Journal of Anatomy最新文献

The neosuchian crocodyliform clade Pholidosauridae had a near-cosmopolitan distribution, spanning the Late Jurassic to the early Paleocene. Representatives of the group inhabited aquatic environments, ranging from freshwater to potentially fully marine forms. The phylogenetic placement of Pholidosauridae within Neosuchia remains debated: whereas most analyses place it as closely related to Dyrosauridae, some studies argue for a closer relationship with Goniopholididae. One skeletal region that could shed light on both the phylogenetic position of Pholidosauridae, as well as how it achieved its broad distribution, is the internal cranial anatomy, which has been shown to document morphological features with both an ecological and phylogenetic signal in other crocodyliforms. However, a natural endocast is currently the only available information on the internal cranial anatomy of a pholidosaurid. Here, we present new insights into the internal cranial anatomy of Pholidosaurus purbeckensis, based on CT-scan data of material from the lowermost Cretaceous Purbeck Limestone Group, southern UK. Overall, the endocranial anatomy of P. purbeckensis is more similar to that of goniopholidids than dyrosaurids, especially the morphology of the olfactory tract and the cerebrum, which might represent a phylogenetic rather than ecological signal. However, this might merely reflect retention of the 'standard' crocodyliform skull and endocranial shape in pholidosaurids and goniopholids, rather than necessarily a close relationship, with the cranial anatomy of dyrosaurids instead representing an apomorphic departure from this morphology. We identify paired dorsolateral expansions in the olfactory region of the skull of P. purbeckensis, which have been interpreted as osteological correlates of nasal salt glands in some marine thalattosuchians, dyrosaurids, and extinct gavialoid crocodylians. If this interpretation is correct, it would suggest a higher tolerance for saltwater than previously hypothesised in Pholidosaurus, which would provide support for oceanic capabilities early in the evolution of Pholidosauridae that potentially enabled the group's near-cosmopolitan distribution. Finally, we demonstrate external cranial anatomical variation amongst specimens attributed to P. purbeckensis, particularly in contemporaneous French remains provisionally referred to this species. However, this might best be regarded as individual variation: we therefore tentatively support the attribution of this material to P. purbeckensis pending the much-needed revision of the type species of Pholidosaurus, P. schaumburgensis, from the earliest Cretaceous of Germany.

The defining features of the upper limb congenital anomaly, radial dysplasia (RD), involve both skeletal and soft tissue malformation, including muscle, vascular, and neural structures, with varying degrees of severity. Herein, we summarise the range of soft tissue anatomy malformations that have been described in RD, with the objective of better understanding their aetiology and clinical significance. Changes to muscle anatomy can include hypoplasia and fusion; vascular defects often involve persistent median arteries and absent radial arteries. There are also consistent differences in neural projections that have consequences on surgical approaches. Understanding these changes from normal anatomy, their origins and variations is important for improving diagnosis, management, and surgical outcomes in RD.

EMILIN family extracellular glycoproteins in the basilar membrane (BM) have so far only been identified in the mouse. It may influence the stiffness and extracellular filamentous architecture essential for cochlear frequency tuning (Russell et al., 2020, Science Advances, 6, eaba2634). In our study, we explored whether elastic components, such as EMILIN-2 (elastin microfiber interface-located protein 2) and elastin, are also present in the human BM. In addition, we analyzed the fine morphology of the BM and tympanic covering layer (TCL) at different frequency locations using light, transmission electron, and scanning electron microscopy (LM, TEM, and SEM) in well-preserved human cochlear specimens. Tonotopic estimations were made from model extrapolations using synchrotron radiation phase-contrast imaging (SR-PCI) and 3D reconstruction of matched cochleae with delineated octave bands constructed using Greenwood's formula (Greenwood, 1961, Journal of the Acoustical Society of America, 33, 1344). Our immunohistochemistry and gene RNA sequencing (RNA-seq) data support that EMILIN-2 and elastin are expressed in the human BM. Expression pattern of both proteins that influence BM architecture vary along the frequency range. TEM analysis suggests that TCL cells are actively involved in the deposition of the amorphous substance and fibrillary network, conceivably serving to assemble extracellular and elastic constituents along the BM. Thus, our findings suggest that TCL cells may play an important functional role in human cochlear tuning, particularly at low frequencies potentially linked to our remarkable speech and music perception.

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.

Cover image: Face and leading edges of the pinnae of the Tadarida brasiliensis specimen used in the study by R. Carter, ‘A computational model of pinna tubercle aerodynamics in the fast-flying bat, Tadarida brasiliensis’, this issue.

Cartilage thickness in mammalian joints increases with higher body masses. Contradicting previous studies found this increase to be positive allometric or negative allometric. Since approaches like computational modelling of animal locomotion, muscle moment arms, and joint dynamics rely on estimates of joint spacing (JS), it is important to accurately estimate an animal's cartilage thickness based on body mass. Here, we measured ex vivo internal joint distances (IJDs) or bone-to-bone distances on CT scans of fresh cadaveric forelimbs in a sample of small- to medium-sized mammals. IJDs were measured in the humero-ulnar and humero-radial joint. We find IJDs to scale isometrically in both joints across the entire sample, with positive allometric tendencies only within a subsample of cursorial species and only in the humero-ulnar articulation. The previously reported positive allometry can be linked to a cursorial sampling bias, and negative allometry results from a size constraint, acting on larger mammals than sampled here. Additionally, the IJDs were not affected by limb poses (i.e., flexed to extended, supinated, pronated). In rats and guinea pigs of varying sizes, we observed intraspecific isometric scaling with slight positive trends. This suggests that theoretically greater absolute forces-resulting from increased body mass with similar posture-only marginally contribute to relatively thicker cartilage in small- to medium-sized mammals. Further, we conducted a "range of motion" (ROM) analysis in the humero-ulnar joint of rats, guinea pigs, and maras, thus species of increasing body mass and level of cursoriality. ROM was assessed with varying estimated JS. Differences in the results are most biologically reasonable when allowing all six degrees of freedom (DOF, three rotational and three translational). Mobility decreases with increasing body mass and level of cursoriality, facilitated by increased restriction of movement to a single axis of flexion and extension. Such a trend persisted regardless of whether JS thresholds were estimated using intraspecific or interspecific regression models. The results suggest that variations in elbow mobility are less influenced by applied JS than by the morphological characteristics of the bones forming the joint. This observation has implications for future comparative studies of mammalian elbow function. Still, more research is needed to separate body mass, degree of cursoriality, or locomotor type as factors for elbow mobility.

We propose for the first time a direct comparison between brain and endocast characteristics-the number, position, length and proportion of sulci as revealed by the evidence on the brain and their corresponding marks on the endocast that is the internal surface of the skull-in the same living individuals. Using a tailored MRI imaging methodology developed to overcome the limitations inherent to medical imaging on healthy subjects, we compare 3D models of the brain and of the endocast obtained from the same cohort of 75 volunteers. These data were quantified in terms of observation frequency, proportion of dimension for the same structures on the endocast compared to the brain and variation among the analysed sample. We show that identifiable marks on the endocast are often short, discontinuous, and primarily located in the lower regions (particularly in the inferior frontal and temporal lobes areas). This observation contradicts previous practices of drawing long, straight marks on fossil endocasts. An unexpected result of the study is the discovery of endocranial marks unrelated to cerebral sulci, called MNAS (for endocranial Marks Not Associated with Sulci). These marks represent approximately 12% of the depressions observed and pose a challenge for the interpretation of fossil endocasts. Finally, we propose with this work a new standardised approach to studying fossil endocasts, which combines precise guidelines for sulci variation description as well as for inter-individual comparisons, and cross-validation by several researchers. The development of a new approach based on a large quantity of anatomical information presented in the present study, offers new perspectives for reconstructing the anatomy of fossil hominin's brain in a more objective framework, and will have a lasting impact for the study of the evolution of the hominin brain, particularly functional lateralisation and cognitive abilities.

Palaeoanthropology is highly dependent on anatomical knowledge. Anatomical descriptions and comparisons have long formed the basis of the discipline, allowing researchers to draw inferences about our ancestors' behaviour, biology, and locomotion, as well as to establish phylogenetic relationships between extinct hominins and define taxa within the fossil record. The integration of virtual anatomy methods, relying on high-resolution imaging, 3D modelling, and computational simulations, has revolutionised the field, enabling palaeoanthropologists to quantify anatomical variation, simulate biological processes, and reconstruct morphology in fossil material with unprecedented precision. In a field limited not only by the sole preservation of hard mineralised tissues such as bone and teeth, but also by their fragmentary condition and frequent geological or taphonomic distortion, the introduction of methods that allow analytical procedures to be shared, repeated, and performed non-destructively has greatly enhanced anatomical studies of extinct hominins. Moreover, despite the lack of direct evidence for soft tissues, the adaptive properties of bone, shaped by the muscles, tendons, and organs surrounding it and the forces they exert, now allow palaeoanthropologists to reconstruct muscle attachment sites, brain morphology, and other soft tissue-related structures. Researchers can also simulate bone responses to activities such as bipedal locomotion or tool use through static and dynamic modelling that enables them to virtually construct 'what-if' scenarios, effectively bringing to life some of the most iconic specimens in human evolution. Despite these advances, the field still has a long way to go. The recent introduction of AI algorithms to automate specific preprocessing phases (e.g., segmentation), alongside the ongoing need for methodological integration and broader access to technological resources, highlights the importance of developing a more open, replicable, and globally accessible toolkit for palaeoanthropologists worldwide.

Little is known on the keratinisation and cornification in the alligator tongue. This process has been studied during late and pre-hatching embryonic stages, using histochemical, immunolabelling and electron microscopy. The study revealed that PAS-positive, Alcian blue and Blue Nile Sulphate reactive glycoprotein/glycolipids are produced and accumulated in the corneous layer of the lingual epithelium before hatching. Also, Intermediate Filament Keratins (IFKs) but not Corneous Beta Proteins (CBPs) are synthesised in the tongue epithelium. Alligator IFKs have variable composition and cysteine content, 0.1%-1.1%, and few contain 2.5%-4.9% cysteine, and participate in the formation of a hard-corneous layer. These keratins also contain numerous hydrophobic amino acids, in particular leucine and valine, suggesting that they are partially hydrophobic. The predicted cross-reactivity with the IFK-antibodies here employed suggests that these antibodies can recognise some alligator IFKs. Light and transmission electron microscopy show that the stratified corneous layer is formed by narrow alpha-corneocytes storing peripheral corneous material and a central electron-pale and likely glycolipid core. Numerous membrane coating granules 0.1-0.2 μm in diameter and reactive to silver-methenamine reaction for glycoproteins are accumulated and merge with keratin bundles along the plasma membrane or are extruded among pre-corneous keratinocytes. Corneocytes of 0.1-0.2 μm in thickness pile up on embryonic tongue before hatching, forming the stratum corneum, but they do not accumulate detectable CBPs, the prevalent proteins instead present in alligator scales and claws. Whether CBPs are later produced in juveniles and adult alligator tongue to mechanically strengthen the lingual epithelium is unknown but it is hypothesised that the presence of cysteine-rich IFKs may contribute to the hardness of the tongue corneous layer.

Conventional embryological models propose that the urorectal septum (URS) fuses with the cloacal membrane (CM) to form separate exits for the hindgut and urogenital sinus (UGS). However, previous studies have been re-evaluating this assumption, and the precise morphogenetic mechanisms determining the position of the anal opening remain unclear. To elucidate the spatial and temporal dynamics of cloacal development, we analysed mouse embryos from embryonic day (E)11.5 to E13.5 using serial midsagittal histological sections combined with three-dimensional reconstruction. We focused on the positional relationship between the URS and CM, as well as the internal remodelling events of the cloaca that lead to anal opening formation. Throughout development, the URS enlarged and shifted distally, but consistently remained dorsodistal to the CM without direct fusion. At E13.0, we identified an expanded space at the caudal end of the hindgut, distinct from the hindgut lumen. By E13.25, this space connected to the UGS via a duct-like structure, contributing to the separation of the UGS and hindgut. By E13.5, the CM ruptured and the anal opening emerged precisely at the junction between the hindgut lumen and the expanded space. Our findings demonstrate that the position of the anal opening is predetermined by cloacal internal space remodelling rather than fusion of the URS and CM. This study offers novel insights into normal anorectal development and the aetiology of congenital anorectal malformations.