionary or textbook, such as end of nasal (Rhine and Campbell 1980). Other nonconformities occur when two tissue-depth tables claim to measure at the same location on the skull but have definitions different from each other and/or a so-called common knowledge definition, such as the root of the zygoma (Aulsebrook et al. 1996; Manhein et al. 2000) and the gnathion and the menton (all). The forensic artist is left to assume that an undefined landmark is defined by the common-knowledge definition, which induces subjectivity into the use of the tissue-depth tables and, therefore, the facial approximation. Even when the definition of a landmark is given or is common knowledge, the definition may not give all the necessary information for the forensic artist to place the landmark correctly during a forensic facial approximation. With the exception of George (1993) and Aulsebrook et al. (1996), the definitions do not include information regarding the angle of measurement of the landmarks in relation to the skull. Without this, the forensic artist cannot reliably reproduce the placement of the landmarks as intended by the forensic anthropologist.
Due to the lack of standardization in the landmarks and their definitions used in the tissue-depth tables, the forensic artist is given the leeway to not only choose the table of preference but also the leeway to interpret the location of the landmarks. For example, Taylor (2001) suggests that five of the landmarks defined by Rhine et al. (Rhine and Campbell 1980; Rhine and Moore 1982) are not useful to a forensic artist and should, therefore, be ignored during a three-dimensional forensic facial approximation. This induces a level of subjectivity into the use of the landmarks and the facial approximation itself. Given a questioned skull and a set of anthropological data about the individual in question (sex, race, age, height, weight, stature), it is not possible for a forensic artist to develop an objective and repeatable forensic facial approximation. The first solution to correct this issue is to develop a standard set of landmarks and definitions that could guide a forensic artist to repeatedly and reliably create a recognizable facial approximation. Further solutions could include developing an automatic method for placing the landmarks on the skull to rely less on the interpretation of the accurate location by the forensic artist and perhaps introducing a new objective method of facial approximation that does not depend on the subjective choices of the forensic artists.
References
Aulsebrook, W. A., Becker, P. J., and Iscan, M. Y. Facial soft tissue thickness in the adult male Zulu, Forensic Science International (1996) 79:83-102.
Bass, W. M. Human Osteology: A Laboratory and Field Manual. Missouri Archaeological Society, 1995.
Campbell, C. E. A problem in human variation: The facial tissue thicknesses of Caucasoids, Negroids, and Mongoloids. Doctoral thesis, University of New Mexico, Albuquerque, New Mexico, 1981.
George, R. M. Anatomical and artistic guidelines for forensic facial reconstruction. In: Forensic Analysis of the Skull. M. Y. Iscan and R. P. Helmer, eds. Wiley-Liss, New York, 1993, pp. 215-227.
George, R. M. The lateral craniographic method of facial reconstruction, Journal of Forensic Sciences (1987) 32:1305-1330.
Helmer, R. Schädelidentifizierung durch Elektronische Bildmischung. Kriminalstik-Verlag, Heidelberg, 1984.
His, W. Anatomische Forschungen über Johann Sebastian Bach’s Gebeine und Antlitz nebst Bemerkungen über Dessen Bilder. In: Abhandlungen der Mathematisch-Physischen classe Der Königlich Sächsischen Gesellschaft der Wissenschaften. Bei S. Hirzel, Leipzig, 1895, pp. 379-420.
Kollmann, J. and Büchly, W. Die persistenz der rassen und die reconstruction der physiognomie prähistorischer Schädel, Archiv fur Anthropologie (1898) 25:329-359.
Lebedinskaya, G. V., Balueva, T. S., and Veselovskaya, E. V. Principles of facial reconstruction. In: Forensic Analysis of the Skull. M. Y. Iscan and R. P. Helmer, eds. Wiley-Liss, New York, 1993, pp. 183-98.
Manhein, M. H., Listi, G. A., Barsley, R. E., Musselman, R., Barrow, N. E., and Ubelaker, D. In vivo facial tissue-depth measurements for children and adults, Journal of Forensic Sciences (2000) 45:48-60.
Phillips, V. M. and Smuts, N. A. Facial reconstruction: Utilization of computerized tomography to measure facial tissue thickness in a mixed racial population, Forensic Science International (1996) 83:51-59.
Rhine, J. S. and Campbell, H. R. Thickness of facial tissues in American Blacks, Journal of Forensic Sciences (1980) 25:847-858.
Rhine, J. S. and Moore, C. E. Facial reproduction tables for facial tissue thickness of American Caucasoids in forensic anthropology. Maxwell Museum Technical Series No 1, 1982.
Stedman, T. L. Stedman’s Medical Dictionary. Lippincott Williams and Wilkins, New York, 2000.
Suzuki, K. On the thickness of the soft parts of the Japanese face, Journal of the Anthropological Society of Nippon (1948) 60:7-11.
Taylor, K. T. Forensic Art and Illustration. CRC, New York, 2001.
White, T. D. Human Osteology. Academic, New York, 2000.
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* Rhine and Campbell (1980) and Rhine and Moore (1982) measured tissue depths at the same landmarks.
† George (1993) did not include tissue-depth measurements.
‡ Phillips and Smuts (1996) measured tissue depths at the same landmarks as Rhine and Campbell (1980), but they measured the lateral landmarks on only one side of the face.
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* See Table 10
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* See Table 10
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* See Table 10
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* See Table 10
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* See Table 10
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* See Table 10
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* See Table 10
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* See Table 10
Landmark | Definition | Reference | Table |
alare | the instrumentally determined most lateral point on the nasal aperture taken perpendicular to the nasal height | Bass (1995) | 6 |
beneath chin | the lowest point on the mandible | Taylor (2001) | 7 |
chin | the anterior projection of the inferior border of the body of the mandible | Bass (1995) | 7 |
chin fissure | a deep furrow, cleft, or slit in the chin | Stedman (2000) | 7 |
chin-lip fold | a ridge or margin apparently formed by the doubling back of a lamina between the chin and lip | Stedman (2000) | 7 |
ectoconchion | the point where the orbital length line, parallel to the upper border, meets the outer rim. The point of maximum breadth on the lateral wall of the eye orbit | Bass (1995) | 4 |
end of nasal | the anterior tip or the farthest point {it out} on the nasal bones | Taylor (2001) | 5 |
euryon | the two points on the opposite sides of the skull that form the termini of the lines of greatest breadth | Bass (1995) | 9 |
fossa canina | hollow of variable extent located on the facial surface just below the infraorbital formamen, where the zygomatic, frontal, and alveolar processes of the maxilla come together | White (2000) | 6 |
frontal eminence | bony projection of the ectocranial surface of the frontal bone | White (2000) | 2 |
frontotemporale | the most medial point on the incurve of the temporal ridge, the points lie on the frontal bones just above the zygomaticofrontal suture. | Bass (1995) | 2 |
glabella | the most forward projecting point in the midline of the forehead at the level of the supraorbital ridges and above the nasofrontal suture | Bass (1995) | 2 |
gnathion | the lowest median point on the lower border of the mandible | Bass (1995) | 7 |
gonion | the midpoint of the angle of the mandible between body and ramus | Bass (1995) | 7 |
inferior labial sulcus | a furrow between the developing lower lip and gum | Stedman (2000) | 7 |
inferior malar | the lowest part of the cheek, or cheek bone | Stedman (2000) | 6 |
labrale inferius | a point where the boundary of the vermilion border of the lower lip and the skin is intersected by the median plane | Stedman (2000) | 7 |
labrale superius | the point on the upper lip lying in the median sagittal plane on a line drawn across the boundary of the vermilion border and skin | Stedman (2000) | 6 |
lateral orbit | drop a line from the outer margin of the orbit and place the marker about 10mm below the orbit | Taylor (2001) | 4 |
lower lip margin | centered between the mandibular (lower) central incisors at the level of the cementum enamel junction | Taylor (2001) | 7 |
m1 | the first upper molar | Bass (1995) | 6 |
m1 | the first lower molar | Bass (1995) | 7 |
mandibular body | the thick bony part of the mandible that anchors the teeth | White (2000) | 7 |
mandibular branch | the mandibular ramus; the upturned perpendicular extremity of the mandible on either side | Stedman (2000) | 7 |
maxillary | relating to the maxilla, or upper jaw | Stedman (2000) | 6 |
mental eminence | the triangular eminence, or bony chin, at the base of the corpus in the anterior symphyseal region (mental protuberance) | White (2000) | 7 |
menton | in cephalometrics, the lowermost point in the symphyseal shadow as seen on a lateral jaw projection | Stedman (2000) | 7 |
metopion | an instrumentally determined, ectocranial midline point on the frontal where the frontal’s elevation above the chord from the nasion to the bregma is the greatest | White (2000) | 2 |
nasion | intersection of the nasofrontal suture with the midsagittal plane | Bass (1995) | 5 |
occlusal line | line pertaining to the contacting surfaces of the posterior teeth | Stedman (2000) | 7 |
ohryon | the point on the midline of the forehead just above the glabella (supranasal point, supraorbital point) | Stedman (2000) | 2 |
opisthocranion | the most posterior point on the skull not on the external occipital protuberance; the posterior end point of maximum cranial length measured from glabella | Bass (1995) | 8 |
orbitale | the lowest point in the margin of the orbit | Bass (1995) | 4 |
piltrum | the infranasal depression; the groove in the midline of the upper lip | Stedman (2000) | 6 |
pogonion | the most anterior point in the midline of the chin | Bass (1995) | 7 |
rhinion | the midline point at the inferior free end of the internal suture | White (2000) | 5 |
stomiom | the median point of the oral slit when the lips are closed | Stedman (2000) | 6 |
sub-m2 | below the second lower molar | Bass (1995) | 7 |
subnasale | under the nose | Stedman (2000) | 6 |
suborbital | infraorbital, below or beneath the orbit | Stedman (2000) | 4 |
sulcus-labio-mentalis | the indistinct line separating the lower lip from the chin | Stedman (2000) | 7 |
superciliary arches | curved projections above orbits (brow ridges) | Bass (1995) | 2 |
superior labial sulcus | a furrow between the developing upper lip and gum | Stedman (2000) | 6 |
supracanine | above the canine tooth | Bass (1995) | 6 |
supraglabella | a position above the glabella | Stedman (2000) | 2 |
supraglenoid | above the glenoid cavity or fossa | Stedman (2000) | 3 |
supra-m2 | above the second upper molar | Bass (1995) | 6 |
supraorbital border | upper edge of the eye orbit | Bass (1995) | 2 |
suprapogonion | a position above the pogonion | Stedman (2000) | 7 |
trichion | a cephalometric point at the midpoint of the hairline at the top of the forehead | Stedman (2000) | 2 |
upper lip margin | centered between the maxillary (upper) central incisors at the level of the cementum enamel junction | Taylor (2001) | 6 |
vertex | the highest point in the midsagittal contour, as seen from norma lateralis, when the cranium is in the frankfort horizontal | Bass (1995) | 2 |
zygion | the most lateral point of the zygomatic arch; a point determined instrumentally | Bass (1995) | 3,7 |
zygomatic arch | the arch formed by the temporal process of the zygomatic bone that joins the zygomatic process of the temporal bone | Stedman (2000) | 3 |
zygomaxillare | the most inferior point on the zygomaticomaxillary suture | White (2000) | 4,6 |
Figures
Figure 1: Representation of landmarks on the frontal bone: 2.1, vertex; 2.2, bregma; 2.3, trichion; 2.4, metopion; 2.5, ophryon; 2.6, glabella; 2.7, lateral glabella; 2.8, supraorbital; 2.9, frontal eminence; 2.10, lateral frontal; 2.11, frontotemporale.
Figure 2: Representation of landmarks on the temporal bone: 3.1, temporal fossa; 3.2, root of zygoma; 3.3, zygion.
Figure 3: Representation of landmarks on the zygomatic bone: 4.1, zygomatic; 4.2, ectoconchion; 4.3, orbitale.
Figure 4: Representation of landmarks on the nasal bone: 5.1, nasion; 5.2, midnasal; 5.3, rhinion.
Figure 5: Representation of landmarks on the maxilla: 6.1, dacryon; 6.2, lateral nasal; 6.3, alare; 6.4, fossa canina; 6.5, zygomaxillare; 6.6, supra-M2; 6.7, supracommissural; 6.8, subnasale; 6.9, midphiltrum; 6.10, prosthion; 6.11, stomion.
Figure 6: Representation of landmarks on the mandible: 7.1, infradentale; 7.2, sub-M2; 7.3, occlusal line; 7.4, subcommissural; 7.5, chin-lip fold; 7.6, suprapogonion; 7.7, pogonion; 7.8, gnathion; 7.9, mental tubercle, anterior; 7.10, border of the mandible; 7.11, middle of the mandibular body; 7.12, insertion of masseter, anterior; 7.13, insertion of masseter, posterior; 7.14, gonion; 7.15, mandibular branch.
Figure 7: Representation of landmarks on the occipital and parietal bones: 8.1, opisthocranion; 8.2, inion; 9.1, lambda; 9.2, euryon.