Quel devenir pour les collections anatomiques en fluide ? Une approche historique

Aujourd’hui, la mise en évidence du danger potentiel de certaines solutions de conservation alcooliques ou à base d’aldéhyde, risque de mettre en péril le devenir des collections en fluides : pourtant des procédés de substitutions, autrefois jugés peu satisfaisants, représentent dorénavant des solutions aux problèmes actuels d'hygiène et de sécurité et de conservation des collections

Bite Force in the Extant Coelacanth Latimeria: The Role of the Intracranial Joint and the Basicranial Muscle

SummaryThe terrestrialization process involved dramatic changes in the cranial anatomy of vertebrates. The braincase, which was initially divided into two portions by the intracranial joint in sarcopterygian fishes, became consolidated into a single unit in tetrapods and lungfishes [1–3]. The coelacanth Latimeria is the only extant vertebrate that retains an intracranial joint, which is associated with a unique paired muscle: the basicranial muscle. The intracranial joint has long been thought to be involved in suction feeding by allowing an extensive elevation of the anterior portion of the skull, followed by its rapid depression driven by the basicranial muscle [4–7]. However, we recently challenged this hypothesis [8, 9], and the role of the basicranial muscle with respect to the intracranial joint thus remains unclear. Using 3D biomechanical modeling, we show here that the basicranial muscle and the intracranial joint are involved in biting force generation. By flexing the anterior portion of the skull at the level of the intracranial joint, the basicranial muscle increases the overall bite force. This likely allows Latimeria to feed on a broad range of preys [10, 11] and coelacanths to colonize a wide range of environments during their evolution [4]. The variation in the morphology of the intracranial joint observed in Devonian lobe-finned fishes would have impacted to various degrees their biting performance and might have permitted feeding specializations despite the stability in their lower jaw morphology [12].Video Abstrac

Gestion et étude des restes humains en fluides

Les restes humains sont présents dans les collections du Muséum national d’histoire naturelle de Paris depuis sa création. Depuis toujours, ces pièces ont constitué un support pour l’enseignement, un matériel essentiel pour la recherche et, bien sûr, des pièces incontournables dans les présentations muséales. Par conséquent, une attention particulière doit être portée à ces collections, le bien-fondé d’une collection étant qu’elle doit servir pour être pleinement valorisée.Human remains have been part of the collections of the Muséum National d’Histoire Naturelle, Paris, since it was founded. These items have always been used for teaching purposes, provided basic material for research, and, of course, been put on display in the museum. Consequently, particular attention must be paid to these collections, the legitimacy of a collection being that its potential should be fully exploited

Les techniques d’imagerie 3D au service de la valorisation scientifiques des collections anatomiques

La présentation de cette étude virtuelle de l’anatomie d’un spécimen de cœlacanthe réalisée grâce à l’utilisation de l’imagerie tridimensionnelle par rayons X et par résonance magnétique met notamment en évidence les possibilités d’application de ces technologies – qui évitent les manipulations répétitives et préservent l’intégrité morphologique des spécimens précieux et scientifiquement importants – dans le domaine de la scénographie ou celui de la conservation préventive.The presentation of this virtual study of the anatomy of a Coelacanthe specimen produced using three dimensional x ray imaging and magnetic resonance notably brings light to the possibilities of application of these technologies – which avoid repetitive manipulations and preserve the morphological integrity of precious and scientifically important specimens – in the field of scenography or of preventive conservation.f

Revision of the muscular anatomy of the paired fins of the living coelacanth Latimeria chalumnae (Sarcopterygii: Actinistia)

peer reviewedAs a sarcopterygian fish, the extant coelacanth Latimeria has muscular paired fins, different in their skeletal and muscular anatomy from the paired fins of actinopterygians. Although the muscular anatomy of the pectoral and pelvic fins of Latimeria has been described by several studies, a detailed functional description of the muscles and their architecture has never been performed. Our detailed functional description of the muscles of the paired fins shows a more complex organization than previously described. The pectoral and pelvic fins have a different organization of their muscular anatomy, and the pelvic fin shows a more plesiomorphic configuration of the muscles since most of them are poly-articular and run from the pelvic girdle to the fin rays, an organization typical of actinopterygians. We found that the pectoral fins are stronger than the pelvic fins which is likely to be associated with the greater contribution of the pectoral fins to locomotion and manoeuvring. Finally, the study of the joint mobility of the paired fins showed that the pectoral fins show greater mobility than the pelvic fins. The reduced mobility of the pelvic fin is possibly a consequence of the morphology of the mesomeres and the large pre-axial radials

Neurocranial development of the coelacanth and the evolution of the sarcopterygian head

The neurocranium of sarcopterygian fishes was originally divided into an anterior (ethmosphenoid) and posterior (otoccipital) portion by an intracranial joint, and underwent major changes in its overall geometry before fusing into a single unit in lungfishes and early tetrapods. Although the pattern of these changes is well-documented, the developmental mechanisms that underpin variation in the form of the neurocranium and its associated soft tissues during the evolution of sarcopterygian fishes remain poorly understood. The coelacanth Latimeria is the only known living vertebrate that retains an intracranial joint. Despite its importance for understanding neurocranial evolution, the development of the neurocranium of this ovoviviparous fish remains unknown. Here we investigate the ontogeny of the neurocranium and brain in Latimeria chalumnae using conventional and synchrotron X-ray microcomputed tomography as well as magnetic resonance imaging, performed on an extensive growth series for this species. We describe the neurocranium at the earliest developmental stage known for Latimeria, as well as the major changes that the neurocranium undergoes during ontogeny. Changes in the neurocranium are associated with an extreme reduction in the relative size of the brain along with an enlargement of the notochord. The development of the notochord appears to have a major effect on the surrounding cranial components, and might underpin the formation of the intracranial joint. Our results shed light on the interplay between the neurocranium and its adjacent soft tissues during development in Latimeria, and provide insights into the developmental mechanisms that are likely to have underpinned the evolution of neurocranial diversity in sarcopterygian fishes

La conservation des collections en fluide

The conservation of collections held in fluids, a conservational and historical approach Knowledge of the history of collections held in fluids is very important, as it enables researchers to determine with chemicals were used at the time of the original conservation. It is hence possible to know whether the pieces were fixed or simply immersed into a preservative, which will be insufficient to prevent deterioration and the eventual disappearance of the collection. This will also facilitate the measures necessarily taken to protect specific cases before any intervention takes place

A 'no-threshold' histogram-based image segmentation method

Although most histogram-based image segmentation methods rely on the identification of a good threshold, we show that thresholding is not mandatory. Instead, we propose the association of grades of membership to each individual pixel, in order to perform probabilistic relaxation in the image space (which realizes some kind of regularization) and finally to obtain the segmented image through defuzzy fication of the relaxed grades of membership