Journal of Morphology最新文献

The amniote neck has evolved extensive mobility and this has contributed to functional and ecological diversification across the clade. Among amniotes, extant birds exhibit an S-shaped neck with multiple flexion points and displays significant variation in vertebral counts and morphology, enabling diverse foraging and feeding behaviors. While avian neck flexibility has increasingly attracted attention in ethology and functional morphology in recent years, its evolution within the archosaur lineage leading to birds remains unclear. Here, we quantified the ratio of the lever lengths (RLL) of selected muscles in the presacral vertebrae of extant crocodilians and birds as an index of joint rotation efficiency. Both crocodilians and birds display high RLL values at vertebral joints near the skull and the cervico-thoracic transition, suggesting that the functional cervical region lies anterior to the latter joint in both clades. In crocodilians, the position of this posterior high RLL joint varies among major lineages, implying that differences in cervical vertebral counts may be linked to lineage specific feeding ecologies. In contrast, birds possess an additional cervical region with high RLL values between the two major high RLL joints. This mid-posterior cervical subregion appears to be an avian evolutionary novelty that enhances rotational efficiency and likely facilitated the evolution of the highly flexible, multi-point bending neck unique to birds.

This review applied the two-joint link model to review the functional roles of femoral biarticular, monoarticular and lower leg muscles during walking in domestic cats, with comparative insights from dogs, horses and humans. Electromyographic (EMG) data from the right hindlimb were analyzed to characterize sequential activity switches and coactivation patterns among e-series and f-series muscles. In cats, extensive stance-phase activation of both groups including M. gluteus muscles (f1), M. biceps femoris (f3) and M. vastus muscles (e2) contrasted with humans, in whom f-series activity was minimal and the gastrocnemius (f1) was primarily active during the swing phase. Cross-species comparisons revealed consistent coactivation between two biarticular muscles (e3/f3) or between biarticular and monoarticular muscles (e3/e2), indicating functional parallels in redirecting forces at the ankle. In quadruped cats, dogs and horses, persistent M. gluteus muscle (f1) activity contributed to hip extension and hindlimb propulsion, highlighting its more prominent stance-phase role compared with humans. Mapping muscle activity onto six-sector force outputs demonstrated the model's capacity to interpret directional control of locomotion via combined muscle forces. Collectively, these findings refined the two-joint link model's applicability across tetrapods and provided a foundation for testable hypotheses regarding muscular coordination, limb segment stabilization and evolutionary adaptations in tetrapod locomotion.

The present histological, autoradiographic, and immunohistochemical study describes the maturation of caudal vertebrae and the origin of autotomous planes in the embryo of the lizard Anolis lineatopus. Autotomous vertebrae associated with connective planes for the detachment of the tail ensure higher survival chances for lizards. The study on late embryonic and pre-hatching stages shows that caudal vertebrae are largely colonized by hemopoietic cells and are not completely surrounded by compact bone laminae in some small areas. The periosteum surrounding the vertebral centrum and neural arch is not continuous, so that the spinal cord contacts through the meninges the veins inside the bone marrow of vertebral bodies. The formation of an alamellar bone outlining completely the vertebrae, as observed in adult lizards, is likely reached sometime after hatching. Discontinuities in the thin alamellar bone outlining the vertebrae are observed in the split or autotomous plane and in the foramen of spinal nerves. The chemical signal for the localization of the split is unknown. Tritiated thymidine autoradiography and 5BrdU-immunolabeling indicate that some periosteum osteoblasts surrounding the centrum and neural arches are proliferating in these late developmental stages, in addition to sclerotomic cells invading the inter-centrum. The remodeling process also includes the formation of a split plane due to the penetration of osteoblasts into the initial alamellar bone and the separation of the borders of the alamellar bone where proliferating osteoblasts are present. These cells also contain matrix metalloproteinaes and alkaline phosphatase, indicating that they are involved in remodeling the bones of caudal vertebrae during vertebral development, but likely also after hatching. Vertebrae therefore contain a large mass of bone marrow which stem cells can be liberated on the tail stump after tail autotomy, providing hematogenous cells that contribute to the initial formation of the blastema together mesenchymal cells and fibroblasts.

Echiurids, as nonsegmented annelids, have an excretory system of a special organization. The excretory system of the echiuran worms is known to consist of ultrafiltration zones on blood vessels and anal sacs. Prior to this study, the fine structure of the anal sacs had been described in detail only for Thalassema thalassemum (Thalassematinae). In contrast, the more complex anal sacs of Bonelliinae, which contain additional structural elements such as tubules, remained unexplored. This study describes the anatomy, histology, and ultrastructure of the anal sacs of Bonellia viridis Rolando, 1822 (Bonelliinae) using a set of modern morphological methods: computer microtomography, araldite histology, scanning and transmission electron microscopy. New data suggest functional implications for structural elements of the anal sacs: the conical part and the neck of the funnel, the tubules, and the end sac. The ciliary funnels are responsible for collecting filtrate to their conical parts and can close at their base, thus preventing reverse flow. According to the ultrastructural data, the inner epithelium of the tubules and the end sac modifies the incoming filtrate in two ways. The inner epithelium of the tubules carries out pinocytosis and accumulates electron-dense granules. The inner epithelium of the end sac has a basal labyrinth consisting of basal processes with numerous mitochondria extending deep into the extracellular matrix and indicates active ion transport. Additional zones responsible for ultrafiltration were identified in the outer epithelium of the anal sac—specifically within the tubule and at the base of the funnel. The origin of the echiurid anal sacs as a result of fusion and multiplication of the metanephridia at the posterior growth zone of metameric annelid-like ancestor is suggested.

Micromorphism represents a distinctive evolutionary adaptation in certain extinct and extant brachiopods. Previous anatomical studies of micromorphic brachiopods have primarily focused on the reproductive system structure or provided only general descriptions of the skeleton and the morphology of the lophophore. Here, we present a detailed morphological analysis of the micromorphic brachiopod Phaneropora galatheae Zezina, 1981, in the context of its miniaturization. Using histological techniques and micro-computed tomography, we describe the structure of the lophophore and its coelomic system, digestive, muscular, reproductive, and excretory systems. The anatomical organization of Ph. galatheae reveals a combination of juvenile features consistent with a possible paedomorphic origin, alongside modifications indicating the compact arrangement of internal organs associated with miniaturization.