Journal of Anatomy最新文献

Cover image: The head of an air-breathing swamp eel, Monopterus albus (top), and its vascular cast (below). See A. Ishimatsu et al., ‘Comparison of the respiratory vasculature of two species of swamp eels, Monopterus albus and Ophisternon bengalense (Synbranchidae)’, this issue.

This review celebrates the work of Professor Mike Benjamin, whose anatomical research transformed our understanding of entheses - the sites where tendons, ligaments and other connective tissues attach to bone. This review aims to provide an overview of Professor Benjamin's foundational concepts, including the enthesis organ, functional entheses and the synovio-entheseal complex and their relevance to musculoskeletal health and disease. Entheses are biomechanically complex regions that accommodate the transition between compliant soft connective tissues and rigid bone by natural macroscopic and microscopic adaptations that reduce stress concentration. Macroscopically, tendons and ligaments often flare near their attachment sites, increasing surface area. Microscopically, entheses are classified as fibrous or fibrocartilaginous, with the latter displaying a zonal organisation that includes uncalcified and calcified fibrocartilage. These zones provide a graded transition in stiffness, reducing the risk of tissue failure and enables gradual bending of collagen fibres. Mechanical loading is essential for the normal development of the enthesis and is required to maintain its biomechanical properties in the adult. The enthesis organ concept, one of Professor Benjamin's most significant contributions, recognises that entheses are rarely isolated structures. Instead, they are part of a functional unit comprising adjacent tissues including sesamoid and periosteal fibrocartilages, bursae, fat pads and retinaculae which collectively dissipate mechanical stress. Adipose tissue and synovium at these sites may also play immunological and proprioceptive roles, and its involvement in neurovascular invasion has implications for pain and pathology. However, beyond direct tendon-bone attachments, functional entheses describe regions where tendons and ligaments interact with bone at a distance from the insertion but share structural and functional characteristics with classical entheses. The development of these concepts highlights Professor Benjamin's integrative approach to research and will continue to underpin research in musculoskeletal biology, pathology and tissue engineering, as well as inspire generations of anatomists.

The origin and evolution of snakes has been marked by the acquisition of many morphological and functional novelties, one of which is the possession of a highly kinetic skull allowing for the consumption of prey that are often larger than their head diameter. One feature of the iconic wide gape of macrostomate (large-mouthed) snakes is due to changes in the rostral midline where the left and right hemi-mandible come together. Across vertebrates, the two sides of the lower jaw are held together by the mandibular symphysis. In snakes, the two halves of the lower jaw do not fuse and the symphysis remains free, facilitating gape expansion. The symphysis has previously been explored in lizards and crocodiles, where ligamentous fibres and cartilages span the joint. Here, we compared the anatomy of the forming 'free' mandibular symphysis in the corn snake (Pantherophis guttatus) to symphysis development in two lizards, the veiled chameleon (Chamaeleo calyptratus) and the ocelot gecko (Paroedura picta), and an outgroup sauropsid, the chicken (Gallus gallus domesticus). Microcomputed tomography imaging, whole-mount skeletal staining and histology staining confirmed the absence of bone and cartilage fusion at the mandibular symphysis in the corn snake during development, in contrast to the complete fusion of cartilage, but not bone, in both lizards and the fusion of the bone in the chick. Trichrome staining under circular polarised light and whole fast green staining highlighted that, while the symphyseal region was populated by a dense network of collagen fibres, the snake hemi-mandibles were not connected across the rostral region by this fibrous network. Instead, collagen fibres extended backwards and around the snake mental groove to an intermandibular nodule. This nodule attached to the midline dorsally, allowing integration of the movement of the soft and hard tissues. Our analysis highlights the adaptations required to allow extreme lower jaw mobility and independence of the two sides of the jaw as found in macrostomate snakes.

The study of development provides valuable information on the evolution of morphological traits, enabling the detection of important evolutionary processes and revealing unique ontogenetic characteristics not observed in adult individuals. The Characiformes is one of the largest groups of Neotropical fish and includes several lineages of small species that have undergone a reduction in body size, a phenomenon often associated with paedomorphosis. In this study, we analyzed an ontogenetic series of a small characiform, Inpaichthys kerri, ranging from newly hatched individuals to adults, with the aim of describing in detail the development of the cranial skeleton and establishing its ossification sequence. Seventy-two skull bones were described, from the first signs of ossification to their adult forms, including the complete sequence of appearance of these structures throughout development. We also identified a unique developmental sequence for the infraorbital bones of I. kerri. We highlight the presence of paedomorphic characters found in I. kerri, which are shared by its congeners and by other small Characiform lineages, and discuss them based on ontogenetic and phylogenetic information. The information collected and discussed here is unprecedented and is valuable to the understanding of relationships within Acestrorhamphidae.

The thenar and hypothenar muscles of the hand have origins on the transverse carpal ligament (TCL). Understanding the morphological distribution of this muscle-ligament interaction has clinical and biomechanical benefits. Robot-assisted ultrasonography was used to reconstruct the three-dimensional TCL volar surface and TCL-muscle interface in ten cadaveric specimens. The interface areas and radial-ulnar length at discretized proximal-distal tunnel levels were calculated. The total area of the TCL volar surface was 457.4 ± 62.2 mm². The TCL-thenar and TCL-hypothenar interface areas were 142.3 ± 38.0 mm² (30.8 ± 6.6%) and 32.3 ± 22.4 mm² (7.0 ± 4.7%), respectively. The TCL area not interfaced by the thenar or hypothenar muscles was 282.72 ± 40.8 mm² (62.1 ± 7.4%). The relative radial-ulnar TCL-muscle interface length was significantly dependent upon muscle group (p < 0.001) and proximal-distal carpal tunnel level (p < 0.001). The maximum percentage of the radial-ulnar length of the TCL volar surface occupied by the TCL-thenar and TCL-hypothenar interface was 57.0 ± 9.9% and 15.5 ± 9.6%, respectively. Quantification of the three-dimensional muscle coverage distribution on the TCL can help to advance anatomical understanding, inform biomechanical mechanisms for utilizing the muscle-ligament interaction, and minimize potential functional disruption of carpal tunnel release.

The dermal skeleton appeared early in vertebrate evolution in the form of mineralized skin denticles composed of tooth-like units-odontodes. This surface odontogenic competence later also expanded inside the oropharyngeal cavity where teeth are formed as modified odontodes possessing innovative replacement dynamics. Whereas in modern cartilaginous fishes, both the internal odontodes (teeth) and external odontodes (scales) exhibit generally the same shape and structure, the dermal skeleton of bony fishes was further modified by the fusion of odontodes forming so-called odontocomplexes. This ancient dermal armour was reduced in both ray-finned and lobe-finned fishes, or disappeared in tetrapods. Bichirs (Polypteridae) occupy a key phylogenetic position as the earliest extant ray-finned fishes retaining a massive dermal skeleton. We performed developmental and structural analyses of their odontocomplex elements comprising the cranial dermal bones, trunk scales, fin rays, and spines of the dorsal finlets, primarily using the Senegal bichir (Polypterus senegalus). All these elements are covered by a hypermineralised layer ganoine, considered to be a true enamel. Yet, during the development of these odontocomplex elements, individual odontodes could not be recognised. However, we also identified one unique dermal element with a dual structural nature combining the scale-like odontocomplex with individual odontodes. These so-called dental plates form a narrow series of repeating elements that extend in between the fin rays on bichir pectoral fins. Individual odontodes on these dental plates are organised into C-shaped rows attached to a scale-like element. Interestingly, these individual odontodes bear striking morphological and histological similarities to teeth, and their dynamics of replacement parallel that of teeth in bichir oral dentition. Dental plates occupy a distinct dermal skeletal domain on distal pectoral fins, where replacing odontodes form a spiky surface with apparent functional advantages when bichirs rest their pectoral fins upon the substrate.

Whilst many birds glide briefly with wings held horizontally, some species maintain this posture for extended periods during soaring. This is considered possible because of the contraction of the m. pectoralis that holds the wing in place, although albatrosses seem to have a physical shoulder lock that helps with this action. However, studies of this flight style have not considered the cranially orientated long-axis rotation of the humerus induced by the contraction of the main flight muscles that would depress the ulna and change the angle of the aerofoil downwards. This study explored whether the m. deltoideus major helps counteract this rotation. Muscle masses were collated from the literature and from dissections of birds to allow exploration of the allometry of muscle masses versus body mass. All muscles exhibited isometry with body mass, but relative to the size of the m. pectoralis, the m. deltoideus major was large but only in a few species that regularly soar or glide for long periods. By contrast, other elevator muscles were less variable among species. The presence of relatively large deltoideus major muscles in soaring species was suggestive that this muscle, since it originates on the scapula extending caudally and inserting on the dorsal humerus, may counteract humeral long-axis rotation around its longitudinal axis during contraction of the breast muscles. The results of this study are suggestive of previously unconsidered substantial roles for other muscles of the pectoral girdle and forelimb during different flight styles in birds.

Within Avemetatarsalia, postcranial skeletal pneumaticity (PSP) occurs in pterosaurs, as well as theropod (including extant Aves) and sauropod dinosaurs. However, the evolutionary origins of PSP in the latter clade remain largely unknown, with few studies assessing species closely related to, but outside, the sauropod radiation, that is, early-branching sauropodomorphs. Furthermore, most proposed identifications of PSP in early-branching sauropodomorphs relate to external indicators of internal pneumaticity, for example, the presence of vertebral subfossae. To address this deficit, we CT scanned representative elements from the vertebral columns of the early-branching sauropodomorphs Thecodontosaurus antiquus, Pantydraco caducus, Ruehleia bedheimensis and Plateosaurus longiceps, all from the Late Triassic of Europe. These new data were compared with the small number of early-branching sauropodomorphs with published vertebral CT scan data, namely the Late Triassic Brazilian species, Buriolestes schultzi, Pampadromaeus barberenai and Macrocollum itaquii. Based on the sampled vertebrae, PSP is absent in Buriolestes, Pampadromaeus, Pantydraco and probably Thecodontosaurus. It is possible that the neural arches of the posterior cervical vertebrae of Thecodontosaurus possess PSP, but this can only be interpreted from broken transverse cross-sections and not CT scans. The posterior cervical vertebrae of Ruehleia possess PSP in the neural arches; however, their corresponding centra, along with the centra and neural arches of the anterior–middle dorsal vertebrae, are apneumatic. Plateosaurus possesses PSP in the neural arches of the middle cervical vertebrae through to the middle dorsal vertebrae, whereas the presacral centra are apneumatic. Where present, pneumatic internal chambers are neither exclusively camerate nor camellate, nor do they align with the ‘protocamerate’ bone structure previously described in the posterior cervical and anterior dorsal vertebrae of Macrocollum. From external indicators, PSP might be present in the sacral neural arches of Ruehleia and Plateosaurus but is absent in the caudal vertebrae. However, our results reveal that PSP cannot be unambiguously determined from external indicators; subfossae do not always communicate with internal chambers; and internal chambers sometimes communicate with undivided fossae. PSP in early-branching sauropodomorphs probably evolved first in the neural arches of the posterior cervical vertebrae, expanding anteriorly and posteriorly along the vertebral column. Furthermore, the distribution of PSP in Late Triassic early-branching sauropodomorphs does not appear to be correlated with body size. Finally, our results lend support to the idea that pterosauromorphs, theropods and sauropodomorphs evolved PSP in the Late Triassic independently of each other.

Cerebral palsy (CP) is a neurological disorder caused by a non-progressive lesion in the developing fetal or infant brain associated with structural muscle alterations. Despite its relevant function in walking, the semitendinosus (ST) structure has been poorly investigated in CP, especially in (very) young children, although this could help determine early events and whether these alterations differ between age groups. This study aimed at defining the histological characteristics of the ST muscle in very young (preschool age group: 3-5 years old) and young (school age group: 6-9 years old) ambulant children with CP, in comparison to age-matched typically developing (TD) children. Microbiopsies of ST were collected in 37 children with CP and 33 TD children (preschool: 15 CP, 9 TD; school age: 22 CP, 24 TD). Muscle cross-sections were immunostained with (1) myosin heavy chain (MHC-I, MHC-IIa, and MHC-IIx) to determine fiber cross-sectional area (absolute: afCSA and normalized to total lower leg length: nfCSA), fiber proportion, (2) CD31 combined with MHC to assess capillary density, capillary to fiber ratio, capillary domain, and heterogeneity index, and (3) Pax7 to quantify the number of satellite cells. fCSA intrasubject variation was determined by coefficient of variation (CV). None of the parameters were altered in the preschool age CP compared to TD, except for larger type I afCSA in girls compared to boys. For the school-age group, type IIx afCSA (+21%, p = 0.019), nfCSA of all fibers (+48%, p = 0.03), and type IIa (+32%, p = 0.019) were larger in CP, and type IIx proportion was higher (+91%, p = 0.016) compared to TD. There was also an increased CV (all fibers: +30%, p = 0.005; type I: +32%, p < 0.001; IIa: +38%, p = 0.025). Satellite cell number and capillarization remained unaltered. These results indicate that the ST appears unaffected in very young ambulant CP children, but alterations develop with age.

In female vertebrates, the pelvis plays a role in important biological processes including reproduction and locomotion, and its evolution is thus likely influenced by multiple selective pressures. Here, we used CT scans, 3D geometric morphometrics, and phylogenetic comparative methods to describe the evolution of the female pelvis of Sceloporus lizards, and to tease apart the relative importance of the evolution of live-bearing, arboreality, and allometry in altering pelvis shape. We found that the ancestral egg-laying species tended to exhibit dorsoventrally tall female pelvises, and that two of three clades of live-bearing Sceloporus evolved both larger body sizes and dorsoventrally flat, laterally wide female pelvises. Larger body sizes may have relaxed constraints on pelvis height, allowing these mostly terrestrial and rock-dwelling species to respond to selective forces that enhance crypsis or thermoregulation by evolving dorsoventrally flatter and laterally wider pelvises. In contrast, one large clade of live-bearing and arboreal species had dorsoventrally tall pelvises, like those of the ancestral egg-laying species. Again, evolutionary shifts to larger body sizes may have relaxed allometric constraints, allowing adaptive responses to arboreality that converge on those of terrestrial egg-layers. Further studies are needed in other taxa to determine the importance of larger body sizes and consequently relaxed allometric constraints in shaping other morphological features.