A study of sutural bones in Gujarati (Indian) crania

370 adult crania were examined to find the incidence of sutural bones in Gujarati (Indian) crania and to compare it with other populations to establish the distance between them. The mean measure of difference between Indian and other populations was statistically significant. Comparison of cranial capacity in skulls with and without sutural bones showed no significant difference, and this is interpreted as indicating that sutural bones are not formed secondary to stress.     

A study of sutural bones in different morphological forms of skulls

117 adult human skulls were classified for three morphological forms, i.e. dolichocephalic, mesocephalic and brachycephalic, and were examined for the presence of sutural bones in each form. Sutural bones occur in each forms of the skulls with no statistically significant differences. This finding is interpreted as indicating that sutural bones are not formed secondary to stress, otherwise the incidence of the sutural bones would have been differed in different morphological forms of skulls.     

Sutural bone frequency in synostotic rabbit crania

This study tests the hypothesis that crania with synostosed sutures will have a significantly higher incidence of calvarial sutural bones than normal crania. Sutural bones were counted in seven calvarial sutures and compared among four groups of adult New Zealand white rabbit skulls: normal in-colony (NI) controls (N = 14), normal out-colony (NO) controls (N = 12), skulls with familial delayed onset (DO) coronal synostosis (N = 25), and skulls with experimentally immobilized coronal sutures (EI) (N = 20). Comparisons among groups were made with a Kruskal-Wallis one-way ANOVA and between groups with a Mann-Whitney U-test, using a Bonferroni correction for multiple comparisons. Significant differences (P > 0.05) were noted only in the coronal and sagittal sutures, with EI crania having the greatest number of coronal sutural bones; between group differences were undetectable for sagittal sutural bones. A post hoc two-sample binomial test for equal proportions showed that the distribution of coronal sutural bones among individuals across groups was even, while the distribution of sagittal sutural bones was significantly higher in EI crania. These results suggest that altered sutural forces of the calvaria contribute to an increased occurrence of sutural bones. However, the influence of inheritance on increased occurrence of sutural bones cannot be discounted, as reflected in the equivalent number of individuals across groups that possessed coronal sutural bones. Am J Phys Anthropol 102:555–563, 1997. © 1997 Wiley-Liss, Inc.     

Sutural complexity in artificially deformed human (Homo sapiens) crania.

The pattern of complexity of cranial sutures is highly variable both among and within species. Intentional cranial vault deformation in human populations provides a controlled natural experiment by which we were able to quantify aspects of sutural complexity and examine the relationship between sutural patterns and mechanical loading. Measures of sutural complexity (interdigitation, number, and size of sutural bones) were quantified from digitized tracings of 13 sutures and compared among three groups of crania (n = 70) from pre-European contact Peru. These groups represent sample populations deformed in 1) anteroposterior (AP) and 2) circumferential (C) directions and 3) an undeformed population. Intergroup comparisons show few differences in degree or asymmetry of sutural interdigitation. In the few comparisons which show differences, the C group is always more interdigitated than the other two while the AP group has more sutural bones. The sutures surrounding the temporal bone (sphenotemporal, occipitotemporal, and temporoparietal) most frequently show significant differences among groups. These differences are related to the more extreme binding of C type deformation and are consistent with hypothesized increases in tension at coronally oriented sutures in this group. The larger number of sutural bones in the AP group is consistent with the general broadening of the cranium in this group and with experimental evidence indicating the development of ossicles in areas of tension. We suggest that so few changes in sutural complexity occurred either because the magnitude of the growth vectors, unlike their direction, is not substantially altered or because mechanisms other than sutural growth modification are responsible for producing the altered vault shapes. In addition, the presence of fontanelles in the infant skulls during binding and the static nature of the binding may have contributed to the similarity in complexity among groups.     

Effects of different kinds of cranial deformation on the incidence of wormian bones

Researchers have debated whether the presence and frequency of wormian bones (sutural bones, supernumerary bones, and ossicles) are attributable to genetic factors, environmental factors, or both. This research examines the effects of many different kinds of cranial deformation on the incidence of wormian bones. A sample of 127 deformed and undeformed crania from New World archaeological sites was examined. An undeformed cranial sample (n=35) was compared to the following cranially deformed groups: 1) occipital, 2) lambdoid, 3) annular, 4) fronto-vertico-occipital, 5) parallelo-fronto-occipital, and 6) sagittal synostosis. Three levels of degree of cultural cranial deformation were qualitatively determined. Type and number of wormian bones along each major suture were recorded for each cranium. Group means were analyzed using Kruskal-Wallis one-way ANOVA statistical tests to test the null hypothesis that cranial deformation does not have an effect on wormian bone incidence. Results indicate that all forms of cranial deformation affect the frequency of some types of wormian bones. In particular, all cranially deformed groups exhibited significantly greater frequencies of lambdoid ossicles. Apical, parieto-mastoid, and occipito-mastoid wormian bones also appeared with greater frequency in some groups of culturally deformed crania. Further, varying degrees of cultural deformation all had more lambdoid wormian bones than the undeformed group. These results suggest that wormian bone development in posteriorly placed sutures may be affected more by environmental forces than are their anteriorly placed counterparts.     

Mechanical properties of cranial sutures

Many bones in mammalian skulls are linked together by cranial sutures, connective tissue joints that are morphologically variable and show different levels of interdigitation among and within species. The goal of this investigation was to determine whether sections of skull with cranial sutures have different mechanical properties than adjacent sections without sutures, and if these properties are enhanced with increased interdigitation. To test these hypotheses, bending strength and impact energy absorption were measured for samples of goat (Capra hircus) cranial bone without sutures and with sutures of different degrees of interdigitation. Bending strength was measured under both dynamic (9.7 mm displacement s-1) and relatively static (0.8 mm s-1) conditions, and at either speed, increased sutural interdigitation provided increased strength during three-point bending. However, except for very highly interdigitated sutures loaded slowly, sutures were not as strong in bending as bone. In contrast, sutures absorbed from 16% to 100% more energy per unit volume during impact loading than did bone. This five-fold increase in energy absorption by the sutures was significantly correlated with increased sutural interdigitation.     

Multi-dimensional complexes of skull traits

The simultaneous incidence of sutural bones was studied by a multidimensional analysis (Wanke method). On a medieval sample of 249 male and female skulls from Lower Austria the presence of two main complexes of sutural and fontanelle bones was observed. The interaction of possible genetic factors and developmental growth incongruences in causing these phenomena are discussed. The necessity of further studies considering such basic biological aspects with minor skeletal traits is stressed.     

Jaw muscles and the skull in mammals: the biomechanics of mastication.

Among non-mammalian vertebrates, rigid skulls with tight sutural junctions are associated with high levels of cranial loading. The rigid skulls of mammals presumably act to resist the stresses of mastication. The pig, Sus scrofa, is a generalized ungulate with a diet rich in resistant foods. This report synthesizes previous work using strain gages bonded to the bones and sutures of the braincase, zygomatic arch, jaw joint, and mandible with new studies on the maxilla. Strains were recorded during unrestrained mastication and/or in anesthetized pigs during muscle stimulation. Bone strains were 100-1000 micro epsilon, except in the braincase, but sutural strains were higher, regardless of region. Strain regimes were specific to different regions, indicating that theoretical treatment of the skull as a unitary structure is probably incorrect. Muscle contraction, especially the masseter, caused strain patterns by four mechanisms: (1) direct loading of muscle attachment areas; (2) a compressive reaction force at the jaw joint; (3) bite force loading on the snout and mandible; and (4) movement causing new points of contact between mandible and cranium. Some expected patterns of loading were not seen. Most notably, strains did not differ for right and left chewing, perhaps because pigs have bilateral occlusion and masseter activity.     

Remodeling of the sagittal suture in osteopetrotic (op/op) mice associated with cranial flat bone growth.

It is well known that cranial flat bone experiences growth and development at the sutural interface, which is regarded as a neutral zone to control mechanical stimuli. In osteopetrotic (op/op) mice, meanwhile, cranial deformation is produced by the deficiency of osteoclasts and the subsequent defect of bone resorption. It would be a reasonable assumption that such disturbance in bone remodeling affects sutural modification and the relevant cranial flat bone development. The present study was thus conducted to examine histological features of the sagittal sutures in op/op mice, with special reference to the relevant bone remodeling. The sagittal sutures in 10-, 15-, 30-, and 60-day-old normal and op/op mice were observed microscopically. Furthermore, osteoclastic activity was evaluated on the sections stained with tartrate-resistant acid phosphatase (TRAP). The sutures of 15-day-old op/op mice showed stenosis and synostosis, and less-developed collagen fibers associated with an irregular arrangement of fibroblasts, whereas these changes were rarely found in normal mice. Osteoclasts were hardly detected in the parietal bones around the sutures of op/op mice, although the number was numerous in normal mice. These results emphasize that congenital deficiency in osteoclast produces unbalanced bone remodeling at the sutural interface and on the surfaces of the cranial bones, which is assumed to be closely related to cranial bone deformity in op/op mice.     

Studies on the skull of the Indian sisorid catfish, Erethistes pussilus

The skull of Erethistes pussilus is described in detail. The general disposition of the bones corresponds to the siluroid pattern. Among the siluroid fishes, E. pussilus approaches the advanced forms in certain features such as obliteration of myodomic space, edentulous palate, absence of entopterygoids and supratemporals, intimate sutural articulation of posttemporals and complex vertebra with the cranium, diminished cranial cavity and loss of sutural articulation among the palatopterygoquadrate elements. In certain characters like the hyomandibula exclusively supported from the sphenotic, solitary hypohyal on each hyoid cornu, absence of interhyals, reduced orbits, edentulous vomer, small gape of mouth, toothless ectopterygoid and in the small number of branchiostegals, E. pussilus stands specialized alone among the catfishes. A diagnosis of the salient cranial characters of the fish is given and its relationship discussed.     

Studies on the skull of the Indian sisorid catfish, Erethistes pussilus

The skull of Erethistes pussilus is described in detail. The general disposition of the bones corresponds to the siluroid pattern. Among the siluroid fishes, E. pussilus approaches the advanced forms in certain features such as obliteration of myodomic space, edentulous palate, absence of entopterygoids and supratemporals, intimate sutural articulation of posttemporals and complex vertebra with the cranium, diminished cranial cavity and loss of sutural articulation among the palatopterygoquadrate elements. In certain characters like the hyomandibula exclusively supported from the sphenotic, solitary hypohyal on each hyoid cornu, absence of interhyals, reduced orbits, edentulous vomer, small gape of mouth, toothless ectopterygoid and in the small number of branchiostegals, E. pussilus stands specialized alone among the catfishes. A diagnosis of the salient cranial characters of the fish is given and its relationship discussed.     

Fusion patterns of craniofacial sutures in rhesus monkey skulls of known age and sex from Cayo Santiago

Bones of the face and cranial vault meet at sutural boundaries. These sutures are of great importance for craniofacial growth. Although the effects that the sutures have on modulating craniofacial strains have been investigated, how sutural fusion influences primate craniofacial biomechanics and adaptation are less considered. Confounding this problem is the lack of any systematic data on patterns of craniofacial sutural fusion from animals of known age and sex. This study examined the status of 28 sutures in Macaca mulatta skulls from a collection of animals of known age and sex from Cayo Santiago, Puerto Rico. Survival analysis showed that most animals died before all sutures fused. There was high variation in the age at which individual sutures or sutural sections were fused in M. mulatta, and significant differences in the amount of sutural fusion among regions and between males and females. Intensive fusion of sutures took place between ages 5 and 15. Sutures in the facial area tended to be less fused than in the cranial vault. Between adolescence and adulthood, males tended to have more sutural fusion than females, especially in the facial area. These differences might be biomechanical adaptations during ontogeny to craniofacial sexual dimorphism. These findings enrich our understanding of variation in sutural morphology in rhesus monkeys. Comparative information across primate species is essential for understanding the biomechanics of craniofacial form throughout primate evolution.     

Size and shape of human cranial sutures--a new scoring method

A method for the differentiation of sutural patterns of the human cranial vault is introduced. Three criteria of differentiation are considered, one for size and two for shape: 1) maximal shape extension; 2) basic configuration; 3) secondary protrusion. The method is illustrated here for the coronal and lambdoid sutures of 70 recent Italian skulls (35 adult males and 35 adult females). Differences between coronal and lambdoid sutural size and shape can be detected analytically; for example, the coronal suture commonly shows lesser degrees of shape extension, a simpler basic configuration, and an absence of secondary protrusion. Heterogeneity within each suture, as well as a relationship among corresponding sections and between the three criteria adopted, have been also observed; symmetry predominates for both the sutures, and sexual differences are slight.     

Fusion Patterns in the Skulls of Modern Archosaurs Reveal That Sutures Are Ambiguous Maturity Indicators for the Dinosauria

The sutures of the skulls of vertebrates are generally open early in life and slowly close as maturity is attained. The assumption that all vertebrates follow this pattern of progressive sutural closure has been used to assess maturity in the fossil remains of non-avian dinosaurs. Here, we test this assumption in two members of the Extant Phylogenetic Bracket of the Dinosauria, the emu, Dromaius novaehollandiae and the American alligator, Alligator mississippiensis, by investigating the sequence and timing of sutural fusion in their skulls. As expected, almost all the sutures in the emu skull progressively close (i.e., they get narrower) and then obliterate during ontogeny. However, in the American alligator, only two sutures out of 36 obliterate completely and they do so during embryonic development. Surprisingly, as maturity progresses, many sutures of alligators become wider in large individuals compared to younger, smaller individuals. Histological and histomorphometric analyses on two sutures and one synchondrosis in an ontogenetic series of American alligator confirmed our morphological observations. This pattern of sutural widening might reflect feeding biomechanics and dietary changes through ontogeny. Our findings show that progressive sutural closure is not always observed in extant archosaurs, and therefore suggest that cranial sutural fusion is an ambiguous proxy for assessing maturity in non-avian dinosaurs.     

Skull deformations in craniosynostosis and endocrine disorders: Morphological and tomographic analysis of the skull from the crypt of the Silesian Piasts in Brzeg (16th–17th century), Poland

Results

of morphological and tomographic (CT) studies of the skull that was found in the crypt of the Silesian Piasts in the St. Jadwiga church in Brzeg (Silesia, Poland) are presented and discussed here. The established date of burial of probably a 20–30 years old male was 16th–17th century. The analyzed skull showed premature obliteration of the major skull sutures. It resulted in the braincase deformation, similar to the forms found in oxycephaly and microcephaly. Tomographic analysis revealed gross pathology. Signs of increased intracranial pressure, basilar invagination and hypoplasia of the occipital bone were observed. Those results suggested the occurrence of the very rare Arnold-Chiari syndrome. Lesions found in the sella turcica indicated the development of pituitary macroadenoma, which resulted in the occurrence of discreet features of acromegaly in the facial bones. The studied skull was characterized by a significantly smaller size of the neurocranium (horizontal circumference 471 mm, cranial capacity ∼1080 ml) and strongly expressed brachycephaly (cranial index = 86.3), while its height remained within the range for non-deformed skulls. A narrow face, high eye-sockets and prognathism were also observed. Signs of alveolar process hypertrophy with rotation and displacement of the teeth were noted. The skull showed significant morphological differences compared to both normal and other pathological skulls such as those with pituitary gigantism, scaphocephaly and microcephaly.     

Paleoclimatic Variation and Brain Expansion during Human Evolution

One of the major adaptations during the evolution of Homo sapiens was an increase in brain size. Here we present evidence that a significant and substantial proportion of variation in brain size may be related to changes in temperature. Based on a sample of 109 fossilized hominid skulls, we found that cranial capacities were highly correlated with paleoclimatic changes in temperature, as indexed by oxygen isotope data and sea-surface temperature. Indeed, as much as 52% of the variance in the cranial capacity of these skulls could be accounted for by temperature variation at 100 ka intervals. As an index of more short-term seasonal fluctuations in temperature, we examined the latitude of the sites from which the crania originated. More than 22% of the variance in cranial capacity of these skulls could be accounted for by variation in equatorial distance.     

Geometrical and material parameters to assess the macroscopic mechanical behaviour of fresh cranial bone samples

The present study aims at providing quantitative data for the personalisation of geometrical and mechanical characteristics of the adult cranial bone to be applied to head FE models. A set of 351 cranial bone samples, harvested from 21 human skulls, were submitted to three-point bending tests at 10 mm/min. For each of them, an apparent elastic modulus was calculated using the beam's theory and a density-dependant beam inertia. Thicknesses, apparent densities and percentage of ash weight were also measured. Distributions of characteristics among the different skull bones show their symmetry and their significant differences between skull areas. A data analysis was performed to analyse potential relationship between thicknesses, densities and the apparent elastic modulus. A specific regression was pointed out to estimate apparent elastic modulus from the product of thickness by apparent density. These results offer quantitative tools in view of personalising head FE models and thus improve definition of local injury criteria for this body part.     

Cranial ontogeny of otariid seals

Over 2000 otariid skulls were measured for a morphometric study of cranial ontogeny in fur seals and sea lions. Few interspecific differences in cranial ontogeny were observed in the Otariidae, with only minor differences in rates of growth. Sexual dimorphism was significant in all otariids but was more apparent in the larger species. Female otariids of each species showed monophasic development in all characteristics, whereas males expressed monophasic growth for some characters and biphasic growth for others. Biphasic development in skulls of male otariids occurred well after physical maturity had been reached, usually at a suture index of 27. The rate of development varied between skull characters; components relating to the nervous system completed growth well before the rest of the skull, whereas those related to feeding, respiration and vocalisation developed in synchrony with the overall growth of total skull length. Sutures of the calvaria, or braincase, were the first to show partial closure and those uniting the facial bones were usually the last to fuse. As with the calvaria, the orbits and otic capsules developed quickly, suggesting a need for good hearing and vision early in independent postnatal life. Development of the rostral and palatal regions required significantly longer to complete growth.