A morphometric comparison of the ductus reuniens in humans and guinea pigs, with a note on its evolutionary importance.

The mammalian inner ear contains the sensory organs responsible for balance (semicircular canals, utricle, and saccule) and hearing (cochlea). While these organs are functionally distinct, there exists a critical structural connection between the two: the ductus reuniens (DR). Despite its functional importance, comparative descriptions of DR morphology are limited, hindering our understanding of the evolutionary diversification of hearing and balance systems among mammals. Using virtual 3D models derived from micro-CT, we examine the morphology of the DR and its relationship to the bony labyrinth in humans compared to that in a commonly used animal model, the guinea pig. Anatomical reconstructions and univariate measurements were carried out in the software 3D Slicer. Data indicate similarities in DR morphology between humans and guinea pigs in terms of overall shape. However, there are considerable differences in relative DR length and width between humans and guinea pigs. Humans possess a relatively shorter and narrower DR but with wider openings to the saccule and cochlear duct. This results in a relatively more constricted DR lumen in humans which may differentially limit fluid transfer between the saccule and cochlea. Our results reveal previously hidden morphological diversity in the communication between the hearing and balance systems of the mammalian inner ear which may indicate alternative strategies for isolating the Organ of Corti from the peripheral vestibular system throughout mammalian evolution.

Human dissection for anesthesiology resident training augments anatomical knowledge and clinical skills.

Anatomy is an essential component of clinical anesthesiology. The use of simulated patients and alternative materials, including embalmed human bodies, have become increasingly common during resident physician training due to the deemphasis on anatomical education during undergraduate medical training. In this report, the need for a more extensive review of relevant anatomy for the practice of anesthesiology was addressed by the design, evaluation, and dissemination of a human dissection course for procedural training of anesthesiology residents. The course utilized "freedom art" embalmed human bodies that allowed trainees to perform ultrasound-based regional and neuraxial techniques followed by detailed dissections of critical anatomy. One hundred and four residents participated in workshops and small group discussions and were evaluated using pre- and post-course assessments. A variety of clinical techniques were performed on the bodies, including regional blocks and neuraxial catheter placement. Insertion of peripheral/neuraxial catheters was successful, with dissections demonstrating the expected placement. Assessment scores improved following the course (pre-course mean 52.7%, standard deviation (σ) 13.1%; post-course mean 72.2%, σ 11.6%; t-test p < 0.0001) and feedback highlighted the usefulness and clinical relevance of course content. The ability to correlate ultrasound imaging with subsequent dissections of the "blocked" area and visualization of dye staining was extremely relevant for spatial understanding of the anatomy relevant for the clinical practice of these techniques. This manuscript demonstrates successful implementation of a comprehensive course for anesthesiology resident physicians to address gaps in undergraduate anatomical education and suggests that broader adoption of dissection courses may be beneficial for training anesthesiologists.

Understanding the intentional acoustic behavior of humpback whales: a production-based approach.

Following a production-based approach, this paper deals with the acoustic behavior of humpback whales. This approach investigates various physical factors, which are either internal (e.g., physiological mechanisms) or external (e.g., environmental constraints) to the respiratory tractus of the whale, for their implications in sound production. This paper aims to describe a functional scenario of this tractus for the generation of vocal sounds. To do so, a division of this tractus into three different configurations is proposed, based on the air recirculation process which determines air sources and laryngeal valves. Then, assuming a vocal function (in sound generation or modification) for several specific anatomical components, an acoustic characterization of each of these configurations is proposed to link different spectral features, namely, fundamental frequencies and formant structures, to specific vocal production mechanisms. A discussion around the question of whether the whale is able to fully exploit the acoustic potential of its respiratory tractus is eventually provided.

First evidence of the link between internal and external structure of the human inner ear otolith system using 3D morphometric modeling.

Our sense of balance is among the most central of our sensory systems, particularly in the evolution of human positional behavior. The peripheral vestibular system (PVS) comprises the organs responsible for this sense; the semicircular canals (detecting angular acceleration) and otolith organs (utricle and saccule; detecting linear acceleration, vibration, and head tilt). Reconstructing vestibular evolution in the human lineage, however, is problematic. In contrast to considerable study of the canals, relationships between external bone and internal membranous otolith organs (otolith system) remain largely unexplored. This limits our understanding of vestibular functional morphology. This study combines spherical harmonic modeling and landmark-based shape analyses to model the configuration of the human otolith system. Our approach serves two aims: (1) test the hypothesis that bony form covaries with internal membranous anatomy; and (2) create a 3D morphometric model visualizing bony and membranous structure. Results demonstrate significant associations between bony and membranous tissues of the otolith system. These data provide the first evidence that external structure of the human otolith system is directly related to internal anatomy, suggesting a basic biological relationship. Our results visualize this structural relationship, offering new avenues into vestibular biomechanical modeling and assessing the evolution of the human balance system.

Essential anatomy for core clerkships: A clinical perspective.

Clerkships are defining experiences for medical students in which students integrate basic science knowledge with clinical information as they gain experience in diagnosing and treating patients in a variety of clinical settings. Among the basic sciences, there is broad agreement that anatomy is foundational for medical practice. Unfortunately, there are longstanding concerns that student knowledge of anatomy is below the expectations of clerkship directors and clinical faculty. Most allopathic medical schools require eight "core" clerkships: internal medicine (IM), pediatrics (PD), general surgery (GS), obstetrics and gynecology (OB), psychiatry (PS), family medicine (FM), neurology (NU), and emergency medicine (EM). A targeted needs assessment was conducted to determine the anatomy considered important for each core clerkship based on the perspective of clinicians teaching in those clerkships. A total of 525 clinical faculty were surveyed at 24 United States allopathic medical schools. Participants rated 97 anatomical structure groups across all body regions on a 1-4 Likert-type scale (1 = not important, 4 = essential). Non-parametric ANOVAs determined if differences existed between clerkships. Combining all responses, 91% of anatomical structure groups were classified as essential or more important. Clinicians in FM, EM, and GS rated anatomical structures in most body regions significantly higher than at least one other clerkship (p = 0.006). This study provides an evidence-base of anatomy content that should be considered important for each core clerkship and may assist in the development and/or revision of preclinical curricula to support the clinical training of medical students.

Nasopharyngeal morphology contributes to understanding the "muddle in the middle" of the Pleistocene hominin fossil record.

The late archeologist Glynn Isaac first applied the term "muddle in the middle" to a poorly understood period in the Middle Pleistocene human fossil record. This study uses the nasopharyngeal boundaries as a source of traits that may inform this unclear period of human evolution. The nasopharynx lies at the nexus of several vital physiological systems, yet relatively little is known about its importance in human evolution. We analyzed a geographically diverse contemporary Homo sapiens growth series (n = 180 adults, 237 nonadults), Homo neanderthalensis (La Chapelle aux Saints 1, La Ferrassie 1, Forbes Quarry 1, Monte Circeo 1, and Saccopastore 1), mid-Pleistocene Homo (Atapuerca 5, Kabwe 1, Petralona 1, and Steinheim 1), and two Homo erectus sensu lato (KNM-ER 3733 and Sangiran 17). Methods include traditional (Analysis 1) and 3D geometric morphometric analysis (Analysis 2). H. erectus exhibited tall, narrow nasopharyngeal shape, a robust, ancestral morphology. Kabwe 1 and Petralona 1 plotted among H. sapiens in Analysis 2, exhibiting relatively shorter and vertical cartilaginous Eustachian tubes and vertical medial pterygoid plates. Atapuerca 5 and Steinheim 1 exhibited horizontal vomeral orientation similar to H. neanderthalensis, indicating greater relative soft palate length and anteroposterior nasopharynx expansion. They may exhibit synapomorphies with H. neanderthalensis, supporting the accretionary hypothesis. Species-level differences were found among H. sapiens and H. neanderthalensis, including relatively longer dilator tubae muscles and extreme facial airorhynchy among Neanderthals. Furthermore, H. neanderthalensis were autapomorphic in exhibiting horizontal pterygoid plate orientation similar to human infants, suggesting that they may have had inferiorly low placement of the torus tubarius and Eustachian tube orifice on the lateral nasopharyngeal wall in life. This study supports use of osseous nasopharyngeal boundaries both for morphological characters and understanding evolution of otitis media susceptibility in living humans.

Three-dimensional visualization of the human membranous labyrinth: The membrana limitans and its role in vestibular form.

The inner ear contains the end organs for balance (vestibular labyrinth) and hearing (cochlea). The vestibular labyrinth is comprised of the semicircular canals (detecting angular acceleration) and otolith organs (utricle and saccule, which detect linear acceleration and head tilt relative to gravity). Lying just inferior to the utricle is the membranous membrana limitans (ML). Acting as a keystone to vestibular geometry, the ML provides support for the utricular macula and acts as a structural boundary between the superior (pars superior) and inferior (pars inferior) portions of the vestibular labyrinth. Given its importance in vestibular form, understanding ML morphology is valuable in establishing the spatial organization of other vestibular structures, particularly the utricular macula. Knowledge of the 3D structure and variation of the ML, however, remain elusive. Our study addresses this knowledge gap by visualizing, in 3D, the ML and surrounding structures using micro-CT data. By doing so, we attempt to clarify: (a) the variation of ML shape; (b) the reliability of ML attachment sites; and (c) the spatial relationship of the ML to the stapes footplate using landmark-based Generalized Procrustes, Principal Component and covariance analyses. Results indicate a consistent configuration of three distinct bony ML attachments including an anterolateral, medial, and posterior attachment which all covary with bony structure. Our results set the stage for further understanding into vestibular and more specifically, utricular macula spatial configuration within the human head, offering the potential to aid in clinical and evolutionary studies which rely on a 3D understanding of vestibular spatial configuration.

Insights into Inner Ear Function and Disease Through Novel Visualization of the Ductus Reuniens, a Seminal Communication Between Hearing and Balance Mechanisms.

The sensory end-organs responsible for hearing and balance in the mammalian inner ear are connected via a small membranous duct known as the ductus reuniens (also known as the reuniting duct (DR)). The DR serves as a vital nexus linking the hearing and balance systems by providing the only endolymphatic connection between the cochlea and vestibular labyrinth. Recent studies have hypothesized new roles of the DR in inner ear function and disease, but a lack of knowledge regarding its 3D morphology and spatial configuration precludes testing of such hypotheses. We reconstructed the 3D morphology of the DR and surrounding anatomy using osmium tetroxide micro-computed tomography and digital visualizations of three human inner ear specimens. This provides a detailed, quantitative description of the DR's morphology, spatial relationships to surrounding structures, and an estimation of its orientation relative to head position. Univariate measurements of the DR, inner ear, and cranial planes were taken using the software packages 3D Slicer and Zbrush. The DR forms a narrow, curved, flattened tube varying in lumen size, shape, and wall thickness, with its middle third being the narrowest. The DR runs in a shallow bony sulcus superior to the osseus spiral lamina and adjacent to a ridge of bone that we term the "crista reuniens" oriented posteromedially within the cranium. The DR's morphology and structural configuration relative to surrounding anatomy has important implications for understanding aspects of inner ear function and disease, particularly after surgical alteration of the labyrinth and potential causative factors for Ménière's disease.

Racism, structural racism, and the American Association for Anatomy: Initial report from a task force.

In 2021, the American Association for Anatomy (AAA) Board of Directors appointed a Task Force on Structural Racism to understand how the laws, rules, and practices in which the Association formed, developed and continues to exist affect membership and participation. This commentary is the first public report from the Task Force. We focus on African Americans with some comments on Jews and women, noting that all marginalized groups deserve study. Through much of its 130 year history, some members were an essential part of perpetuating racist ideas, the Association largely ignored racism and had some practices that prevented participation. The Task Force concluded that individual and structural racism within the AAA, combined with the broader social context in which the Association developed, contributed to the current underrepresentation of African Americans who constitute 4.1% of the membership even though 13.4% of the U.S. population is Black. Intentional efforts within the AAA to reckon with racism and other forms of bias have only begun in the last 10-20 years. These actions have led to more diverse leadership within the Association, and it is hoped that these changes will positively affect the recruitment and retention of marginalized people to science in general and anatomy in particular. The Task Force recommends that the AAA Board issue a statement of responsibility to acknowledge its history. Furthermore, the Task Force advocates that the Board commit to (a) sustaining ongoing projects to improve diversity, equity, and inclusion and (b) dedicating additional resources to facilitate novel initiatives.

The building bridges initiative in health sciences and medical education: Fostering connections between Brazil and the United States.

Building Bridges is an outreach initiative that has focused upon effectuating increased communication among biomedical scientists, educators, and students in Brazil and the United States-the countries with the greatest number of medical schools in the Americas. It has been a developing project over the last 6 years, and has involved faculty, students, and civic leaders from many universities in the two countries. This Special Issue of The Anatomical Record is a continuation of the Building Bridges initiative, and brings to the fore attention onto some of the creative research being done in biomedical science, evolutionary science, biomedical education, and current health topics in Brazil. Fostering open routes of communication among scientists is a core humanistic value that is at the heart of progress and is the center of our actions. This paper reviews the history of the Building Bridges Initiative.

Alterations to vestibular morphology in highly bred domestic dogs may affect balance.

The modern domestic dog (Canis lupus familiaris) provides an excellent model to examine the effects of cranial modification. Extreme variation in skull length among dog breeds due to high levels of selective breeding is known to be linked to disorders of the head and neck. Such alteration may also influence sensory organs including those of the vestibular system (VS), one of the most fundamental sense organs, essential in maintaining balance. Studies in mammals have shown that orientation of ipsilateral semicircular canals (SCCs) of the VS at right angles (orthogonality) is related to angular acceleration sensitivity. Due to their considerable variation in craniofacial form while exhibiting similar locomotion, domestic dogs provide an excellent natural experiment to examine if cranial alteration influences VS functional morphology. Our methods examine how change in cranial base length across dog breeds relates to SCC orthogonality using linear modeling and analyses of variance. The sample studied (29 bony labyrinths of 17 dog breeds) was obtained from a previous study on canid inner ear metrics. Results support the hypothesis that orthogonality between the anterior and posterior SCC + ampulla significantly correlates with cranial base length. This suggests a close relationship between the orientations of SCCs with their ampullae and cranial structure among dog breeds. Specifically, highly derived breeds, such as the brachycephalic pug, have anterior and posterior SCCs and ampullae that deviate the most from orthogonality. Therefore, such highly bred domestic dogs may also have altered vestibular function due to compressed cranial form.

Identification of critical windows in early development of human upper respiratory tract and middle ear disease.

Otitis media (OM) or middle ear disease is a prevalent pediatric condition generally related to early growth of the cartilaginous Eustachian tube (CET). This study used a developmental series of dry crania to reconstruct CET and dilator tubae (DT, the muscle opening the CET) morphology. Timing and directionality of CET and upper respiratory tract (URT) growth were investigated. Traditional and 3D geometric morphometrics (GM) were used to assess bony landmarks on the crania. The series was divided using dental eruption into seven growth stages ranging from before eruption of deciduous dentition (approximately the first 6 postnatal months) to eruption of the first permanent maxillary molar (after approximately 6 years). Bony endpoints of the CET and DT were used to calculate their morphology. GM analysis showed substantial shape differences between newborns, early infants, and all later developmental stages. Univariate measures showed the largest growth change between birth and 6 months. Subsequently, CET morphology changed little in the latter half of year 1, instead maturing gradually until approximately 3 years whereas DT relative length and orientation finish growth by the end of year 1. Incongruence in slower CET growth and faster DT growth could impact CET function between 6 and 12 months and be a contributing factor of OM. Tubal aeration may improve after this time when both CET and DT morphology mature, coinciding with clinically reported drop-off in ear infections.

The Anatomical Record continues to replace wonder with knowledge through first-hand experience of acupuncture.

A group of original papers is assembled for this thematic-papers issue on traditional Chinese medicine (TCM). The idea for a thematic-papers issue came from Associate Editor and Guest Editor, Jicheng Li. Jicheng's idea was to introduce concepts and studies of TCM to the editorial board of The Anatomical Record and the Journal's readership. Thus, nine papers are published that deal with biomarkers, animal models, or treatments of TCM syndromes. Uniquely, Jicheng's effort culminated in acupuncture treatment of the editorial board members by a licensed physician of TCM. We learned, first-hand by Dr. Weixue Wang, about this ancient and vibrant holistic philosophy and medical practice. Our pleasure is to share the topic and our experience with you.

Extreme Anatomy: The Lottery Winners, Specialists, and Extreme Adaptations That Are No More.

This special issue of The Anatomical Record explores extravagant adaptions that vertebrates have evolved from their base groups to survive in the most challenging environments. It stems from a symposium entitled "Extreme Anatomy: Living beyond the edge," which was held April 23, 2017, at the annual meeting of the American Association for Anatomy, in Chicago, IL. In Part 1 of this issue, we examined extreme morphologies that allow exploration of new niches. In this issue, we return to the evolution of terrestriality by digging deeply into the fossil history of the piscine antecedent of tetrapods. These were truly "lottery winners" among vertebrates. This issue also bears on extreme specialists that once thrived but are now long extinct and some extant species that thrive in the hottest terrestrial niches. Herein, several contributions discuss developmental strategies that facilitate later demanding locomotor regimens and feeding strategies for accessing nutrients from less than ideal food sources. From mole-rats to short-faced breeds of domestic dogs, we encounter another host of the most unusual of earth's creatures, who have much to teach us about our world. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:214-217, 2020. © 2019 American Association for Anatomy.

Extreme Anatomy: Gear for the Pioneer.

This special issue of The Anatomical Record explores extravagant adaptions that vertebrates have evolved from their base groups to survive in the most challenging environments. The special issue stems from a symposium entitled "Extreme Anatomy: Living beyond the edge," which was held April 23, 2017, at the annual meeting of the American Association of Anatomists, (now called the American Association for Anatomy), in Chicago, IL. In part 1 of this issue, we encounter fossorial mammals and cave-dwelling fish and salamanders that have reduced visual systems accompanied by a variety of mechanosensory adaptations. In rivers and seas, teeth may not suffice in the pursuit of prey: aquatic vertebrates are adorned with armor or weaponry or elaborate keratinous sieves. As vertebrates exploit a great diversity of niches, selection has favored a dizzying array of specialized sensory and locomotor adaptions for deep diving, rapid flight, and navigation through dark and complex settings. Each special adaptation, some seemingly quite "extreme" deviations from an original Bauplan, becomes a tool for a pioneer-like diversification of vertebrates. Anat Rec, 2019. © 2019 American Association for Anatomy.

Reconstructing the Neanderthal Eustachian Tube: New Insights on Disease Susceptibility, Fitness Cost, and Extinction.

Neanderthals are among the best studied and yet most enigmatic fossil human groups with aspects of their anatomy and functional morphology remaining poorly understood. We present the first anatomical reconstruction of the Neanderthal cartilaginous Eustachian tube (CET), a vital component of the upper respiratory tract and nexus for the middle ear and postnasal airway. The Eustachian (auditory, pharyngotympanic) tube, comprised of a bony and cartilaginous (CET) portion, is integral to normal physiological functions such as middle ear aeration and pressure equilibration. Findings indicate that Neanderthal tubal morphology may have predisposed them to high rates of middle ear disease (otitis media [OM]). In living humans, mechanical CET dysfunction underlies OM in infants and young children, with sequelae including hearing loss, meningitis, and pneumonia. Despite proven linkage of CET malfunction with OM, the role of CET morphology in Neanderthal health and disease remains unstudied. We reconstructed Neanderthal CET morphology, comparing their crania to a modern human growth series. Methods included geometric morphometrics and univariate measures among Procrustes-fitted coordinates. Results showed Neanderthal adults exhibiting primitively tall and narrow nasopharynges with infant-like horizontal CET and choanal orientation. As horizontal CET orientation is associated with increased OM incidence in infants and children until around age six, its appearance in Neanderthal adults strongly indicates persistence of high OM susceptibility at this time. This could have compromised fitness and disease load relative to sympatric modern humans, affecting Neanderthals' ability to compete within their ecological niche, and potentially contributing to their rapid extinction. Anat Rec, 302:2109-2125, 2019. © 2019 American Association for Anatomy.

The Nasal Complex of a Semiaquatic Artiodactyl, the Moose (Alces alces): Is it a Good Evolutionary Model for the Ancestors of Cetaceans?

Among Cetartiodactyla, cetaceans are the only obligate aquatic dwellers. Given morphological similarities between cetacean relatives such as Indohyus (the best represented Eocene raoellid artiodactyl) with other, later artiodactyls, any crown artiodactyl that engages in aquatic behaviors is of interest as an evolutionary model for the adaptations that accompanied the origins of cetaceans. The American moose (Alces alces) is the only non-cetacean artiodactyl to engage in aquatic foraging and, other than Hippopotamus, is distinctive in its diving behaviors. This study surveyed the soft and hard tissue nasal morphology of Alces alces to assess phylogenetic polarity and the presence of adaptations for diving and feeding in fresh water habitats. A fresh dissection of the facial musculature and nasal cavity was performed on one subadult male individual and osteological analyses were also performed on dry crania. This species was analyzed alongside fossil crania of Cervalces (its presumed ancestor), other cervids (e.g., Odocoileus virginianus, the white tail deer; Dama dama, the fallow deer), a bovid (Bos taurus, domestic cattle), and a carnivoran (Ursus americanus, the American black bear). A fresh dissection of the facial musculature and nasal anatomy of one fallow deer specimen was also performed for comparison with the moose. Results indicate that Alces alces exhibited a primitive configuration of maxillolabial muscles and, like Dama, exhibited a series of subcutaneous fibrous tissues connecting these muscles to skin. Alces and Dama, however, both exhibited autapomorphies in the soft tissue anatomy of the external nares. The former possessed a series of muscles that act to constrict the anterior nares, likely during diving. Extremely large fibrofatty pads that were perforated by muscle tendon supported their alar fold. Internally, a double-scrolled maxilloturbinal occupied nearly the entire volume of the anterior nasal cavity and protruded beyond the rim of the piriform aperture in dry crania. Dama had long, thin muscles taking origin on their nasal conchae and inserting onto the alar fold. Yet, despite these anterior nasal autapomorphies, the ethmoturbinal patterns of all observed cervids and the one bovid all appeared primitive with a posteroinferiorly oriented array of ethmoturbinals in close contact with a relatively straight cribriform plate, a macrosmatic condition. These differed from the curved cribriform plate of Ursus whose posterior nasal anatomy appeared hyper-macrosmatic. Indohyus exhibits no skeletal sign of a fleshy proboscis such as an enlarged piriform aperture or shortened nasal bones. Thus, there is little evidence that the early ancestors of cetaceans engaged in prolonged bouts of diving for aquatic foods but more probably were surface swimmers traveling between terrestrial food sources or fleeing predators. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:667-692, 2019. © 2018 Wiley Periodicals, Inc.