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Cranial sutures are fibrous connective tissue articulations found between intramembranous bones of the vertebrate cranium. Growth and remodeling of these tissues is partially regulated by biomechanical loading patterns that include stresses related to chewing. Advances in oral processing structure and function of the cranium that enabled mammalian‐style chewing is commonly tied to the origins and evolution of this group. To what degree masticatory overuse or underuse shapes the complexity and ossification around these articulations can be predicted based on prior experimental and comparative work. Here, we report on a mouse model system that has been used to experimentally manipulate dietary material properties in order to investigate cranial suture morphology. Experimental groups were fed diets of contrasting material properties. A masticatory overuse group was fed pelleted rodent chow, nuts with shells, and given access to cotton bedding squares. An underuse group was deprived of cotton bedding as well as diverse textured food, and instead received gelatinized food continuously. Animals were raised from weaning to adulthood on these diets, and sagittal, coronal and lambdoid suture morphology was compared between groups. Predicted intergroup variation was observed in mandibular corpus size and calvarial suture morphology, suggesting that masticatory overuse is associated with jaw and suture growth. The anterior region of the sagittal suture where it intersects with the coronal suture (bregma) showed no effect from the experiment. The posterior sagittal suture where it intersects with the lambdoid sutures (lambda) was more complex in the overuse group. In other words, the posterior calvarium was responsive to dietary material property demands while the anterior calvarium was not. This probably resulted from the different strain magnitudes and/or strain frequencies that occurred during overuse diets with diverse material properties as compared with underuse diets deprived of such enrichment. This work highlights the contrasting pattern of the sutural response to loading differences within the calvarium as a result of diet. [ABSTRACT FROM AUTHOR]

The orbits and eyes of modern humans are situated directly below the frontal lobes and anterior to the temporal lobes. Contiguity between these orbital and cerebral elements could generate spatial constraints, and potentially lead to deformation of the eye and reduced visual acuity during development. In this shape analysis we evaluate whether and to what extent covariation exists between ocular morphology and the size and spatial position of the frontal and temporal areas in adult modern humans. Magnetic resonance imaging (MRI) was used to investigate patterns of variation among the brain and eyes, while computed tomography (CT) was used to compare cranial morphology in this anatomical region among modern humans, extinct hominids and chimpanzees. Seventeen landmarks and semi-landmarks that capture the outline of the eye, frontal lobe, anterior fossa/orbital roof and the position of the temporal tips were sampled using lateral scout views in two dimensions, after projection of the average grayscale values of each hemisphere, with midsagittal and parasagittal elements overlapped onto the same plane. MRI results demonstrated that eye position in adult humans varies most with regard to its horizontal distance from the temporal lobes and, secondly, in its vertical distance from the frontal lobes. Size was mainly found to covary with the distance between the eye and temporal lobes. Proximity to these cerebral lobes may generate spatial constraints, as some ocular deformation was observed. Considering the CT analysis, modern humans vary most with regard to the orientation of the orbits, while interspecific variation is mainly associated with separation between the orbits and endocranial elements. These findings suggest that size and position of the frontal and temporal lobes can affect eye and orbit morphology, though potential effects on eye shape require further study. In particular, possible effects of these spatial and allometric relationships on the eye and vision should be examined using ontogenetic samples, vision parameters such as refractive error in diopters, and three-dimensional approaches that include measures of extraocular soft tissues within the orbit. [ABSTRACT FROM AUTHOR]

Midsagittal cerebral morphology provides a homologous geometrical reference for brain shape and cortical vs. subcortical spatial relationships. In this study, midsagittal brain shape variation is investigated in a sample of 102 humans, in order to describe and quantify the major patterns of correlation between morphological features, the effect of size and sex on general anatomy, and the degree of integration between different cortical and subcortical areas. The only evident pattern of covariation was associated with fronto-parietal cortical bulging. The allometric component was weak for the cortical profile, but more robust for the posterior subcortical areas. Apparent sex differences were evidenced in size but not in brain shape. Cortical and subcortical elements displayed scarcely integrated changes, suggesting a modular separation between these two areas. However, a certain correlation was found between posterior subcortical and parietal cortical variations. These results should be directly integrated with information ranging from functional craniology to wiring organization, and with hypotheses linking brain shape and the mechanical properties of neurons during morphogenesis. [ABSTRACT FROM AUTHOR]

According to the classical theory, teeth derive from odontodes that invaded the oral cavity in conjunction with the origin of jaws (the ‘outside in’ theory). A recent alternative hypothesis suggests that teeth evolved prior to the origin of jaws as endodermal derivatives (the ‘inside out’ hypothesis). We compare the two theories in the light of current data and propose a third scenario, a revised ‘outside in’ hypothesis. We suggest that teeth may have arisen before the origin of jaws, as a result of competent, odontode-forming ectoderm invading the oropharyngeal cavity through the mouth as well as through the gill slits, interacting with neural crest-derived mesenchyme. This hypothesis revives the homology between skin denticles (odontodes) and teeth. Our hypothesis is based on (1) the assumption that endoderm alone, together with neural crest, cannot form teeth; (2) the observation that pharyngeal teeth are present only in species known to possess gill slits, and disappear from the pharyngeal region in early tetrapods concomitant with the closure of gill slits, and (3) the observation that the dental lamina ( sensu  Reif, 1982 ) is not a prerequisite for teeth to form. We next discuss the progress that has been made to understand the spatially restricted loss of teeth from certain arches, and the many questions that remain regarding the ontogenetic loss of teeth in specific taxa. The recent advances that have been made in our knowledge on the molecular control of tooth formation in non-mammalians (mostly in some teleost model species) will undoubtedly contribute to answering these questions in the coming years. [ABSTRACT FROM AUTHOR]

The aim of the present study was to discover how intergenerational undernutrition affects the growth of major and minor functional cranial components in two generations of rats. Control animals constituted the parental generation (P). The undernourished generations (F1 and F2) were fed 75% of the control diet. Animals were X-rayed every 10 days from 20 to 100 days of age. The length, width and height of the major (neurocranium and splanchnocranium) and minor (anterior-neural, middle-neural, posterior-neural, otic, respiratory, masticatory and alveolar) cranial components were measured on each radiograph. Volumetric indices were calculated to estimate size variations of these components. Data were processed using the Kruskal–Wallis and Kolmogorov–Smirnov tests for two samples. Impairment in splanchnocranial and neurocranial growth was found, the latter being more affected than the former in F1. Comparison between F2 and F1 animals showed cumulative effects of undernutrition in both major and minor components (anterior-neural, respiratory, masticatory and alveolar in males, and middle-neural and respiratory in females). Such differential effects on minor components may reflect a residual mechanical strain resulting from the linkage between components. This phenomenon was clearly observed in the neurocranium and could be understood as an adaptive response to the demands of the associated functional matrices. [ABSTRACT FROM AUTHOR]

Cranial sutures are the growth centres of the skull, enabling expansion of the skull to accommodate rapid growth of the brain. Haploinsufficiency of the humanTWISTgene function causes the craniosynostosis syndrome, Saethre–Chotzen syndrome (SCS), in which premature fusion of the coronal suture is a characteristic feature. Previous studies have indicated thatTwistis expressed in the coronal suture during development, and therefore that it may play an important role in development and maintenance of the suture. TheTwist-null mouse is lethal before the onset of osteogenesis, and the heterozygote exhibits coronal suture synostosis postnatally. In this study we investigated the function of Twist in the development of the mouse coronal suture, by inhibiting Twist synthesis using morpholino antisense oligonucleotides in calvarial organ culture. Decreased Twist production resulted in a narrow sutural space and fusion of bone domains within 48 h after the addition of the morpholino oligonucleotides. Proliferation activity in the sutural cells was decreased, and the expression of osteogenic marker genes such asRunx2andFgfr2was up-regulated in the developing bone domain within 4 h. These results suggest that during establishment of the suture area, Twist is required for the regulation of sutural cell proliferation and osteoblast differentiation. [ABSTRACT FROM AUTHOR]

A/WySnJ mice are an inbred strain that develops cleft lip with or without cleft palate (CL/P) with a frequency of 25–30% and a predominantly unilateral expression pattern. As in humans, the pattern of incomplete penetrance, and variable and frequent unilateral expression suggests a role for altered regulation of variability (developmental stability, canalization and developmental integration) during growth. We compared both mean and variability parameters for craniofacial shape and size among A/WySnJ mice, a strain that does not develop CL/P (C57BL/6J) and their F1 cross. We show that adult A/WySnJ mice that do not express cleft lip exhibit decreased morphological integration of the cranium and that the co-ordination of overall shape and size variation is disrupted compared with both C57BL/6J mice and the F1 cross. The decrease in integration is most pronounced in the palate and face. The absence of this pattern in the F1 cross suggests that it is determined by recessive genetic factors. By contrast, the shape differences between the strains, which are thought to predispose A/WySnJ mice to CL/P, show a range of dominance which suggests a polygenic basis. We suggest that decreased integration of craniofacial growth may be an aetiological factor for CL/P in A/WySnJ mice. [ABSTRACT FROM AUTHOR]

The three dimensional co-ordinates of a large number of landmarks on a series of Polynesian skulls have been obtained by means of a diagraph, and from standard lateral cephalograms. The method is accurate, and a very large amount of data is stored in the concise form of the standardized co-ordinates. A factor analysis of some of these data defines a number of distinct craniofacial segments showing independent variation in positioning, and therefore presumably growth, along defined axes. The segments thus defined relate well to the conclusions of other studies of skull growth and form, and support the view that the basis of cranial variation is the same for all Homo sapiens. It is suggested that the strict independence of the isolated craniofacial segments may be a consequence of the particular method, and may not truly reflect the situation in the growing skull.