Human Facial Skeleton Research Articles

Features and networks of the mandible on computed tomography.

The mandible or lower jaw is the largest and hardest bone in the human facial skeleton. Fractures of the mandible are reported to be a common facial trauma in emergency medicine and gaining insights into mandibular morphology in different facial types can be helpful for trauma treatment. Furthermore, features of the mandible play an important role in forensics and anthropology for identifying gender and individuals. Thus, discovering hidden information of the mandible can benefit interdisciplinary research. Here, for the first time, a method of artificial intelligence-based nonlinear dynamics and network analysis are used for discovering dissimilar and similar radiographic features of mandibles between male and female subjects. Using a public dataset of 10 computed tomography scans of mandibles, the results suggest a difference in the distribution of spatial autocorrelation between genders, uniqueness in network topologies among individuals and shared values in recurrence quantification.

Insight into age-related changes of the human facial skeleton based on medieval European osteological collection

Aging changes in the facial skeleton are concentrated mostly in orbits, maxilla and mandible. The aim of this study was to analyze metric traits of the adult viscerocranium in a medieval sample from Cedynia (Poland, Central Europe) and confront the results with literature data for modern populations. It was assumed that diet-related greater biomechanical forces generated during mastication in medieval versus modern times led to slower rate of bone resorption with age. 3D models of the facial skeleton are created for 230 individuals, categorized into young, middle and old adults, and a subgroup of edentulous middle adults is distinguished. Orbits, piriform aperture, maxilla and mandible are measured using Geomagic Studio 12 and analyzed among age categories as well as dentate and edentulous subgroups. The values of the orbital and piriform aperture measurements tend to increase with age and reached statistical significance in males (right orbit height, left orbit width, piriform aperture surface area). In females, maxillary height significantly decrease at right first premolar and first molar, together with height of the right mandibular ramus. In edentulous individuals of both sexes the orbits are wider, and maxillary and mandibular heights are lower than in dentate individuals. This study reveals similar character and direction of the aging process of the facial skeleton in medieval and modern adults, however slower rate of resorptive changes is found in the former sample, which suggests, that diet-related biomechanical forces can influence intensification of the aging processes in the facial skeleton.

A 10-year retrospective study on mandibular fractures in Northern Taiwan

Background/purposeThe mandible is an independent and protruding bone structure in the lower third portion of the human facial skeleton. Because of its prominent and unprotected position, the mandible is a primary site of facial trauma. Previous studies have not comprehensively discussed the association between the mandibular fractures and concomitant fractures of facial bones, the trunk, or limbs. This study analyzed the epidemiology of mandibular fractures and their correlation with concomitant fractures. Materials and methodsThe present study enrolled 118 patients with a total of 202 mandibular fracture sites during at any time from January 1, 2012, to December 31, 2021, in northern Taiwan. ResultsAccording to the study results, the patients between 21 and 30 years of age had the highest occurrence of trauma, and road traffic accidents (RTAs) constituted the primary cause of mandibular fractures. Fall-related injuries were significant in patients >30 years of age. By the analysis of Pearson's contingency coefficient, the number of mandibular fractures was not significantly associated with concomitant fractures of the extremities or the trunk. However, accompanying maxillary fractures can be regarded as an indication of concomitant extremity or trunk fractures in patients with mandibular fractures. ConclusionThree-site mandibular fractures are not necessarily accompanied by extremity and trunk fractures; however, clinicians should implement multidisciplinary examination and management in patients with mandibular fractures accompanied by maxillary fractures. Maxillary fractures can be regarded as an indication of concomitant fractures of other facial bones, the extremities, or the trunk.

Objective analysis of facial bone fracture CT images using curvature measurement in a surface mesh model

The human facial skeleton consists of multiple segments and causes difficulty during analytic processes. We developed image analysis software to quantify the amount of injury and validate the smooth curvature of the surface after facial bone reduction surgery. Three-dimensional computed tomography images of facial bone were obtained from 40 patients who had undergone open reduction surgery to treat unilateral zygomaticomaxillary fractures. Analytic software was developed based on the discrete curvature of a triangular mesh model. The discrete curvature values were compared before and after surgery using two regions of interest. For the inferior orbital rim, the weighted average of curvature changed from 0.543 ± 0.034 to 0.458 ± 0.042. For the anterior maxilla, the weighted average of curvature changed from 0.596 ± 0.02 to 0.481 ± 0.031, showing a significant decrement (P < 0.05). The curvature was further compared with the unaffected side using the Bray–Curtis similarity index (BCSI). The BCSI of the inferior orbital rim changed from 0.802 ± 0.041 to 0.904 ± 0.015, and that for the anterior maxilla changed from 0.797 ± 0.029 to 0.84 ± 0.025, demonstrating increased similarity (P < 0.05). In computational biology, adequate analytic software is crucial. The newly developed software demonstrated significant differentiation between pre- and postoperative curvature values. Modification of formulas and software will lead to further advancements.

A 3D analysis of growth trajectory and integration during early human prenatal facial growth

Significant shape changes in the human facial skeleton occur in the early prenatal period, and understanding this process is critical for studying a myriad of congenital facial anomalies. However, quantifying and visualizing human fetal facial growth has been challenging. Here, we applied quantitative geometric morphometrics (GM) to high-resolution magnetic resonance images of human embryo and fetuses, to comprehensively analyze facial growth. We utilized non-linear growth estimation and GM methods to assess integrated epigenetic growth between masticatory muscles and associated bones. Our results show that the growth trajectory of the human face in the early prenatal period follows a curved line with three flexion points. Significant antero-posterior development occurs early, resulting in a shift from a mandibular prognathic to relatively orthognathic appearance, followed by expansion in the lateral direction. Furthermore, during this time, the development of the zygoma and the mandibular ramus is closely integrated with the masseter muscle.

The influence of the place of residence, smoking and alcohol consumption on bone mineral content in the facial skeleton

Background: Environmental factors exert their influence on the living organism throughout ontogeny. More and more often, researchers find correlations between specific environmental factors and the so-called diseases of affluence. Deficits and excess of essential elements also leave their mark on the skeleton.Aim: To investigate the influence of alcohol consumption, tobacco smoking and place of residence, according to sex and calendar age, on the concentrations of micro-, macro- and toxic elements in human facial bones.Material & methods: Patients undergoing surgical treatment were examined for the mineral content in the collected bone material. The bone contents of the following elements were determined: Ca, K, Mg, Na, P, Fe, Zn, Mo, Ba, Mn, Li, Be, Co, B, Sr, Cr, Pb, Cd, Ni, and Al, depending on the type of facial bone, sex, calendar age, alcohol consumption, tobacco smoking and place of residence.Results: Sex and alcohol consumption showed the highest degree of correlation with the content of the minerals included in the study. Alcohol drinking was found to exert the strongest influence on women’s bodies, the highest number of statistically significant correlations was demonstrated between the content of minerals in the examined bones and alcohol drinking in women. Other factors included in the analysis had a different impact on men and women, the concentrations of elements included in the study differed depending on age, tobacco smoking and place of residence.Conclusions: The observed differences in the element mineral composition of the human facial skeleton may be explained by developmental specifics and functional adaptation. However, general biological characteristics (sex, age), environmental factors (place of residence), as well as smoking and alcohol use may exert significant influence on the concentrations of micro-, macro- and toxic elements in particular regions of the human skeleton. The impact of environmental factors is a very complex phenomenon, which may be stronger or more subtle, leaving its mark on the bone structure. The environmental factors included in the analysis had a different influence on men than women.

Midfacial growth patterns in males from newborn to 5 years old based on computed tomography.

Growth patterns of the human facial skeleton have been of great interest and importance for biological anthropologists, forensic scientists, craniofacial surgeons, and orthopedists. Nevertheless, growth trends of the facial skeleton in infancy and early childhood are still poorly known and clinical CT data have been insufficiently used for studying craniofacial ontogeny. The purpose of this study was to provide a comprehensive quantitative description of human midfacial ontogeny in infancy and early childhood, and to contribute to debates regarding the role of modularity vs. integration in shaping the human face. Our dataset includes 146 high resolution clinical CT datasets of males from the 2nd to 6th years of life and 101 dataset of infants (males) in the 1st year of life. Forty landmarks were collected from each 3D reconstructed skull, then 25 linear measurements describing the morphological features of the facial skeleton were calculated. The integration/modularity issue was addressed via comparison of intragroup correlation matrices at different ages. Growth trends for all the measurements are presented in charts and tables of statistical parameters that can be used as normative data. The midfacial variables display a great diversity of growth patterns. The correlation structure of the measurements is different at different ages. Variables commonly assigned to the same unit of the facial skeleton can exhibit rather different growth trends, but some measurements display seemingly coordinated patterns of growth change. The level of interindividual variation of most measurements is stable after the second half of the first year of life.

Review of In Vivo Bone Strain Studies and Finite Element Models of the Zygomatic Complex in Humans and Nonhuman Primates: Implications for Clinical Research and Practice.

The craniofacial skeleton is often described in the clinical literature as being comprised of vertical bony pillars, which transmit forces from the toothrow to the neurocranium as axial compressive stresses, reinforced transversely by buttresses. Here, we review the literature on bony microarchitecture, in vivo bone strain, and finite-element modeling of the facial skeleton of humans and nonhuman primates to address questions regarding the structural and functional existence of facial pillars and buttresses. Available bone material properties data do not support the existence of pillars and buttresses in humans or Sapajus apella. Deformation regimes in the zygomatic complex emphasize bending and shear, therefore conceptualizing the zygomatic complex of humans or nonhuman primates as a pillar obscures its patterns of stress, strain, and deformation. Human fossil relatives and chimpanzees exhibit strain regimes corroborating the existence of a canine-frontal pillar, but the notion of a zygomatic pillar has no support. The emerging consensus on patterns of strain and deformation in finite element models (FEMs) of the human facial skeleton corroborates hypotheses in the clinical literature regarding zygomatic complex function, and provide new insights into patterns of failure of titanium and resorbable plates in experimental studies. It is suggested that the "pillar and buttress" model of human craniofacial skeleton function be replaced with FEMs that more accurately and precisely represent in vivo function, and which can serve as the basis for future research into implants used in restoration of occlusal function and fracture repair. Anat Rec, 299:1753-1778, 2016. © 2016 Wiley Periodicals, Inc.

Dentofacial changes in adults

The purpose of the present study was to analyze sagittal and vertical cephalometric changes in 41 men and 52 women from 22-43 years of age and to examine differences between the periods 22-33 years (T1-T2) and 33-43 years (T2-T3) as well as gender differences in the changes during the two periods. Our study data derived from three cephalograms of each individual. Very few subjects had undergone orthodontic treatment in childhood, and none had used retainers during the 5 years before the first cephalogram (T1). Neither had any undergone orthodontic treatment or orthognathic surgery during the observation periods. All cephalograms were taken with the same cephalostat, and all subjects were aged between 20 and 26 years, with a mean age of 22.6 and 22.5 years for women and men, respectively, when the first cephalogram was taken. The measurements were taken using a modified Dentofacial Planner SHORT software program. At 22 years of age, all linear parameters (S-N, N-Me, S-tGo, Co-Me, Ar-Me) were larger in men. Of the anteroposterior parameters, S-N increased more in women, while Co-Gn and Ar-Gn increased more in men. This increase was largest in the first period in both genders. The vertical N-Me increased in both genders in both periods, but more in the women. The posterior S-tGo increased more in men in both periods. The lower parts of the vertical parameters increased more than the upper parts. The ML-NSL angle increased during both periods in women, while in men no statistically significant change was revealed. The S-N-A angle decreased in both genders in the first period and continued to decrease in the second in women, while in men an increase in the second period was demonstrated. Angles related to the anteroposterior position of the mandible (S-N-B and S-N-Po) decreased during both periods in women while the angles in men did not change. The incisors retroclined during both periods in both genders. Overall changes were larger in the first period than in the second. Changes of the human facial skeleton continue in the third and forth decade of life and are significant. However, the mandibular growth rate decreases between the third and fourth decade. Men generally have a larger anterior cranial base and a larger face. These gender differences continue to increase with advanced age. The sagittal position of the jaw bases became more retrognathic in women. The reason for the altered mandibular position is also a posterior rotation of the lower jaw. In men, the mandibular inclination remains more stable.

Nasal septal and craniofacial form in European‐ and African‐derived populations

As a component of the chondrocranium, the nasal septum influences the anteroposterior dimensions of the facial skeleton. The role of the septum as a facial growth center, however, has been studied primarily in long-snouted mammals, and its precise influence on human facial growth is not as well understood. Whereas the nasal septum may be important in the anterior growth of the human facial skeleton early in ontogeny, the high incidence of nasal septal deviation in humans suggests the septum's influence on human facial length is limited to the early phases of facial growth. Nevertheless, the nasal septum follows a growth trajectory similar to the facial skeleton and, as such, its prolonged period of growth may influence other aspects of facial development. Using computed tomography scans of living human subjects (n = 70), the goal of the present study is to assess the morphological relationship between the nasal septum and facial skeleton in European- and African-derived populations, which have been shown to exhibit early developmental differences in the nasal septal-premaxillary complex. First we assessed whether there is population variation in the size of the nasal septum in European- and African-derived samples. This included an evaluation of septal deviation and the spatial constraints that influence variation in this condition. Next, we assessed the relationship between nasal septal size and craniofacial shape using multivariate regression techniques. Our results indicate that there is significant population variation in septal size and magnitude of septal deviation, both of which are greater in the European-derived sample. While septal deviation suggests a disjunction between the nasal septum and other components of the facial skeleton, we nevertheless found a significant relationship between the size of the nasal septum and craniofacial shape, which appears to largely be a response to the need to accommodate variation in nasal septal size.

O.313 Finite elements analysis of the human facial skeleton

We computed by a Monte Carlo method derived from the solid on solid model, the thermal relaxation of a polycrystalline thin film deposited on a Penrose lattice. The thin film was modeled by a 2-dimensional array of elementary domains, which have each a given height. During the Monte Carlo process, the height of each of these elementary domains is allowed to change as well as their crystallographic orientation. After equilibrium is reached at a given numerical temperature, all elementary domains have changed their orientation into the same one and small islands appear, preferentially on the domains of the Penrose lattice located in the center of heptagons. This method is a numerical approach to study the influence of the substrate and its defects on the islanding process of polycrystalline films.

A geometric morphometric study of regional differences in the ontogeny of the modern human facial skeleton.

This study examines interpopulation variations in the facial skeleton of 10 modern human populations and places these in an ontogenetic perspective. It aims to establish the extent to which the distinctive features of adult representatives of these populations are present in the early post natal period and to what extent population differences in ontogenetic scaling and allometric trajectories contribute to distinct facial forms. The analyses utilize configurations of facial landmarks and are carried out using geometric morphometric methods. The results of this study show that modern human populations can be distinguished based on facial shape alone, irrespective of age or sex, indicating the early presence of differences. Additionally, some populations have statistically distinct facial ontogenetic trajectories that lead to the development of further differences later in ontogeny. We conclude that population-specific facial morphologies develop principally through distinctions in facial shape probably already present at birth and further accentuated and modified to variable degrees during growth. These findings raise interesting questions regarding the plasticity of facial growth patterns in modern humans. Further, they have important implications in relation to the study of growth in the face of fossil hominins and in relation to the possibility of developing effective discriminant functions for the identification of population affinities of immature facial skeletal material. Such tools would be of value in archaeological, forensic and anthropological applications. The findings of this study underline the need to examine more deeply, and in more detail, the ontogenetic basis of other causes of craniometric variation, such as sexual dimorphism and hominin species differentiation.

Strain pattern in the upper facial skeleton: Preliminary model development

In the human upper facial skeleton, the patterns of strain caused by physiological loading are not known. It is generally accepted that these patterns can be predicted based on the morphology of the bone, but this is not necessarily the case. The elucidation of these patterns of strain has a significant impact on the plating techniques of facial fractures, the development of bone substitutes and tissue-engineered bone, and the understanding of facial development. The goal of this study was to initiate the development of a model that could be used to measure strain magnitude and direction in the upper facial skeleton from physiological loading of facial musculature. A strain gauge was bonded to the lateral orbital rim of a cadaveric skull that had been dissected, leaving only muscular origins and insertions intact. Braided nylon straps were sutured to the origins and insertions of the masseter and levator labii superioris, and these were pulled individually using a hydraulic testing machine. When the masseter origin was pulled, the recorded strain increased with increasing force and the angle of the strain corresponded directly to the angle of pull. When the levator labii superioris origin was pulled, the angle of strain was directed anteriorly and inferiorly, but did not correspond with the axis of the muscle or the axis of the lateral orbital rim where the strain gauge was located. It was concluded that this model is reliable and reproducible for investigating strain magnitude and direction in the human upper facial skeleton.

Craniofacial Distraction Osteogenesis: A Review of 3278 Cases

The nascent field of craniofacial distraction osteogenesis has not yet been subjected to a rigorous evaluation of techniques and outcomes. Consequently, many of the standard approaches to distraction have been borrowed from the experience with long bones in orthopedic surgery. The ideal "latency period" of neutral fixation, rate and rhythm of distraction, and consolidation period have not yet been determined for the human facial skeleton. In addition, because the individual craniofacial surgeon's experience with distraction has generally been small, outcomes and meaningful complication rates have not yet been published. In this study, a four-page questionnaire was sent to 2476 craniofacial and oral/maxillofacial surgeons throughout the world, asking about their experiences with distraction osteogenesis. Information about the types of cases, indications for surgery, surgical techniques, postoperative management, outcomes, and complications were tabulated. Of 274 respondents (response rate, 11.4 percent), 148 indicated that they used distraction in their surgical practice. One hundred forty-five completed surveys were entered into a database that provided information about 3278 craniofacial distraction cases. Statistical analyses were performed comparing the rates of premature consolidation, fibrous nonunion, and nerve injury, on the basis of the use of a latency period and different rates and rhythms of distraction. In addition, the rates of all complications were determined and compared on the basis of the number of distraction cases performed per surgeon. The results of the study clearly show a wide variation in the surgical practice of craniofacial distraction osteogenesis. Although the cumulative complication rate was found to be 35.6 percent, there is a pronounced learning curve, with far fewer complications occurring among more experienced surgeons (p < 0.001). The presence of inferior alveolar nerve injury as a result of mandibular distraction was much lower for respondents whose distraction regimens consisted of no more than 1 mm of distraction per day (19.5 percent versus 2.4 percent; p < 0.001). No evidence was found to support the use of a latency period or to divide the daily distraction regimen into more than one session per day. Conclusions could not be drawn from this study regarding the length of the consolidation period. Overall, the surgeon-reported outcomes are comparable with those published for other craniofacial procedures, despite the higher incidence of complications. Although conclusions made on the basis of a subjective questionnaire need to be interpreted cautiously, this study has strength in the large numbers of cases reviewed. Because of the anonymity of responses, it has been assumed that surgeons who responded to the survey reported accurate numbers of complications and successful outcomes. Finally, additional clinical and animal studies that will be of benefit in advancing the field of craniofacial distraction osteogenesis are outlined.

Biological arches and changes to the curvilinear form of the aging maxilla.

The facial skeleton can be conceptualized as a series of arches aligned along a vertical axis, with regional differences in shape. Previous work suggested that the maxilla undergoes differential growth with time. Because these arch forms resemble geometric forms, it may be possible to measure changes to their shape with the aging process. A contour analysis of the aging maxilla was undertaken. Computed tomographic data were assembled retrospectively. Only men were studied, and they were divided into two groups: young (aged 18 to 24 years; n = 6) and old (aged 40 to 66 years; n = 6). The computed tomography data were reconstructed into three-dimensional images and underwent standardization for comparison purposes. An axial view of the maxilla along the Frankfort horizontal was used for analysis. To quantify changes between curves, measurements were made of the vertical distance from eight equidistant points along each curve perimeter to a standardized baseline. Average arch forms for young and old men were then generated for comparison purposes. Each of the eight points along the older maxillary arch form existed further from the baseline than the younger arch form. This difference reached statistical significance at three of the eight points measured along the two curves. The greatest difference occurred at point 8 (p = .0006), which was at the medial maxilla near the nasomaxillary junction. The results of the study suggest that the actual contour of the maxilla undergoes changes as a result of the aging process. Mathematically defined idealized skeletal contours could help guide reconstructive surgery and aesthetic augmentation of the facial skeleton in the future. In addition, certain soft tissues of the face and torso seem to share a common shape (an alpha contour). This shape may also exhibit idealized forms open to quantitative analysis. The skeletal arch form and alpha contour most likely exhibit sexual dimorphism and will require further investigation. The ubiquity of the arch form in nature and possible implications for growth and development of the human facial skeleton are also discussed.

Human facial tolerance to steering wheel impact: A biomechanical study

In an effort to delineate the tolerance of the human facial skeleton with respect to steering wheel impact, research was conducted using human cadavers. We reported the biodynamics of steering-wheel-induced facial trauma due to impacts at the unsupported rim (Yoganandan, Pintar & Sances, 1991). The present study was conducted to determine the probability of facial bone fracture secondary to impact at the spoke-rim junction. Either zygoma was impacted once onto the spoke-rim junction at velocities ranging from 1.4–6.9 m s . A six-axis load cell placed under the hub documented the generalized force histories. Interface force at the impact location was computed using the generalized force and deformation histories recorded at the spoke-rim junction using transformation principles. Bone mineral content was also determined. Facial pathology was evaluated using x-ray, two- and three-dimensional computed tomography, and defleshed skulls. Fractures of the zygoma, orbit, and maxilla were observed. While higher impact velocities resulted in propagation of fracture to the contralateral site, unilateral fractures of less severity occurred at lower speeds. Results indicated that a force level of 1525 N corresponds to 50% probability of facial fracture for the spoke-rim junction. Consequently, significant amelioration of facial injuries can be achieved if the forces are kept below this limit.

A personalized finite element model for the study of boston brace correction in idiopathic scoliosis

In an effort to delineate the tolerance of the human facial skeleton with respect to steering wheel impact, research was conducted using human cadavers. We reported the biodynamics of steering-wheel-induced facial trauma due to impacts at the unsupported rim (Yoganandan, Pintar & Sances, 1991). The present study was conducted to determine the probability of facial bone fracture secondary to impact at the spoke-rim junction. Either zygoma was impacted once onto the spoke-rim junction at velocities ranging from 1.4–6.9 ms. A six-axis load cell placed under the hub documented the generalized force histories. Interface force at the impact location was computed using the generalized force and deformation histories recorded at the spoke-rim junction using transformation principles. Bone mineral content was also determined. Facial pathology was evaluated using x-ray, two- and three-dimensional computed tomography, and defleshed skulls. Fractures of the zygoma, orbit, and maxilla were observed. While higher impact velocities resulted in propagation of fracture to the contralateral site, unilateral fractures of less severity occurred at lower speeds. Results indicated that a force level of 1525 N corresponds to 50% probability of facial fracture for the spoke-rim junction. Consequently, significant amelioration of facial injuries can be achieved if the forces are kept below this limit.

Biomechanical Simulation Study on the Forms of the Frontal Bone and Facial Bones of the Recent Human Facial Skeleton by Using a Two-Dimensional Frame Model with Stepwise Variable Cross-Section Members

The form in frontal view of the recent human facial skeleton, including the frontal bone, was simulated under the condition of uniform strength to cope with the forces in the chewing action, by using the two-dimensional frame model made of members with step-wise variable cross-sections and by using the finite element analysis method. The simulation, in which the condition was applied to the elements of the model in the frontal bone region, resulted in a form different from the actual facial skeleton But the simulation in which the condition was not applied to the above elements resulted in a form tolerably similar to the actual facial skeleton. Hence, it was concluded that the biomechanical role of the frontal bone was different from that of the facial bones: the former was part of the brain casing and the latter a chewing machine, including the casings of the eyes and the nose, regulated by the law of uniform strength to cope with the forces in the chewing action.

Stress analysis on the facial skeleton of gorilla by means of the wire strain gauge method

Simulation of the biting action of the gorilla was made by using a macerated skull of the gorilla. Strains in the facial skeleton produced by this simulation were measured by the wire strain gauge. Some stress analyses were made from these strains and were compared with those of the human facial skeleton. The strains in the facial skeleton of the gorilla indicate fundamentally the same deformation during biting action as do those of the human facial skeleton, but differences between both facial skeletons also appear. Generally the force of the temporalis tends to strain the facial skeleton more compressively while the force of the masseter does so more tensilely. They produce qualitatively the same but quantitatively different strains or stresses.

A comparative study of facial growth in Homo and Macaca.

AbstractSections were prepared throughout all areas of the various facial bones in young, growing Rhesus monkeys. The detailed distribution of resorptive and depository surfaces and the distribution of endosteal and periosteal bone tissue types were determined. From this information, the sequence of remodeling changes associated with the growth of the facial skeleton was then interpreted. This study is a sequal to previous reports in which growth and remodeling processes in the human face were described using similar procedures. In the present report, growth changes in the monkey and human facial skeleton are compared and contrasted. The general plan of facial growth is similar in both species, but major differences exist in the area of the muzzle. The maxillary arch in the monkey is entirely depository in nature, and it grows in a forward and downward direction as the maxillary tuberosity simultaneously grows backward. In the human, the forward part of the maxillary arch is resorptive in character. This contrasting growth factor results in a downward but not forward movement of this area. The result is decreased prognathism. Other differences in growth pattern exist in the forehead, malar, chin, and orbit. The developmental and phylogenetic basis for the upright human face is discussed and evaluated.