Cranial Muscles Research Articles

Limb Morphology in the Macaroni Penguin (Eudyptes chrysolophus) Exhibits Adaptations for Both Sub‐aqueous Flying and Locomotion on Land

Requiring both wing‐propelled swimming and rugged overland locomotion, Macaroni penguins possess highly specialized morphology in both limbs. We dissected both the wing and hindlimb of one female and one male macaroni penguin. The distal wing exhibits very reduced musculature, and only retains very small brachialis and dorsal ulno‐metacarpal muscles. The elbow and metacarpal joints exhibit significantly decreased mobility compared to other birds. Proximal extrinsic wing muscles extend long tendons into the distal wing to control the dorso‐ventrally flattened flipper. Two sesamoid bones at the elbow joint provide a main attachment point for the proximal musculature, and probably contribute to the stiffening of the wing during underwater propulsion. The enlarged and extended sternum houses an extensive pectoralis muscle, responsible for the downstroke, which comprises nearly the entire ventral body wall. Supracoracoideus, found anatomically deep to pectoralis major and responsible for the upstroke, weighed about half of the pectoralis muscle, unlike most birds, where supracoracoideus weighs only about one‐fifth. An enlarged supracoracoideus increases the strength of the upstroke against viscous water. The tendons of latissimus dorsi cranialis and caudalis pass through a fibrous trochlea extending from the triceps complex to attach to the humerus, and possibly increases wing forces when moving the wing caudally. Unlike the sparse wing musculature, extensive leg musculature comprises about half of the dorsal body wall. The sartorius muscle, the most cranial hindlimb muscle, lies cranial to the caudal edge of the scapula, and cranial to the caudal margin of the sternum. Despite this, penguins exhibit restricted mobility during locomotion on land including apparent reduced range of motion in the knee joint, which contributes to their signature waddle. In addition, both Macaroni penguin specimens possess a unique muscle we have named the adductor tibialis. This muscle extends from the tibia of one hindlimb, across the midline where it slightly connects to the sternum, and attaches to the tibia of the contralateral limb, effectively tying the hindlimbs together. This permanent adduction probably helps create a streamlined figure while swimming to create faster speeds. In contrast to the knee, the penguin can greatly extend and flex the tarsus during locomotion. The considerable extensor system in the tarsus helps the penguin cross different terrains while walking, as well as give them the ability to jump.

African Wild Dogs (Lycaon pictus) Show Adaptations to Sociality and Hypercarnivory in Their Cranial Musculature

African wild dogs (Lycaon pictus) are highly social canids that live in large, hierarchical packs and engage in coordinated hunts. Recent research has suggested that enlarged muscles associated with expressive movement of the eyes and eyebrows may have evolved in domestic dogs (Canis familiaris) to facilitate interspecies communication with their human owners. In L. pictus, communication is reported to occur predominantly through vocalization with reduced reliance on facial expressions; however, the mimic muscles in L. pictus have never been described and evaluated. L. pictus is also hypercarnivorous with the highest documented bite force quotient of any mammalian carnivore. It has large, mobile ears, which enhance its auditory capabilities while hunting and assist with thermoregulation.We performed detailed dissections of the muscles of facial expression, mastication, and auricular movement in an adult male L. pictus,and conducted diffusible iodine‐based contrast‐enhanced computed tomographic (diceCT) scans of the head. Musculus levator anguli oculi medialis (LAOM) and retractor anguli oculi lateralis (RAOL), muscles of hypothesized importance in domestic dog‐human non‐verbal communication, are enlarged in L. pictus, suggesting that ocular expressions represent a significant component of communication. LAOM exhibits an intricate relationship with adjacent orbital musculature including partial fusion along its borders with mm. orbicularis oculi and frontalis. Muscles that draw the angles of the mouth caudally (e.g., m. zygomaticus major) are expanded. Numerous ramifying branches of CN VII and CN V2 course across the face to provide extensive sensory and motor innervation. These findings indicate that facial expression musculature of African wild dogs is well‐equipped for non‐verbal communication and that the same adaptations argued to facilitate communication between domestic dogs and humans may also facilitate intraspecific communication in L. pictus.Muscles of mastication are especially enlarged in L. pictus, with multiple bellies of mm. masseter and temporalis separated by deep layers of thick intermuscular fascia and with expanded insertions onto the mandible. Musculus digastricus is composed of a single, large belly without intervening tendon, and it receives its innervation exclusively from CN V3. These enlargements reflect increased masticatory capabilities in L. pictus, which enable its powerful bite force and hypercarnivorous diet. Auricular muscles are also well‐developed, supporting greater leverage and fine manipulation of its large, mobile ears. Musculus frontoscutularis is well‐developed and distinctly separable from m. frontalis, suggesting greater leverage of the auricle via attachments to the scutiform cartilage. The intrinsic ear muscles differ in pattern and orientation from all other published canids, demonstrating unique muscular control over rotation and fine manipulation of the auricle. Taken together, these morphological patterns illustrate that specific adaptations in the cranial musculature of L. pictus facilitate its ecological habits.

Evolutionary Innovations of the Feeding Apparatus in Herbivorous Dinosaurs

Although most studies in feeding biology of non‐avian dinosaurs have investigated feeding function and ecology in carnivorous dinosaurs, the complex diversity of feeding in herbivorous dinosaurs has recently been explored in much greater detail. Herbivorous non‐avian dinosaurs, composed of nearly all sauropodomorphs and ornithischians as well as a few theropod groups (i.e., ornithomimosaurs, therizinosaurs, and oviraptorosaurs), show a wide range of craniomandibular feeding mechanisms, each with unique adaptations for processing various forms of plant‐life. Here, I will review over a century of feeding studies in herbivorous dinosaurs, with particular focus on more recent advancements in our knowledge of their feeding evolution and ecology. These studies have primarily focused on the many components influencing the functional morphology of the head and neck of these animals, including: dental morphology, with studies in dental microwear and macrowear, overall morphological analysis of the skull and cervical vertebrae, reconstruction of cranial musculature and other soft tissues of the head, and biomechanics of the skull, with comparative analyses of mechanical advantage of the jaw system and 3D computer modeling in the form of finite element analyses and multibody dynamics analyses with the use of laser scans and CTs of dinosaur skulls. All these studies are instrumental in our understanding of the evolution and diversity of bite forces as well as feeding mechanisms that range from orthal to palinal feeding motions as well as bilateral hemi‐mandibular long‐axis rotation (especially in a variety of ornithischians). The similarities and differences between herbivorous dinosaurs and the herbivores of today (especially mammalian megaherbivores) show a great deal about how evolutionary opportunities and constraints have made a significant impact on the diverse nature of herbivory and its importance in ecosystems around the world.

Speech-induced action myoclonus

BackgroundSpeech-induced action myoclonus may occur as a component of a generalized myoclonus syndrome. However, it may also present in isolation, or with a paucity of other findings, and be diagnostically challenging. ObjectivesTo report a retrospective case series of restricted speech-induced action myoclonus. MethodsWe reviewed cases of speech-induced action myoclonus evaluated at Mayo Clinic Rochester from 1989 to 2020. We eliminated cases where a more generalized myoclonic disorder was also present. Clinical, imaging, and electrophysiologic data were extracted. ResultsFour cases were identified in which speech-induced action myoclonus of craniofacial muscles was the predominant clinical presentation. All described cranial muscle twitching induced by speaking, and two cases also reported speech interruptions. Diagnosis was confirmed by expert speech pathologists in all cases. Diagnostic aids included modulation with different speech tasks and speaking rates, and surface electrophysiology which confirmed craniofacial myoclonus induced by speaking tasks (three cases). Previous misdiagnosis included functional, dystonic, neuromuscular junction pathology, or hemifacial spasm. Two cases had isolated speech-induced myoclonus, and the other two had coexistent upper limb tremor. Potential etiologic factors were identified in three cases – medication (2), epilepsy (1) – while in one patient no cause was identified. One patient partially improved with anti-myoclonic medication and speech therapy. ConclusionsSpeech-induced action myoclonus may occur in isolation and is frequently misdiagnosed. Diagnostic aids include modulation with different speech tasks and speaking rates, and surface electrophysiology.

Case study of a rare occipital osteoma related to cranial trauma.

Burial 280 is a 31- to 40-year-old male Native American individual who lived in a 10th to 16th century coastal foraging society in California. His remains display a large ectocranial elevation on the occipital, measuring 23.3 mm anteroposteriorly, 25.3 mm mediolaterally, and is elevated to 20.1 mm. It is located along the superior nuchal line on the left side of the occipital and represents an extremely rare occipital localization of a particular type of trauma-related osteoma. In our prior study of Burial 280, trauma etiology was not considered; herein, we present evidence for such a cause. Such trauma-related neoplasms are sometimes called ballooned (or giant, depending on size) osteomas. The presence of this tumor appears to have resulted in asymmetrical cranial muscle use and consequent skeletal changes. This case study illustrates that cranial trauma may sometimes induce benign tumor elevations, rather than a depression or pronounced fracture.

A new conceptual framework for the musculoskeletal biomechanics and physiology of ray-finned fishes.

ABSTRACTSuction feeding in ray-finned fishes requires substantial muscle power for fast and forceful prey capture. The axial musculature located immediately behind the head has been long known to contribute some power for suction feeding, but recent XROMM and fluoromicrometry studies found nearly all the axial musculature (over 80%) provides effectively all (90–99%) of the power for high-performance suction feeding. The dominance of axial power suggests a new framework for studying the musculoskeletal biomechanics of fishes: the form and function of axial muscles and bones should be analysed for power production in feeding (or at least as a compromise between swimming and feeding), and cranial muscles and bones should be analysed for their role in transmitting axial power and coordinating buccal expansion. This new framework is already yielding novel insights, as demonstrated in four species for which suction power has now been measured. Interspecific comparisons suggest high suction power can be achieved in different ways: increasing the magnitude of suction pressure or the rate of buccal volume change, or both (as observed in the most powerful of these species). Our framework suggests that mechanical and evolutionary interactions between the head and the body, and between the swimming and feeding roles of axial structures, may be fruitful areas for continued study.

Neoplastic nerve lesions.

Though metastasis and malignant infiltration of the peripheral nervous system is relatively rare, physicians should have a familiarity with their presentations to allow for prompt diagnosis and initiation of treatment. This article will review the clinical presentations, diagnostic evaluation, and treatment of neoplastic involvement of the cranial nerves, nerve roots, peripheral nerves, and muscle. Due to the proximity of the neural structure traversing the skull base, metastasis to this region results in distinctive syndromes, most often associated with breast, lung, and prostate cancer. Metastatic involvement of the nerve roots is uncommon, apart from leptomeningeal carcinomatosis and bony metastasis with resultant nerve root damage, and is characterized by significant pain, weakness, and numbness of an extremity. Neoplasms may metastasize or infiltrate the brachial and lumbosacral plexuses resulting in progressive and painful sensory and motor deficits. Differentiating neoplastic involvement from radiation-induced injury is of paramount importance as it dictates treatment and prognosis. Neurolymphomatosis, due to malignant lymphocytic infiltration of the cranial nerves, nerve roots, plexuses, and peripheral nerves, deserves special attention given its myriad presentations, often mimicking acquired demyelinating neuropathies.

Cranial muscle reconstructions quantify adaptation for high bite forces in Oviraptorosauria

Oviraptorosaurians are an unusual and probably herbivorous group of theropod dinosaurs that evolved pneumatised crania with robust, toothless jaws, apparently adapted for producing a strong bite. Using 3D retrodeformed skull models of oviraptorid oviraptorosaurians Citipati, Khaan, and Conchoraptor, along with the earliest diverging oviraptorosaurian, Incisivosaurus, we digitally reconstruct jaw adductor musculature and estimate bite force to investigate cranial function in each species. We model muscle length change during jaw opening to constrain optimal and maximum gape angles. Results demonstrate oviraptorids were capable of much stronger bite forces than herbivorous theropods among Ornithomimosauria and Therizinosauria, relative to body mass and absolutely. Increased bite forces in oviraptorid oviraptorosaurians compared to the earliest diverging oviraptorosaurian result from expanded muscular space and different cranial geometry, not changes in muscular arrangement. Estimated optimal and maximum possible gapes are much smaller than published estimates for carnivorous theropods, being more similar to the herbivorous therizinosaurian theropod Erlikosaurus and modern birds. Restrictive gape and high bite force may represent adaptation towards exploiting tough vegetation, suggesting cranial function and dietary habits differed between oviraptorids and other herbivorous theropods. Differences in the relative strength of jaw adductor muscles between co-occurring oviraptorids may be a factor in niche partitioning, alongside body size.

Suction feeding biomechanics of Polypterus bichir: investigating linkage mechanisms and the contributions of cranial kinesis to oral cavity volume change.

Many fishes use substantial cranial kinesis to rapidly increase buccal cavity volume, pulling prey into the mouth via suction feeding. Living polypterids are a key lineage for understanding the evolution and biomechanics of suction feeding because of their phylogenetic position and unique morphology. Polypterus bichir have fewer mobile cranial elements compared with teleosts [e.g. immobile (pre)maxillae] but successfully generate suction through dorsal, ventral and lateral oral cavity expansion. However, the relative contributions of these motions to suction feeding success have not been quantified. Additionally, extensive body musculature and lack of opercular jaw opening linkages make P. bichir of interest for examining the role of cranial versus axial muscles in driving mandibular depression. Here, we analyzed the kinematics of buccal expansion during suction feeding in P. bichir using X-ray Reconstruction of Moving Morphology (XROMM) and quantified the contributions of skeletal elements to oral cavity volume expansion and prey capture. Mouth gape peaks early in the strike, followed by maximum cleithral and ceratohyal rotations, and finally by opercular and suspensorial abductions, maintaining the anterior-to-posterior movement of water. Using a new method of quantifying bones' relative contributions to volume change (RCVC), we demonstrate that ceratohyal kinematics are the most significant drivers of oral cavity volume change. All measured cranial bone motions, except abduction of the suspensorium, are correlated with prey motion. Lastly, cleithral retraction is largely concurrent with ceratohyal retraction and jaw depression, while the sternohyoideus maintains constant length, suggesting a central role of the axial muscles, cleithrum and ceratohyal in ventral expansion.

Upper body involvement in GNE myopathy assessed by muscle imaging

Upper body muscle involvement has never been systematically investigated in GNE myopathy (GNEM). Aims of our study were to explore upper body involvement in GNEM patients by means of muscle MRI, to compare the degree of pathology with that of lower body and to validate the MRI pattern of the lower limbs in novel patients. MRI scans of 9 GNEM patients were retrospectively evaluated. T1-weighted and short-tau inversion recovery images were scored. As a result, serratus anterior was involved in all patients, followed by subscapularis and trapezius muscles. The majority of scans consistently showed hypotrophy of pectoralis minor. Conversely, cranial muscles including the tongue were always spared while pectoralis major and latissimus dorsi were relatively spared. We confirmed the known pattern of involvement in the pelvic girdle and limbs, that were more significantly affected than the upper girdle in all disease stages. Paraspinal muscles were also frequently affected displaying both a cranio-caudal and latero-medial gradient of severity along the body axis. Upper girdle MRI highlights a selective muscle involvement in GNEM, offering an added value in patients’ diagnostic workup and deep stratification.

Elastic energy storage in seahorses leads to a unique suction flow dynamics compared with other actinopterygians.

ABSTRACTSuction feeding is a dominant prey-capture strategy across actinopterygians, consisting of a rapid expansion of the mouth cavity that drives a flow of water containing the prey into the mouth. Suction feeding is a power-hungry behavior, involving the actuation of cranial muscles as well as the anterior third of the fish's swimming muscles. Seahorses, which have reduced swimming muscles, evolved a unique mechanism for elastic energy storage that powers their suction flows. This mechanism allows seahorses to achieve head rotation speeds that are 50 times faster than those of fish lacking such a mechanism. However, it is unclear how the dynamics of suction flows in seahorses differ from the conserved pattern observed across other actinopterygians, or how differences in snout length across seahorses affect these flows. Using flow visualization experiments, we show that seahorses generate suction flows that are 8 times faster than those of similar-sized fish, and that the temporal patterns of cranial kinematics and suction flows in seahorses differ from the conserved pattern observed across other actinopterygians. However, the spatial patterns retain the conserved actinopterygian characteristics, where suction flows impact a radially symmetric region of ∼1 gape diameter outside the mouth. Within seahorses, increases in snout length were associated with slower suction flows and faster head rotation speeds, resulting in a trade-off between pivot feeding and suction feeding. Overall, this study shows how the unique cranial kinematics in seahorses are manifested in their suction-feeding performance, and highlights the trade-offs associated with their unique morphology and mechanics.

Branchiomeric Muscle Development Requires Proper Retinoic Acid Signaling.

The first and second branchiomeric (branchial arch) muscles are craniofacial muscles that derive from branchial arch mesoderm. In mammals, this set of muscles is indispensable for jaw movement and facial expression. Defects during embryonic development that result in congenital partial absence of these muscles can have significant impact on patients’ quality of life. However, the detailed molecular and cellular mechanisms that regulate branchiomeric muscle development remains poorly understood. Herein we investigated the role of retinoic acid (RA) signaling in developing branchiomeric muscles using mice as a model. We administered all-trans RA (25 mg/kg body weight) to Institute of Cancer Research (ICR) pregnant mice by gastric intubation from E8.5 to E10.5. In their embryos at E13.5, we found that muscles derived from the first branchial arch (temporalis, masseter) and second branchial arch (frontalis, orbicularis oculi) were severely affected or undetectable, while other craniofacial muscles were hypoplastic. We detected elevated cell death in the branchial arch mesoderm cells in RA-treated embryos, suggesting that excessive RA signaling reduces the survival of precursor cells of branchiomeric muscles, resulting in the development of hypoplastic craniofacial muscles. In order to uncover the signaling pathway(s) underlying this etiology, we focused on Pitx2, Tbx1, and MyoD1, which are critical for cranial muscle development. Noticeably reduced expression of all these genes was detected in the first and second branchial arch of RA-treated embryos. Moreover, elevated RA signaling resulted in a reduction in Dlx5 and Dlx6 expression in cranial neural crest cells (CNCCs), which disturbed their interactions with branchiomeric mesoderm cells. Altogether, we discovered that embryonic craniofacial muscle defects caused by excessive RA signaling were associated with the downregulation of Pitx2, Tbx1, MyoD1, and Dlx5/6, and reduced survival of cranial myogenic precursor cells.

Minimizing Biosignal Recording Sites for Noninvasive Hybrid Brain/Neural Control

Noninvasive brain/neural controlled robots are promising tools to improve autonomy and quality of life in severe paralysis, but require biosignal recordings, such as electroencephalography (EEG) and electrooculography (EOG), from various sites distributed over the user's head. This limits the applicability and practicality of noninvasive brain/neural robot control on an everyday basis. It would thus be very desirable to minimize the number of necessary recording sites paving the way for miniaturized, headset-like EEG/EOG systems that users with hemiplegia can mount by themselves. Here, we introduce a novel EEG/EOG brain/neural control strategy using only scalp electrodes placed near cortical sensorimotor areas. The strategy was tested across 16 healthy volunteers who engaged in an EEG/EOG brain/neural control task. Classification accuracies were compared using scalp electrodes only versus the conventional electrode placements across the scalp and face. To evaluate whether cranial muscle artifacts impede classification accuracy, participants were asked to clench their teeth during the task. We found that brain/neural classification accuracy was comparable and that clenching had no impact on classification accuracy across both conditions. Our results suggest that the proposed new strategy allows for reliable EEG/EOG-based brain/neural control, a critical prerequisite to broaden the use of noninvasive brain/neural assistive and rehabilitative technologies.

Pregabalin-induced neuroprotection and gait improvement in dystrophic MDX mice

Duchenne muscular dystrophy (DMD) is a genetic disease linked to the X chromosome induced by mutations in the dystrophin gene. Neuroprotective drugs, such as pregabalin (PGB), can improve motor function through the modulation of excitatory synapses, together with anti-apoptotic and anti-inflammatory effects. The present work studied the effects of PGB in the preservation of dystrophic peripheral nerves, allowing motor improvements in MDX mice. Five weeks old MDX and C57BL/10 mice were treated with PGB (30 mg/kg/day, i.p.) or vehicle, for 28 consecutive days. The mice were sacrificed on the 9th week, the sciatic nerves were dissected out and processed for immunohistochemistry and qRT-PCR, for evaluating the expression of proteins and gene transcripts related to neuronal activity and Schwann cell function. The lumbar spinal cords were also processed for qRT-PCR to evaluate the expression of neurotrophic factors and pro- and anti-inflammatory cytokines. Cranial tibial muscles were dissected out for endplate evaluation with α-bungarotoxin. The recovery of motor function was monitored throughout the treatment, using a spontaneous walking track test (Catwalk system) and a forced locomotion test (Rotarod). The results showed that treatment with PGB reduced the retrograde effects of muscle degeneration/regeneration on the nervous system from the 5th to the 9th week in MDX mice. Thus, PGB induced protein expression in neurons and Schwann cells, protecting myelinated fibers. In turn, better axonal morphology and close-to-normal motor endplates were observed. Indeed, such effects resulted in improved motor coordination of dystrophic animals. We believe that treatment with PGB improved the balance between excitatory and inhibitory inputs to spinal motoneurons, increasing motor control. In addition, PGB enhanced peripheral nerve homeostasis, by positively affecting Schwann cells. In general, the present results indicate that pregabalin is effective in protecting the PNS during the development of DMD, improving motor coordination, indicating possible translation to the clinic.

Anatomical features of the phytotelma dwelling, egg-eating, fanged tadpoles of Rhacophorus vampyrus (Anura: Rhacophoridae).

Tadpoles of the Vampire tree frog Rhacophorus vampyrus differ substantially from other rhacophorid tadpoles, by having profound modifications in external morphology. The morphological peculiarities of this species likely correlate with their arboreal microhabitat and strict oophagous diet. In this work, we examine buccal and musculoskeletal anatomy and compare them to other rhacophorid and egg-eating larvae. The shape and arrangement of cartilages of the lower jaw are unique among tadpoles, and the lack of a palatoquadrate suspensorium is only known in the distantly related macrophagous tadpoles of the dicroglossid Occidozyga baluensis. The cranial musculature is massive, and the morphology of several mandibular, hyoid, and abdominal muscles could be related to the ingestion and transit of large eggs. In the buccal cavity, conspicuous aspects are the absence of ridges and papillae, and the development of a unique glandular zone in the buccal floor. Finally, observations of the skeletal support of keratinized mouthparts allow us to present a topography-based hypothesis of homology of the conspicuous fangs of these tadpoles.

Cranial Musculoskeletal Description of Black-Throated Finch (Aves: Passeriformes: Estrildidae) with DiceCT.

Synopsis Dietary requirements and acquisition strategies change throughout ontogeny across various clades of tetrapods, including birds. For example, birds hatch with combinations of various behavioral, physiological, and morphological factors that place them on an altricial–precocial spectrum. Passeriformes (=songbirds) in particular, a family constituting approximately more than half of known bird species, displays the most drastic difference between hatchling and adults in each of these aspects of their feeding biology. How the shift in dietary resource acquisition is managed during ontogeny alongside its relationship to the morphology of the feeding apparatus has been largely understudied within birds. Such efforts have been hampered partly due to the small size of many birds and the diminutive jaw musculature they employ. In this study, we used standard and diffusible iodine-based contrast-enhanced computed tomography in conjunction with digital dissection to quantify and describe the cranial musculature of the Black-throated Finch (Poephila cincta) at fledgling and adult stages. Our results reveal that in both the fledgling and the adult, cranial musculature shows clear and complex partitioning in the Musculus adductor mandibulae externus that is consistent with other families within Passeriformes. We quantified jaw-muscle sizes and found that the adult showed a decrease in muscle mass in comparison to the fledgling individual. We propose that this could be the result of low sample size or a physiological effect of parental care in Passeriformes. Our study shows that high-resolution visualization techniques are informative at revealing morphological discrepancies for studies that involve small specimens such as Passeriformes especially with careful specimen selection criteria.

3D models related to the publication: The morphology and evolution of chondrichthyan cranial muscles: a digital dissection of the elephantfish Callorhinchus milii and the catshark Scyliorhinus canicula

This contribution contains 3D models of the cranial skeleton and muscles in an elephantfish (Callorhinchus milii) and a catshark (Scyliorhinus canicula), based on synchrotron tomographic scans. These datasets were analyzed and described in Dearden et al. (2021) The morphology and evolution of chondrichthyan cranial muscles: a digital dissection of the elephantfish Callorhinchus milii and the catshark Scyliorhinus canicula. Journal of Anatomy.

The morphology and evolution of chondrichthyan cranial muscles: A digital dissection of the elephantfish Callorhinchus milii and the catshark Scyliorhinus canicula.

The anatomy of sharks, rays, and chimaeras (chondrichthyans) is crucial to understanding the evolution of the cranial system in vertebrates due to their position as the sister group to bony fishes (osteichthyans). Strikingly different arrangements of the head in the two constituent chondrichthyan groups-holocephalans and elasmobranchs-have played a pivotal role in the formation of evolutionary hypotheses targeting major cranial structures such as the jaws and pharynx. However, despite the advent of digital dissections as a means of easily visualizing and sharing the results of anatomical studies in three dimensions, information on the musculoskeletal systems of the chondrichthyan head remains largely limited to traditional accounts, many of which are at least a century old. Here, we use synchrotron tomographic data to carry out a digital dissection of a holocephalan and an elasmobranch widely used as model species: the elephantfish, Callorhinchus milii, and the small-spotted catshark, Scyliorhinus canicula. We describe and figure the skeletal anatomy of the head, labial, mandibular, hyoid, and branchial cartilages in both taxa as well as the muscles of the head and pharynx. In Callorhinchus, we make several new observations regarding the branchial musculature, revealing several previously unreported or ambiguously characterized muscles, likely homologous to their counterparts in the elasmobranch pharynx. We also identify a previously unreported structure linking the pharyngohyal of Callorhinchus to the neurocranium. Finally, we review what is known about the evolution of chondrichthyan cranial muscles from their fossil record and discuss the implications for muscle homology and evolution, broadly concluding that the holocephalan pharynx is likely derived from a more elasmobranch-like form which is plesiomorphic for the chondrichthyan crown group. This dataset has great potential as a resource, particularly for researchers using these model species for zoological research, functional morphologists requiring models of musculature and skeletons, as well as for palaeontologists seeking comparative models for extinct taxa.

Combined Use of Chitosan and Olfactory Mucosa Mesenchymal Stem/Stromal Cells to Promote Peripheral Nerve Regeneration In Vivo

Peripheral nerve injury remains a clinical challenge with severe physiological and functional consequences. Despite the existence of multiple possible therapeutic approaches, until now, there is no consensus regarding the advantages of each option or the best methodology in promoting nerve regeneration. Regenerative medicine is a promise to overcome this medical limitation, and in this work, chitosan nerve guide conduits and olfactory mucosa mesenchymal stem/stromal cells were applied in different therapeutic combinations to promote regeneration in sciatic nerves after neurotmesis injury. Over 20 weeks, the intervened animals were subjected to a regular functional assessment (determination of motor performance, nociception, and sciatic indexes), and after this period, they were evaluated kinematically and the sciatic nerves and cranial tibial muscles were evaluated stereologically and histomorphometrically, respectively. The results obtained allowed confirming the beneficial effects of using these therapeutic approaches. The use of chitosan NGCs and cells resulted in better motor performance, better sciatic indexes, and lower gait dysfunction after 20 weeks. The use of only NGGs demonstrated better nociceptive recoveries. The stereological evaluation of the sciatic nerve revealed identical values in the different parameters for all therapeutic groups. In the muscle histomorphometric evaluation, the groups treated with NGCs and cells showed results close to those of the group that received traditional sutures, the one with the best final values. The therapeutic combinations studied show promising outcomes and should be the target of new future works to overcome some irregularities found in the results and establish the combination of nerve guidance conduits and olfactory mucosa mesenchymal stem/stromal cells as viable options in the treatment of peripheral nerves after injury.

Organization of the cephalic lateral-line canals in Electrophorus varii de Santana, Wosiacki, Crampton, Sabaj, Dillman, Mendes-Júnior & Castro e Castro, 2019 (Gymnotiformes: Gymnotidae)

Abstract Electrophorus spp. generate high-voltage electric discharges for defense and hunting, and low-voltage electric discharges (as other Gymnotiformes) for electrolocation and communication. Despite intense interest in the unusual electrogenic and electroreceptive capacities of electric eels, the other sensory systems of Electrophorus spp. are relatively poorly known. Here we describe the ontogenetic development and organization of the cephalic lateral-line canals in the lowland electric eel, Electrophorus varii. Preserved specimens of larvae, juveniles, and adults were examined to describe the spatial distribution of the canals and pores. Ontogenetic shifts of the cephalic lateral line formation were observed for each canal and support a hypothesis of non-synchronized development. The morphogenesis of cephalic canals in larvae and juveniles begins just before the onset of exogenous feeding. In adults, the cephalic sensory canals are formed separately from the skull and overlay cranial and mandibular bones and muscles. This study provides the first detailed description of the development and organization of the cephalic lateral-line system in Electrophorus varii.