Journal of Anatomy最新文献

Gracilisuchus stipanicorum was a pseudosuchian archosaur from the Late Triassic period in Argentina. Because it was small-bodied with relatively long, slender limbs, traits that are potentially ancestral for archosaurs, such as its locomotor functions, are important to estimate. It has been illustrated as a quadruped with plantigrade autopodia, and probably with an 'erect' or 'semi-erect' stance, because it is a suchian archosaur, but there has been no deep analysis of these reconstructions. Here, we detail our reconstruction of a three-dimensional digital skeleton of Gracilisuchus from scans of the bones of four main specimens, including the holotype. In this procedure, we found hitherto unrecognised elements of the manus (metacarpals) and incorporated them in our model of the whole organism. We added estimated hindlimb musculature and body segment mass properties to form a musculoskeletal model. This model allowed us to address three key questions: Was it quadrupedal or bipedal; plantigrade or digitigrade; and more sprawling or more erect? Furthermore, we examine how its hindlimb muscle moment arms compare to those of three other small-bodied Triassic archosauriforms and an extant juvenile Nile crocodile in order to assess the diversity and potential evolutionary polarity of these traits. Our analyses of the model support the inferences that Gracilisuchus was quadrupedal (but facultative bipedalism cannot be ruled out) and plantigrade, and not strongly sprawling, but probably not strongly erect hindlimbs; although terming this posture 'semi-erect' would be an oversimplification. Gracilisuchus, as modelled here, seems to roughly be a reasonable approximation of the ancestral state of the archosaurian locomotor system. Our synthesis of numerous lines of evidence, from qualitative functional morphology to whole-body centre of mass and muscle moment arms, forms a new reconstruction of Gracilisuchus that future analyses can build on, both biomechanically and comparatively, in order to better understand archosauriform locomotor evolution.

Teeth are anchored in the jaw in a highly variable manner across vertebrates. In mammals and crocodiles, the teeth are cushioned inside bony sockets by periodontal ligaments, whereas most squamate reptiles have teeth firmly attached to the jawbone. Here, we analyzed the development of the attachment tissue in the veiled chameleon, a species with firm acrodont tooth attachment, to reveal the cellular processes establishing ankylosis and to determine the cell types contributing to the attachment. The tooth-bearing bones formed pedicles with edges fusing to the dentine via an attachment tissue produced by morphologically distinct cells exhibiting both osteoblastic and odontoblastic features. These cells were RUNX2-positive, suggesting their potential to differentiate into hard-tissue-producing cells. However, in contrast to the osteoblasts of the bony pedicles, tooth–bone interface (TBI) cells expressed elevated levels of Na⁺-/K⁺-ATPase and thus resembled odontoblasts. TBI cells were visible only temporarily, and after tooth–bone fusion they were removed by apoptosis and phagocytosis. Dynamic deposition of the hard matrix continued on both sides of the TBI and during the posthatching stages through the participation of osteoblasts. Overall, our findings demonstrate both odontoblast- and osteoblast-like characteristics of cells producing the attachment tissue at the TBI during development in chameleons, highlighting the existence of a transient intermediate cell population, which we call ankyloblasts.

5-Hydroxytryptamine (5-HT), widely recognized as serotonin, is a multifunctional substance present across various body tissues, performing as a neurotransmitter within the nervous framework. Serotonergic neurons are predominantly localized within the raphe nuclei of the brainstem, rendering neuronal 5-HT a definitive marker for these nuclei. Research has substantiated serotonin's role in the modulation of thermoregulation, appetite, reproductive drive, circadian patterns, slumber, motoric activity, and cognitive processing. While the anatomical structure of serotonergic systems has undergone extensive review in mammalian species, such as rodents, rabbits, felines, and non-human primates, it remains unexplored in South American bat species. This investigation sought to delineate the serotonergic architecture in the cerebrum of Artibeus planirostris through the application of serotonin immunohistochemistry. The study used six adult males Artibeus planirostris (family Phyllostomidae, class Mammalia). Following anesthesia and perfusion, their brains were sectioned. Coronal brain sections were acquired using a sliding microtome and processed with an immunohistochemical assay specific to 5-HT. Caudal linear (CLi), dorsal (DR), median (MnR), paramedian (PMnR), pontine (PnR), magnus (RMg), pallidus (RPa), and obscurus (ROb) raphe nuclei, as well as the B9 and rostral and caudal ventrolateral (rVL/cVL) groups, were marked. Contrary to the serotonergic structures commonly observed in bats, A. planirostris dorsal raphe showed a distinct nuclear subdivision, while the median raphe exhibited bilateral representation. The morphometric analysis in this study does not show significant differences in the size of the neuronal area among raphe nuclei. Fresh insights into the field of neuroanatomy are offered by these results, which emphasize potential variations in brain structure among echolocating species in South America as opposed to the more commonly researched models in bats, rodents, and non-human primates.

Globally, human population structure is quickly trending older, increasing the prevalence and systemic burden of age-related skeletal disorders such as osteoporosis. Osteoporosis is characterized by the loss of bone mass, including trabecular bone tissue, leading to skeletal fracture. Although clinically important, fundamental questions remain about normal trabecular bone variation and age-related bone loss. In this study, we use free-ranging rhesus macaques (Macaca mulatta) from the Cayo Santiago Field Station to explore variation in trabecular bone structure. We measured several aspects of trabecular bone structure (maximum and mean bone volume fraction, degree of anisotropy, and trabecular thickness) across the elbow (humerus, ulna, radius), hip (proximal femur), and knee (distal femur, tibia). Analyses of covariance models assessed factors influencing bone structure, including body mass, demography (age, sex, matriline), as well as indices of sociality and early life adversity. Point cloud models of prime and postprime age groups visualized age-related differences in bone structure. We observed significant variation in trabecular bone morphology (max and mean bone volume fraction, degree of anisotropy, and trabecular thickness) across both bones and joints. Sex influenced trabecular thickness, with thicker trabeculae in males. Max and mean bone volume fraction as well as trabecular thickness were positively associated with body mass. Age was associated with significantly lower values of mean bone volume fraction, specifically in the hind limb. We observed significant bone loss specifically in the femoral head and neck. There were no associations of trabecular bone structure with either sociality or early life adversity in this sample. This study provides a comprehensive view of trabecular bone variation by region, sex, mass, and age contextualized by social factors.

The sacroiliac joint allows limited but crucial movement for transmitting loads from the spine to the pelvis. Identifying anatomical structures that adapt to this motion may improve imaging-based diagnosis of sacroiliac joint dysfunction. The interosseous sacroiliac ligament (ISIL), a key stabilizer connecting the sacrum and ilium, has unclear adaptive responses to mechanical stress. This study aimed to investigate the ISIL's gross morphology, fiber orientation, and histological features. A total of 11 hemipelves from eight donors were examined, six for gross anatomy and five for histology. Fiber orientation was evaluated using micro-computed tomography. The distribution of fiber angles was compared between the superior and inferior ISIL regions, ranging from +90° (vertical) to -90°, using paired t-tests with statistical parametric mapping. The ISIL displayed a consistent fibrous architecture, with predominantly vertical fibers in the inferior region and a higher frequency of horizontal fibers in the superior region. Orientation analysis revealed more vertical fibers (70°-80°) inferiorly and more horizontal fibers (-50° to -30°) superiorly (p < 0.05). Histology confirmed these findings and revealed a synovial bursa-like structure between the ISIL and the posteroinferior sacrum. These findings suggest that the ISIL exhibits region-specific fiber alignment, with vertical fibers inferiorly and horizontal fibers superiorly, along with a synovial bursa-like structure adjacent to the sacrum. These patterns likely reflect mechanical adaptation to sacroiliac joint motion and may guide imaging-based assessment of sacroiliac joint dysfunction. Our suggestion requires validation based on the direct mechanical data through biomechanical and clinical research, and the limitation of quantitative analysis being 2D and having a small sample size need to be addressed in future studies incorporating in vivo 3D imaging.

The posterior layer of the thoracolumbar fascia, which includes the aponeuroses of several skeletal muscles among its components, has long been of interest in relation to low back pain. This layer has been described as consisting of two laminae, a superficial and deep. These laminae are known to fuse tightly at a lower thoracic level, forming a unified posterior layer. However, the precise anatomical continuity of these components, particularly in the lower lumbar and sacral regions, remains unclear. Therefore, we performed a comprehensive macroscopic analysis of the posterior layer, focusing on the composition and orientation of collagen bundles (CB) within the aponeurosis of its component muscles, while taking anatomical variations into account. We examined 17 sides from 11 cadavers, focusing on the lumbar to the upper sacral vertebral region. In all specimens, no distinct retinacular sheet could be separated from the aponeurotic complex of the posterior layer, even in the lower lumbar and sacral regions where previous studies illustrated a deep lamina. In the upper lumbar region, the aponeuroses of the latissimus dorsi (LD) and serratus inferior muscles contributed to the posterior layer, forming a continuous structure that could not be divided into distinct layers. Meanwhile, in the lower lumbar region, the posterior layer comprised the aponeuroses of the LD and internal oblique muscles, along with a bundle of fibers extending from the periosteum of the iliac crest. In the upper sacral region, the posterior layer comprised the aponeurosis of the LD, erector spinae, and gluteus maximus muscles, together with the bundle of fibers from the periosteum of the iliac crest. Despite some variations in the site of muscle attachment, the posterior layer consistently contained CB that are inferolaterally oriented from the lumbar to iliac crest spinous processes between the lumbar and upper sacral vertebrae, in a direction independent of the orientation of muscular aponeuroses. These consistent directional patterns may suggest a functional integration of muscular and fascial components, regardless of anatomical variation. Considering the structural features of the posterior layer, further studies are needed to clarify how dynamic changes in this layer during trunk movement may contribute to clinical conditions, including low back pain.

Textbooks locate the junction between the midgut and hindgut where the vascular beds of the superior (SMA) and inferior (IMA) mesenteric arteries meet. In a previous study, we observed that the formation of the midgut corresponded with a pronounced thinning of its dorsal mesentery. We re-investigated, therefore, the location of the distal boundary of the midgut, making use of 3D reconstructions of serial sections of 36 human embryos between 4 and 13 weeks of development. Using the boundaries of the thin mesentery of the midgut as a criterion, the midgut-hindgut junction corresponds in 10-week and older foetuses with the rectosigmoid junction. In addition, we established that the 3D orientation of the trunk of the IMA (between its aortic root and first branching node) also identifies the position of the midgut-hindgut junction in the gut. The growth rate of the early colon is exponential, whereas that of the rectum is linear. Initially, the foetal colon has ascending and descending limbs only, of which the descending limb grows fastest. The mesentery of the ascending colic limb adheres to the ventral surfaces of the duodenum, stomach and dorsal pancreas shortly after the hernial return into the abdomen during the 10th week, which rules out an effect of differential growth on the position of the junction. We, therefore, postulate that the rectum is the sole descendant of the embryonic hindgut. The rectum is unique in that its differentiation follows a caudocranial direction. Vascular connections between the perfusion areas of the SMA and IMA expand to form the first colic arterial arcade only at 10 weeks.

Down syndrome (DS) is caused by an extra copy of human chromosome 21 (HSA21) and is associated with significant craniofacial anomalies among other systemic traits. While animal models have been pivotal in advancing DS research, most of the mouse models replicate only a portion of the human genetic condition. The recently developed transchromosomic rodent models of DS, TcMAC21 mice, and TcHSA21rat carry nearly complete copies of HSA21q and all of HSA21, respectively. While both TcMAC21 and TcHSA21rat express DS-like craniofacial malformations, no comprehensive interspecies comparisons have been conducted between the two. Here, we quantitatively compare the craniofacial skeleton of TcMAC21, TcHSA21rat, and their respective unaffected littermates using high-resolution micro-computed tomography images, landmark-based geometric morphometrics, and advanced multivariate statistics to assess overall craniofacial shape and integration patterns between the neurocranial and facial components. Both models reflect the craniofacial morphology of DS, exhibiting increased neurocranial globularity (supero-inferiorly) and overall facial retraction (anteroposteriorly). However, the rat model expresses a more prominent brachycephalic phenotype compared with its murine counterpart. The integration between the cranial components was found to be evolutionarily conserved across species; however, the trisomic animals maintained their distinct DS-specific configuration compared with their euploid littermates. Our findings establish a methodological framework for cross-species comparisons in DS animal models and provide important insights into characteristic manifestations of trisomy 21 and evolutionarily conserved aspects of the mammalian craniofacial skeleton.

The auditory cortex is central to auditory perception, but its detailed structural organization in sheep (Ovis aries) has not been thoroughly investigated. In this study, we sought to address this gap by providing an in-depth anatomical description of the cytoarchitecture and myeloarchitecture of the sheep auditory cortex, using cresyl violet staining and the neurochemical markers myelin basic protein and parvalbumin. Cresyl violet tissue samples from four sheep were used to characterize cortical layers and cellular composition, revealing a six-layered organization with variations in cell density and distribution. Myelin basic protein staining highlighted myelinated regions, while parvalbumin staining identified the distribution of a subpopulation of GABAergic interneurons, indicating the potential location of the primary auditory cortex. Overall, the organization of the ovine auditory cortex aligns with findings in other mammals, suggesting a conserved neural architecture across species and supporting the idea of evolutionary conservation in auditory processing mechanisms.

The temporomandibular joint (TMJ) plays a key role in facilitating complex mammalian jaw movements required for daily life. It is formed between the condylar process of the mandible (or dentary bone) of the lower jaw, the glenoid (or mandibular) fossa of the squamosal/temporal bone in the upper jaw and an interposed fibrocartilage disc. Structural defects in any component of the TMJ can disrupt the entire joint, contributing to TMJ disorders. Embryonic defects in the condyle in mice have been shown to have an impact on the shape and development of the glenoid fossa, highlighting the importance of coordinated development of the two sides of the joint. Although recent research has focused on the condylar process, much less is known about the development and homeostasis of the glenoid fossa, and defects in the glenoid fossa are also evident in disease. Here, we have analysed the formation and molecular identity of the glenoid fossa using the mouse as a model. Our findings revealed distinct patterns of development of the fossa in the anterior, middle and posterior regions. Interestingly, the cartilage marker Sox9 was transiently expressed in the lateral branch of the glenoid fossa during early TMJ development, and the loss of Sox9 in Wnt1-cre;Sox9fl/fl mice resulted in the absence of this part of the fossa. Postnatal maturation of the murine glenoid fossa was marked by the initiation of a fibrocartilage layer, the formation of which coincided with the onset of independent feeding, suggesting a role for mechanical force in glenoid fossa fibrocartilage induction. In contrast to the condyle, the fossa fibrocartilage expressed low levels of FSP1, a marker of the stem/progenitor population of the condyle. Depletion of FSP1-positive cells by conditional diphtheria toxin activity in FSP1-Cre;DTA mice has previously been shown to cause a severe TMJ osteoarthritis phenotype and enlargement of the condylar head postnatally. Interestingly, here, we show that in reaction to changes in condylar shape, these mutants develop an increase in glenoid fossa angulation over time, associated with increased remodelling activity, particularly in the lateral branch of the fossa. These findings highlight that the fibrocartilage of the glenoid fossa and condyle are not equivalent and that changes in the condyle can have a knock-on secondary effect on the 3D structure of the fossa. This coordinated response would allow for alignment of the TMJ, maintaining function throughout life, even in the case of disease.