Journal of Anatomy最新文献

Opossums (marsupials of the Didelphidae family) retain a generalized masticatory apparatus and tribosphenic molars, often used as models to understand the evolution of mastication in early therian mammals. Like all marsupials, their growth goes through a stage when pups complete their development while permanently attached to the mother's teats before weaning and starting feeding on their own. Yet, while the masticatory muscles of adults are known, as is the ontogeny of the cranium and mandible, the ontogenetic changes in the masticatory muscles remain unknown. Here we describe for the first time the changes in the masticatory muscles observed in lactating pups, and weaned juveniles, subadults, and adults in the White-eared opossum, Didelphis albiventris, through dissection of 25 specimens and quantification of relative muscle masses, lines of actions and mechanical advantages whenever possible. We also assessed the scaling patterns of muscle masses and mechanical advantages through ontogeny. The main changes, as expected, were found between suckling and weaned specimens, although some changes still occurred from juveniles to adults. The adult adductor musculature is similar to the other Didelphis species already known, with a dominant m. temporalis that originates on the lateral wall of the skull, up to the sagittal and nuchal crests, and fills the zygomatic arch when inserting into the lateral and medial surfaces of the coronoid process, respectively through the pars superficialis and pars profunda. The m. masseter is also subdivided in superficial and deep bundles which originate posteriorly in the maxilla and zygomatic arch, and insert into the angular process and masseteric fossa in the mandible. The m. pterygoideus medialis originates from the palatine, the pterygoid bone and the alisphenoid, and it inserts on the angular process medially. Suckling pups showed muscles with more restricted attachments, reduced muscle lines of action, and less diversity in the fiber orientation. The absence of the postorbital constriction also resulted in a distinct morphology of the m. temporalis pars profunda, through two bundles, one anterior and one posterior, which insert more inferiorly into the mandible. These major changes can be related to the onset of mastication and to size-related changes in growing weaned age classes. In general, all adductor muscles grew with positive allometry, and increased their fixation areas through, in part, the development of specific regions of the cranium and mandible. Their lines of action also increase and diversify along ontogeny. These changes can be related to the functional requirements for fixation during lactation, which shift to adduction and mastication movements after weaning.

The Upper Jurassic Morrison Formation sauropods Diplodocus (formerly "Seismosaurus") hallorum and Supersaurus vivianae are quantifiably the largest dinosaurian taxa from the formation, as well as being among the largest dinosaurs in the world. Their extreme body size (in particular body length, c. 50+ m) has fascinated the paleontological community since their discoveries and has sparked an ongoing discussion on the trends and limits of Morrison Formation sauropod body size. Although not an undeviating proxy, often the largest and skeletally most mature specimens are among the rarest (as exemplified in Triceratops). While their body size has no phylogenetic bearing, the extreme size and potential eco and biological significance of these two sauropod taxa are frequently discussed. Whether these rare and titanically proportioned sauropod specimens are large-bodied, senescent or both is an often-repeating rhetoric. To definitively make maturational inferences about these taxa, we osteohistologically sampled the holotype of D. hallorum (NMMNH P-25079) and the second known specimen of S. vivianae (WDC DMJ-021). Our age-determinant and maturational assessments indicate that both specimens were skeletally mature at their respective age of death. Retrocalculation methods for D. hallorum NMMNH P-25079 produce a maximum age-at-death estimation of 60 years, whereas S. vivianae WDC DMJ-021 lived well past skeletal maturity-so much so that reliable retrocalculated ages cannot be accurately determined at this time. Additionally, the rarity of such large sauropods within the Morrison Formation might be more parsimoniously explained as relating to their maturity as opposed to representing aberrant taxa on the Morrison landscape.

The nuclei are the main output structures of the cerebellum. Each and every cerebellar cortical computation reaches several areas of the brain by means of cerebellar nuclei processing and integration. Nevertheless, our knowledge of these structures is still limited compared to the cerebellar cortex. Here, we present a mouse genetic inducible fate-mapping study characterizing rhombic lip-derived glutamatergic neurons of the nuclei, the most conspicuous family of long-range cerebellar efferent neurons. Glutamatergic neurons mainly occupy dorsal and lateral territories of the lateral and interposed nuclei, as well as the entire medial nucleus. In mice, they are born starting from about embryonic day 9.5, with a peak between 10.5 and 12.5, and invade the nuclei with a lateral-to-medial progression. While some markers label a heterogeneous population of neurons sharing a common location (BRN2), others appear to be lineage specific (TBR1, LMX1a, and MEIS2). A comparative analysis of TBR1 and LMX1a distributions reveals an incomplete overlap in their expression domains, in keeping with the existence of separate efferent subpopulations. Finally, some tagged glutamatergic progenitors are not labeled by any of the markers used in this study, disclosing further complexity. Taken together, our results obtained in late embryonic nuclei shed light on the heterogeneity of the excitatory neuron pool, underlying the diversity in connectivity and functions of this largely unexplored cerebellar territory. Our findings contribute to laying the groundwork for a comprehensive functional analysis of nuclear neuron subpopulations.

Leavey, A., Ruta, M., Richards, C.T. and Porro, L.B., 2023. Locomotor, ecological and phylogenetic drivers of skeletal proportions in frogs. Journal of Anatomy, 243(3), 404–420. https://doi.org/10.1111/joa.13886

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At the angle of the mouth, spoke-like muscle bundles converge at the “modiolus,” which is believed to appear in utero. The aim of this study was to investigate the growth of the modiolus histologically. We studied frontal histological sections of the face from 12 midterm and six near-term fetuses. At midterm, a convergence of the levator anguli oris (LAOM) and depressor anguli oris (DAOM) was frequently present, and another convergence of the LAOM with the platysma (PM) or orbicularis oris (OOM) was also often evident. At near-term, muscle fiber merging or interdigitation was classified into nine combinations, five of which were frequently seen: LAOM-PM, LAOM-DAOM, zygomaticus major (ZMM)-orbicularis oris (OOM), buccinator (BM)-LAOM, and BM-PM. These combinations existed at slightly different depths and/or sites, thus allowing the angle of the mouth to receive multiple muscles. Notably, tissues interposed between the muscle fibers were limited to a thin epimysium at each crossing or interdigitation. Therefore, the LAOM, DAOM, OOM, BM, and PM appear to form a basic configuration at birth, but the development and growth were much delayed than the classical description. The modiolus is not a specific fibromuscular structure but simply represents a cluster of muscle convergence sites. Even at meeting between an elevator and depressor, a specific fibrous structure seems unlikely to connect the epimysium for the muscle convergence. Instead, the central nervous system appears to regulate the activity of related muscles to minimize tension or friction stress at the meeting site.

In reading the published letter to the editor by Drs Venkatesh and Morris, they raise a number of points concerning educating students about developmental embryology, along with clinical (and presumably legal) considerations concerning individuals with DSDs or gender. Its publication is timely, given the recent debates in the wider medical community, and in public, following the publication of the Cass report, and the “WPATH files” (by Michael Shellenberger). While typical developmental embryology, and examples of variations, should rightly be included within the undergraduate curriculum (and has traditionally been taught pre-clinically by anatomists), establishing the extent to which diagnosis and management of DSDs and gender dysphoria should be included within modern undergraduate curricula is surely more appropriate for our specialist Clinical Colleagues to determine.

Morphological markers for brain plasticity are still lacking and their findings are challenged by the extreme variability of cortical brain surface. Trying to overcome the "correspondence problem," we applied a landmark-free method (the generalized procrustes surface analysis (GPSA)) for investigating the shape variation of cortical surface in a group of 40 healthy volunteers (i.e., the practice group) subjected to daily motor training known as Quadrato motor training (QMT). QMT is a sensorimotor walking meditation that aims at balancing body, cognition, and emotion. More specifically, QMT requires coordination and attention and consists of moving in one of three possible directions on corners of a 50 × 50 cm². Brain magnetic resonance images (MRIs) of practice group (acquired at baseline, as well as after 6 and 12 weeks of QMT), were 3D reconstructed and here compared with brain MRIs of six more volunteers never practicing the QMT (naïve group). Cortical regions mostly affected by morphological variations were visualized on a 3D average color-scaled brain surface indicating from higher (red) to lower (blue) levels of variation. Cortical regions interested in most of the shape variations were as follows: (1) the supplementary motor cortex; (2) the inferior frontal gyrus (pars opercolaris) and the anterior insula; (3) the visual cortex; (4) the inferior parietal lobule (supramarginal gyrus and angular gyrus). Our results show that surface morphometric analysis (i.e., GPSA) can be applied to assess brain neuroplasticity processes, such as those stimulated by QMT.

Early diagnosis of post-traumatic osteoarthritis (PTOA) is critical for designing better treatments before the degradation becomes irreversible. We utilized multimodal high-resolution imaging to investigate early-stage deterioration in articular cartilage and the subchondral bone plate from a sub-critical impact to the knee joint, which initiates PTOA. The knee joints of 12 adult rabbits were mechanically impacted once on the femoral articular surface to initiate deterioration. At 2- and 14-week post-impact surgery, cartilage-bone blocks were harvested from the impact region in the animals (N = 6 each). These blocks were assessed for deterioration using polarized light microscopy (PLM), microcomputed tomography (μCT), and biochemical analysis. Statistically significant changes were noted in the impact tissues across the calcified zone (CZ) at 14 weeks post-impact: the optical retardation values in the CZ of impact cartilage had a drop of 29.0% at 14 weeks, while the calcium concentration in the CZ of impact cartilage also had a significant drop at 14 weeks. A significant reduction of 6.3% in bone mineral density (BMD) was noted in the subchondral bone plate of the impact samples at 14 weeks. At 2 weeks post-impact, only minor, non-significant changes were measured. Furthermore, the impact knees after 14 weeks had greater structural changes compared with the 2-week impact knees, indicating progressive degradation over time. The findings of this study facilitated a connection between mineralization alterations and the early deterioration of knee cartilage after a mechanical injury. In a broader context, these findings can be beneficial in improving clinical strategies to manage joint injuries.

Although extinct sloths exhibited a wide range of dietary habits, modes of locomotion, and occupied various niches across the Americas, modern sloths are considered quite similar in their habits. The dietary habits of living sloths can be directly observed in the wild, and understanding the mechanical behavior of their jaws during chewing through finite element analysis (FEA) provides a valuable validation tool for comparative analysis with their extinct counterparts. In this study, we used FEA to simulate the mechanical behavior of sloth mandibles under lateral mastication loads, using it as a proxy for oral processing. Our research focused on the six extant sloth species to better understand their diets and validate the use of FEA for studying their extinct relatives. We found that all living sloths have the predominancy of low-stress areas in their mandibles but with significant differences. Choloepus didactylus had larger high-stress areas, which could be linked to a reduced need for processing tougher foods as an opportunistic generalist. Bradypus variegatus and Choloepus hoffmanni are shown to be similar, displaying large low-stress areas, indicating greater oral processing capacity in a seasonal and more competitive environment. Bradypus torquatus, Bradypus pygmaeus, and Bradypus tridactylus exhibited intermediary processing patterns, which can be linked to a stable food supply in more stable environments and a reduced requirement for extensive oral processing capacity. This study sheds light on extant sloths' dietary adaptations and has implications for understanding the ecological roles and evolutionary history of their extinct counterparts.

Current studies on facial growth and development have been largely based on European populations. Less studied are African populations, who because of their distinct genetic makeup and environmental conditions, provide deeper insights into patterns of facial development. Patterns of facial shape development in African populations remain largely uncharacterised. Our study aimed to establish facial growth and development trajectories based on a cohort of 2874 Bantu Africans from Tanzania aged 6–18 years, with particular focus on identifying morphogenetic processes that lead to observed developmental shape changes. Procrustes ANCOVA suggested sexually dimorphic patterns of facial shape development (p = 0.0036). The forehead was relatively contracted during development in both sexes. The glabella region was more anteriorly displaced in females due to expansion in the region laterosuperior to the eyes. Nasal protrusion increased with development, which was found to arise from local expansion in the nasal alae and columella. Local expansion in the upper and lower labial regions resulted in forward displaced lips in both sexes, with the effect more pronounced in males. The mentum was displaced more anteriorly in females due to comparatively more expanded mental regions with development. The lateral facial region corresponding to the underlying body of the mandible were developmentally expanded but were posteriorly positioned due to protrusive growth of surrounding structures. Generalised additive modelling of Procrustes variance suggested that facial variation decreased non-linearly with age (p < 0.05). Relative principal component analysis suggested that variations in facial outline shape were developmentally constrained, whereas nasolabial and mental regions, where developmental changes were significant, became morphologically diversified with development. In contrast to simple descriptive illustration of facial shape development, we gained transformative insights into patterns of facial shape development by analysing morphogenetic processes and variational properties. Our analytical framework is broadly applicable to morphometric studies on ontogenetic shape changes.