Natural variations in cochlear anatomy have substantial implications for both clinical care and research in the fields of otology, neurotology, and audiology. While precise anatomic characterization is essential for a multitude of applications, comprehensive reference dimensions of both osseous and membranous cochlear structure obtained from a large and morphologically heterogeneous sample set do not currently exist. In this study, one hundred healthy human cadaveric temporal bone samples, without historical or visible pathology, underwent high-resolution three-dimensional synchrotron radiation phase-contrast imaging (SR-PCI) to develop a morphometric compendium of the human cochlea. Measurements of both bone and soft tissue in the cochlea were obtained, including basal turn diameter and width, cochlear height, and cochlear length along multiple anatomic paths (lateral wall, basilar membrane, and modiolar wall). The hook region, scalar geometry (diameter, area, tilt, width, and volume), and round window dimensions were also comprehensively characterized. Normative tonotopic frequency distributions of the basilar membrane and spiral ganglion were derived using cochlear length measurements and Greenwood's frequency-position function. These anatomic benchmarks establish invaluable reference data which may be used for anatomically informed, precision medicine approaches, including patient-specific surgical planning, intracochlear pharmaceutical delivery optimization, the development of automated image analysis algorithms, and the investigation of cochlear structure-function relationships in pathological conditions.

Climate highly influenced the distribution of major animal groups that emerged during the Triassic throughout the supercontinent Pangea. The earliest dinosaurs and associated assemblages (Carnian Stage, Late Triassic, ~230 Ma) are recovered along a paleolatitudinal climate belt spanning southern Pangea. However, developmental responses of different amniotic clades to climate across these environments remain unknown. Characterizing developmental variability, presumably driven in part by climatic variability within this belt, helps constrain the climatic ranges that shaped the earliest dinosaurs prior to their worldwide dispersal, while also providing insights into developmental plasticity of Triassic fauna. We analyzed the bone histology of five vertebrate taxa from the Carnian of Zimbabwe, including sauropodomorph and herrerasaurid dinosaurs, a gomphodontosuchine cynodont, a hyperodapedontine rhynchosaur, and a suchian archosaur (?aetosaur) as a proxy to assess probable climatic influence by comparing various growth strategies/metabolisms of these clades across southern Pangea. The dinosaurs are continuously growing individuals that exhibit well-vascularized woven-parallel and parallel-fibered cortical bone with no apparent growth marks. The cynodont is an immature specimen with a well-vascularized fibrolamellar matrix that has anastomosing vascular canals throughout the cortex and a single growth mark, indicating rapid growth. The rhynchosaurian femur and suchian tibia show moderate to poorly vascularized parallel-fibered and woven-fibered matrixes possessing multiple lines of arrested growth along with an external fundamental system, suggesting these were slow-growing individuals that had reached skeletal maturity at the time of death. Comparing this histology to that of similar assemblages from current-day Brazil, Argentina, and India (which fell along the same paleolatitudinal zone during the Triassic), the mid-continent (i.e., Zimbabwean) dinosaurs exhibit continuous uninterrupted growth in contrast to other histologically sampled dinosaurs from different localities along this climatic belt, whereas the Zimbabwean rhynchosaur and suchian exhibit patterns with more frequent cessation of growth than their South American counterparts. Slower-growing Zimbabwean taxa-presumably, more susceptible to climatic stressors-exhibit characteristics suggestive of a less resource-rich environment (e.g., frequent cessations, more interrupted growth) compared with rhynchosaurs and aetosaurs from South America. Taxa with faster growth rates and higher metabolic regimes (i.e., dinosaurs, cynodont) from this same assemblage apparently grew rapidly-and roughly continuously-throughout the year. This is consistent with an overall more arid but less seasonal climate in Zimbabwe compared to the signals recovered in Brazil, Argentina, and India.

Epithelial thickness, depth of the ciliary layer and concentration of cells has been estimated at 5 levels of the rat airway (3 extrapulmonary and 2 intrapulmonary) and the ultrastructure of the cells described. Extrapulmonary airways have a pseudostratified epithelium, intrapulmonary airways a simple one. The epithelium thins progressively from upper to lower trachea while the epithelium of the lower trachea is thicker than at more peripheral airway levels, all of which are similar. The depth of the ciliary layer decreases peripherally. By electron microscopy 10 cell types could be identified - 8 epithelial and 2 'migratory'. A cell type not described previously has been found that resembles the serous cells of the submucosal glands. The salient features of each cell type are described. The upper trachea has a concentration of cells significantly higher than elsewhere, while the remaining four airway levels have about 230 cells per 10 high power fields (1-8 mm length epithelium). Ciliated cells are sparse proximally and increase in number progressively toward the periphery, while basal and migratory cells are most frequent proximally. At all levels of the airway, between 40% and 50% of cells are non-ciliated. In the upper trachea the most frequent cell type was the 'intermediate', elsewhere the 'epithelial serous' cell. Goblet cells were few at all levels, amounting to less than 1% of the total counted. The Clara cell was not restricted to the terminal bronchioles but was found as far proximally as the hilum.

Two-toed sloths are larger than three-toed forms and potentially have the capacity for greater strength and power associated with their high frequency of suspensory behaviors. However, fiber architecture and whole muscle functional capacities remain completely unknown for either species of Choloepus. Part two of this study provides novel quantifications of muscle architectural properties in the forelimb of Hoffmann's two-toed sloth (C. hoffmanni). A suite of geometric measurements, including muscle mass, belly length, fascicle length, and pennation angle, were used to calculate physiological cross-sectional area (PCSA) and estimate isometric force, joint torque, and instantaneous power. In general, the musculature becomes progressively more pennate from the extrinsic to the distal intrinsic regions of the forelimb, and all flexors are larger than their counterpart extensors. Except for a few pairs of small joint stabilizer muscles, the majority of bellies in each region of the forelimb have greater ability for shortening but limited ability for sized-scaled force production. Nonetheless, several large, strong shoulder (e.g., m. latissimus dorsi) and elbow (e.g., m. brachioradialis) flexors are capable of applying large joint torques over an extended range of contractile excursion by having elongated moment arms. Modification to limb muscle gearing is further exemplified by pairs of synergistic muscles with opposing fast joint rotational velocity versus mechanical advantage arrangements in each functional group. Lastly, the digital flexors have variable architectural properties, but their collectively large PCSA and estimated maximum force production capability (~2.2× bodyweight force) indicates exceptional grip strength. The muscle functional properties determined herein match well with the observed myological traits in Choloepus and provide further evidence of their abilities for frequent and prolonged suspension that are divergent from three-toed sloths.

Dendritic spines are postsynaptic specializations that mainly contact excitatory inputs and modulate a wide range of processes involving synaptic transmission and plasticity. Based on morphological features, they were classified into stubby, wide, thin, mushroom, ramified, and double spines. However, spines display other than these "classical" shapes, which are morphologically more convoluted and were initially called "atypical" spines. They have been much less studied and, then, worthy of investigation. Here, atypical (or, rather, multimorphic) spines, as well as complex dendritic protrusions, were examined using the Golgi method and after 2D and 3D image reconstructions in dendrites, cell bodies, and axon hillocks of several neuron types from both rats and humans. A variety of morphological features of complex dendritic protrusions and multimorphic spines were characterized in basket cells, Purkinje cells, brush neurons and granule cells of the cerebellum, in multipolar neurons of the inferior olivary nucleus, in multipolar neurons of the posterodorsal medial amygdaloid nucleus, in short-shaft pyramidal neurons of the hippocampus, in layers V-VI pyramidal and polymorphic neurons of the prefrontal cortex, and layers II-VI neurons of the anterior cingulate, precuneus, temporal, and occipital cortex. We provide evidence for the usual occurrence of these multimorphic spines, characterized by their heterogeneity in shape and size, and discuss the likely functional implications for synaptic processing, intraspine microdomains, compartmentalization features, and plasticity. Given their presence in rodents and humans, we also discuss the possible implications of multimorphic spines for more complex synaptic transmission across evolved neural circuits, laying the groundwork for future research.

The development of the human midface is still partly unknown. Despite much research, some aspects of dimorphism and growth trajectories during childhood remain unclear, due to the complexity and interdependence of structures such as the sphenoid bone or the maxilla, although various analytical methods, such as anthropometric measurements, geometric morphometry, and surface registration techniques, have been put in place and continue to be optimized for a better understanding of this complex development. We therefore set out to develop a surface registration method without segmentation, through a MultiSlice Computed Tomography (MSCT) study of midface development in immature children aged 0 to 15 years. This study tested the feasibility of this method by creating mean shapes by sex and age, and producing colorimetric maps of intersex deformation within age and intrasex deformation between adjacent ages, in order to visualize the effects of growth and dimorphism on midface shape, independently of size. To ensure clarity of analysis, only results from individuals aged 3, 9, 11, and 15 years were reported, focusing on the maxillary arch, maxillary sinuses, and palate. The results reveal sex and age differences, observed through voxel contractions and dilations in the images. These deformations appear to be linked to dental eruptions and associated bone remodeling, which also lead to inferior displacement of the maxillary sinuses during growth. Furthermore, it was noted that these processes manifest themselves earlier in female individuals, while male individuals show more robust teeth and structures by the end of puberty. Finally, although the results obtained with this method are promising, further efforts are needed due to the many challenges encountered during the process, and will provide a better understanding of maxillary growth, enabling better prevention of pathologies linked to this zone, better diagnosis, and development of early treatments for these pathologies.

Research on brain evolution centres mainly on internal mouldings of the skull, known as endocasts; however, the relationship between the size and asymmetry of the brain and endocasts has been poorly investigated in humans. Therefore, the main objective of this study was to investigate whether endocasts can be reliable indicators of brain size and asymmetry. Magnetic Resonance Imaging (MRI) of 75 participants was used to calculate the volume and surface area of the brain, the endocast, and their respective hemispheres. Two asymmetry indices (i.e. directional and absolute asymmetry) were used to assess the differences in volume and surface area between the sides of the brain and endocast. The Pearson correlation coefficient was calculated to assess the relationships between the parameters, and a Monte Carlo simulation for linear regression was performed to generate prediction equations for brain volume. The relationships between the level and direction of asymmetry indices were investigated using the Pearson correlation and McNemar's test, respectively. All correlations were statistically significant; however, correlation coefficients between volumes were stronger (0.894-0.931) than between volumes and surface areas (0.783-0.834). Brain volume can be predicted with high accuracy (ranging between 0.80 and 0.87) using the endocast total volume or the volume of one of the sides. The associations between the levels of asymmetry indices of the brain and endocast were non-significant; however, the McNemar's test indicated that endocasts show the same left- or right-biased asymmetry as the brain. This was the first study conducted on a large sample of brain and endocast data from the same individuals. The results demonstrated that brain volume can be accurately reconstructed using the volume of the endocast or one of its sides. This finding is especially important in the context of reconstructing fossil skulls, which are usually fragmented. Conversely, the asymmetry levels of endocast parameters are not reliable indicators of the actual level of brain volume asymmetry. Future research on fossils should focus on endocast asymmetry direction (left- or right-biased) as this closely corresponds with brain lateralisation.

As part of the jaw joint, the quadrate is a key skeletal element of the feeding system in nonmammalian vertebrates, which plays a critical role in resisting joint reaction forces (JRF). Some authors have suggested that the quadrate orientation reflects overall muscle anatomy and, by implication, JRF. Here, we quantitatively test the longstanding hypothesis that quadrate orientation is correlated with JRF orientation using the suchian lineage leading to extant crocodylia. The evolution of the characteristic crocodylian skull is a major transformation in vertebrate evolution in which the quadrate played a crucial role. We use detailed, three-dimensional biomechanical modeling to estimate JRF in a sample of eleven fossil and extant suchians and compare these to the orientation of quadrates. We use the cross-product of orientation vectors to quantify similarity in orientation and show that the angle of the quadrate in the sagittal plane is tightly coupled with JRF in the same. These results demonstrate a coordinated evolution between JRF and quadrate anatomy during suchian evolution and provide a framework with which to analyze evolutionary changes in joint anatomy and biomechanics.