Journal of Anatomy最新文献

Front cover:

Cover image: see S.I. Quiñones and colleagues, 'Ontogeny and associated changes of the extinct sloth Simomylodon uccasamamensis (Xenarthra, Mylodontidae) from the Pliocene of the eastern Puna, Argentina', this issue.

Non-image forming (NIF) pathways, a specialized branch of retinal circuitry, play a crucial role supporting physiological and behavioral processes, including circadian rhythmicity. Among the NIF regions, the dorsal raphe nucleus (DRN), a midbrain serotonergic cluster of neurons, is also devoted to circadian functions. Despite indirectly send photic inputs to circadian centers and modulating their activities, little is known about the organization of retina-DRN circuits in primate species. To enhance our understanding of the intrinsic organization of NIF circuits and identify retinoraphe innervation in the common marmoset (Callithrix jacchus), a diurnal non-human primate model, we employed an anterograde tract-tracing method to labeling terminal/fibers with cholera toxin subunit B (CTb) and characterized the morphology of their projections. Our analysis revealed that sparse CTb⁺ retinal terminals are predominantly located in dorsal subdomain of the DRN, displaying two morphological types, such as simple en passant and R2-like terminals. This anatomical evidence suggests a phylogenetic stability of the retina-DRN projections in diurnal primate species, potentially serving as a significant source of photic modulation on the serotonergic profile in the DRN. However, functional significance in primate models remains uncertain. Our data provide a crucial anatomical foundation for understanding the functional aspect of this circuitry in primates, contributing to the comprehension of the phylogenetic pathways used by NIF functions, such as circadian rhythmicity.

Anecdotally, horses' gaits sound rhythmic. Are they really? In this study, we quantified the motor rhythmicity of horses across three different gaits (walk, trot, and canter). For the first time, we adopted quantitative tools from bioacoustics and music cognition to quantify locomotor rhythmicity. Specifically, we tested whether kinematics data contained rhythmic categories; these occur when adjacent temporal intervals are categorically, rather than randomly, distributed. We extracted the motion cycle duration (t_k) of two ipsilateral hooves from motion data of 13 ridden horses and calculated the ratios from two successive t_k values. We tested whether these ratios significantly fell within rhythmic categories and quantified how close they were to small-integer ratios, a rhythmic feature also present in animal vocalizations and human music. We found a strong isochronous pattern—a 1:1 rhythmic ratio, corresponding to the ticking of a clock—in the motion of single limbs for all gaits. We also analyzed the interlimb coordination of the two ipsilateral hooves' impacts to identify differences associated with the biomechanical patterns of the three gaits. We found an interlimb 1:1 rhythmic pattern for trot and 1:3 and 3:1 rhythmic categories for walk and canter. Our findings are a first step toward quantifying rhythmicity in horse locomotion and potentially the resulting rhythmic sounds, with possible implications as tools to detect gait irregularities. Overall, we show that rhythmic categories are a valuable tool for gait kinematic analysis and that they can be used to quantify temporal patterns in the motor domain.

Raoellidae are small artiodactyls from the Indian subcontinent closely related to stem cetaceans. They bring crucial information to understand the early phase of the land-to-water transition in Cetacea. If they are considered to be partly aquatic, the question of their dietary habits remains partly understood due to their "transitional" morphology. Raoellidae are largely documented by their cheek teeth and getting a better knowledge of their anterior dentition constitutes an additional proxy to discuss their feeding habits. In this work, we document the anterior dentition of Indohyus indirae from an unprecedented sample of in situ and isolated teeth from the locality of East Aiji-2 in the Kalakot area (Rajouri district, India). We propose identification criteria for upper and lower incisors and canines in raoellids. Based on CT scan data, virtual reconstruction of in situ dentition, and identification of the isolated incisors and canines, we reconstruct a composite anterior dentition of Indohyus supported by the correspondence of wear facets between upper and lower teeth. This constitutes the first attempt at reconstruction of the anterior dentition of a raoellid. We show that the upper incisors are caniniform and very similar morphologically, whereas the lower incisors are pointed but remain incisiform and quite different from one another. We also describe noticeable intraspecific variation, at the level of upper canines, suggesting a potential sexual dimorphism in this species. Upper and lower incisors are recurved, with the upper incisor row arranged on a widely opened arch. Taken altogether the anterior dentition forms a grasping device, allowing the animal to capture and secure food, a characteristic shared with stem cetaceans. This would mark the first step towards the carnivorous diet in these peculiar artiodactyls.

Argochampsa krebsi is a gavialoid crocodylian from the early Paleogene of North Africa. Based on its recovered phylogenetic relationship with South American species, it has been inferred to have been capable of transoceanic dispersal, but potential anatomical correlates for a marine lifestyle have yet to be identified. Based on CT scans of a mostly complete and well-preserved skull, we reconstruct the endocranial anatomy of Argochampsa and compare it to that of other gavialoids. We demonstrate that Argochampsa possesses concave depressions on the internal surface of the prefrontals and lacrimals, which have been inferred to represent osteological correlates for salt glands in unequivocally marine metriorhynchoid thalattosuchian crocodyliforms. The presence of these salt glands suggests that Argochampsa likely frequented pelagic environments and provides additional support for the capability of transoceanic dispersal within Gavialoidea. We also newly interpret osteological correlates for salt glands in the Miocene north African gavialoid Sutekhsuchus dowsoni, providing further support that saltwater tolerance was widespread and possibly ancestral in Gavialoidea, given that they have been previously reported in the Late Cretaceous-early Paleogene species Eosuchus lerichei and Portugalosuchus azenhae. In addition to these gavialoids, as well as metriorhynchids, we also identify these osteological salt gland correlates in the Paleocene northwest African dyrosaurid Rhabdognathus aslerensis, which represents another crocodyliform lineage thought to be capable of transoceanic dispersal. Given that dyrosaurids, gavialoids, and metriorhynchoids are distantly related lineages, the evolution of salt glands is likely a convergent ecological adaptation to the occupation of pelagic environments. Nevertheless, we demonstrate limited evaluation of the presence of these osteological correlates across Crocodyliformes, including within most extant species, such that it remains possible that they are much more widespread.

The Emperor Penguin Aptenodytes forsteri is the largest living species of penguin, found exclusively in Antarctica, and is unique in breeding during the winter. Consequently, fewer anatomical studies have been conducted on this species over time compared to others. This study aims to provide an updated and comprehensive description of the hindlimb musculature of Aptenodytes forsteri. The muscles of the thigh, shank and foot were compared along postnatal development. The results were compared with the muscles of swimming and diving birds and also with ground-dwelling taxa. By dissecting seven specimens, the origin and insertion were described in newborns, chicks and juveniles. Of the 37 muscles recognized, 19 correspond to the thigh, 14 to the shank, and four to the foot. Notably, the hindlimb muscles appear relatively developed compared to the overall body size in the newborns, showing considerable development in independent chicks, and reached full growth in the juvenile. The m. flexor hallucis brevis, m. extensor hallucis longus and m. lumbricalis were absent in all specimens, whereas the m. femorotibialis lateralis was found in only one specimen. Additionally, a branch of the m. flexor cruris medialis, originating in the abdominal area and merging with the pelvic portion before insertion, was observed in the newborn chicks. Aptenodytes forsteri showed similarities with Numida meleagris in the insertion of m. iliofibularis, and m. flexor cruris lateralis p. pelvica. These findings, along with other comparative results, constitute the first comprehensive descriptive study of the hindlimb musculature of Aptenodytes forsteri, including different ontogenetic stages.

The absence of a clear consensus on the definition and significance of fascia and the indiscriminate use of the term throughout the clinical and scientific literature has led to skepticism regarding its importance in the human body. To address this challenge, we propose that: (1) fasciae, and the fascial interstitia within them, constitute an anatomical system, defined as a layered body-wide multiscale network of connective tissue that allows tensional loading and shearing mobility along its interfaces; (2) the fascial system comprises four anatomical organs: the superficial fascia, musculoskeletal (deep) fascia, visceral fascia, and neural fascia; (3) these organs are further composed of anatomical structures, some of which are eponymous; (4) all these fascial organs and their structural components contain variable combinations and arrangements of the four classically defined tissues: epithelial, connective, muscle, and neural; (5) the overarching functions of the fascial system arise from the contrasting biomechanical properties of the two basic types of layers distributed throughout the system: one predominantly collagenous and relatively stiff, the other rich in hyaluronic acid and viscous, allowing for the free flow of fluid; (6) the topographical organization of these layers in different locations is related to local variations in function (e.g. unidirectional arrangements favor tensional loading, interwoven structures favor shear mobility) thereby accounting for both the system's universal functional aspects and the site-specific variations between them. A universal language related to fascia will break down linguistic barriers and facilitate cross-disciplinary cooperation, enabling scientists and practitioners from diverse backgrounds to contribute their expertise seamlessly.

Geometric morphometrics is used in the biological sciences to quantify morphological traits. However, the need for manual landmark placement hampers scalability, which is both time-consuming, labor-intensive, and open to human error. The selected landmarks embody a specific hypothesis regarding the critical geometry relevant to the biological question. Any adjustment to this hypothesis necessitates acquiring a new set of landmarks or revising them significantly, which can be impractical for large datasets. There is a pressing need for more efficient and flexible methods for landmark placement that can adapt to different hypotheses without requiring extensive human effort. This study investigates the precision and accuracy of landmarks derived from functional correspondences obtained through the functional map framework of geometry processing. We utilize a deep functional map network to learn shape descriptors, which enable us to achieve functional map-based and point-to-point correspondences between specimens in our dataset. Our methodology involves automating the landmarking process by interrogating these maps to identify corresponding landmarks, using manually placed landmarks from the entire dataset as a reference. We apply our method to a dataset of rodent mandibles and compare its performance to MALPACA's, a standard tool for automatic landmark placement. Our model demonstrates a speed improvement compared to MALPACA while maintaining a competitive level of accuracy. Although MALPACA typically shows the lowest RMSE, our models perform comparably well, particularly with smaller training datasets, indicating strong generalizability. Visual assessments confirm the precision of our automated landmark placements, with deviations consistently falling within an acceptable range for MALPACA estimates. Our results underscore the potential of unsupervised learning models in anatomical landmark placement, presenting a practical and efficient alternative to traditional methods. Our approach saves significant time and effort and provides the flexibility to adapt to different hypotheses about critical geometrical features without the need for manual re-acquisition of landmarks. This advancement can significantly enhance the scalability and applicability of geometric morphometrics, making it more feasible for large datasets and diverse biological studies.

Digital muscle reconstructions have gained attraction in recent years, serving as powerful tools in both educational and research contexts. These reconstructions can be derived from various 2D and 3D data sources, enabling detailed anatomical analyses. In this study, we evaluate the efficacy of surface scans in accurately reconstructing the volumes of the rotator cuff and teres major muscles across a diverse sample of hominoids. Additionally, we investigate whether muscle origin area, as a dissection-based observation, can reliably predict muscle volume. Our findings reveal that surface scans provide sufficient coverage to accurately reproduce the in situ volumes of the rotator cuff muscles. However, the volume of the teres major was estimated less reliably, suggesting that muscles with less distinct skeletal boundaries may present challenges for accurate reconstruction. Future studies will explore whether such muscles can be reconstructed with greater precision. Furthermore, we identify a significant correlation between the origin area and muscle volume for the supraspinatus, infraspinatus, and subscapularis muscles. These results suggest that muscle origin area can serve as a reliable predictor of muscle volume, offering a skeletal indicator for estimating muscle size in both extant and extinct hominoids. These insights are particularly valuable for paleontological reconstructions, where direct soft tissue evidence is often lacking. By establishing a relationship between skeletal traits and muscle volume, our study provides a framework for evaluating the accuracy of soft tissue reconstructions in hominoid species. This approach not only enhances our understanding of hominoid anatomy but also offers new avenues for exploring the functional morphology of extinct taxa.