Joy S. Reidenberg

The new face of gross anatomy.

The nature of anatomy education has changed substantially over the past decade due to both a new generation of students who learn differently from those of past years and the enormity of advances in anatomical imaging and viewing. At Mount Sinai School of Medicine, our anatomy courses have been designed to meld classic dissection with the tools physicians and surgeons will use tomorrow. We introduce students to the newest technologies available for viewing the body, such as minimally invasive approaches, ultrasonography, three‐dimensional visualizations, multi‐axial computerized image reconstructions, multi‐planar magnetic resonance imaging, and plastinated prosections. Students are given a hands‐on, team‐building experience operating laparoscopes in the laboratory. A great strength of our program is the important and active participation by faculty from 15 different basic and clinical departments, including several chairs and voluntary faculty. This interdisciplinary approach brings to our students direct, one‐on‐one encounters or presentations by our finest physicians and surgeons and our core anatomy faculty. In addition, the presence of many teaching assistants drawn from upper classmen and advanced graduate students adds an additional, vibrant dimension. Our anatomy programs for medical/graduate students and postgraduates are structured around three simple principles: (1) it is a privilege to teach, (2) we enlist only passionate teachers, and (3) it is our role to instill appreciation and respect for human form. Anat Rec (New Anat) 269:81–88, 2002.

The anatomy, physiology, acoustics and perception of speech: essential elements in analysis of the evolution of human speech

Abstract Inferences on the evolution of human speech based on anatomical data must take into account its physiology, acoustics and perception. Human speech is generated by the supralaryngeal vocal tract (SVT) acting as an acoustic filter on noise sources generated by turbulent airflow and quasi-periodic phonation generated by the activity of the larynx. The formant frequencies, which are major determinants of phonetic quality, are the frequencies at which relative energy maxima will pass through the SVT filter. Neither the articulatory gestures of the tongue nor their acoustic consequences can be fractionated into oral and pharyngeal cavity components. Moreover, the acoustic cues that specify individual consonants and vowels are “encoded”, i.e., melded together. Formant frequency encoding makes human speech a vehicle for rapid vocal communication. Non-human primates lack the anatomy that enables modern humans to produce sounds that enhance this process, as well as the neural mechanisms necessary for the voluntary control of speech articulation. The specific claims of Duchin (1990) are discussed.

Specializations of the human upper respiratory and upper digestive systems as seen through comparative and developmental anatomy

The human upper respiratory, or aerodigestive, tract serves as the crossroads of our breathing, swallowing and vocalizing pathways. Accordingly, developmental or evolutionary change in any of these functions will, of necessity, affect the others. Our studies have shown that the position in the neck of the mammalian larynx is a major factor in determining function in this region. Most mammals, such as our closest relatives the nonhuman primates, exhibit a larynx positioned high in the neck. This permits an intranarial larynx to be present and creates largely separate respiratory and digestive routes. While infant humans retain this basic mammalian pattern, developmental descent of the larynx considerably alters this configuration. Adult humans have, accordingly, lost separation of the respiratory and digestive routes, but have gained an increased supralaryngeal region of the pharynx which allows for the production of the varied sounds of human speech. How this region has changed during human evolution has been difficult to assess due to the absence of preserved soft-tissue structures. Our studies have shown that the relationship between basicranial shape and laryngeal position in living mammals can be a valuable guide to reconstruct the region in ancestral humans. Based on these findings we have examined the basicrania of fossil ancestors—from over two million years ago to near recent times—and have reconstructed the position of the larynx and pharyngeal region in these early forms. This has allowed us insight into how our ancestors may have breathed and swallowed, and when the anatomy necessary for human speech evolved.

Advances in understanding the relationship between the skull base and larynx with comments on the origins of speech

The position of upper respiratory structures, such as the larynx, has proven to be of great importance in determining an animal’s breathing, swallowing and vocalizing abilities. Studies on living mammals have also shown that the shape of the basicranium is related to the position of the larynx. This information has been of value in using the skull base as a means to reconstruct the upper respiratory tract of fossil hominids. Ongoing comparative and experimental studies of this region are adding new information on the mechanical relationship of the skull base to contiguous areas of the respiratory tract. For example, examination of the region in mammals disparate from humans, such as cetaceans, and experimental work on the region in rats, is adding new data on how the larynx and skull base may functionally interact.

Anatomical Adaptations of Aquatic Mammals

This special issue of the Anatomical Record explores many of the anatomical adaptations exhibited by aquatic mammals that enable life in the water. Anatomical observations on a range of fossil and living marine and freshwater mammals are presented, including sirenians (manatees and dugongs), cetaceans (both baleen whales and toothed whales, including dolphins and porpoises), pinnipeds (seals, sea lions, and walruses), the sea otter, and the pygmy hippopotamus. A range of anatomical systems are covered in this issue, including the external form (integument, tail shape), nervous system (eye, ear, brain), musculoskeletal systems (cranium, mandible, hyoid, vertebral column, flipper/forelimb), digestive tract (teeth/tusks/baleen, tongue, stomach), and respiratory tract (larynx). Emphasis is placed on exploring anatomical function in the context of aquatic life. The following topics are addressed: evolution, sound production, sound reception, feeding, locomotion, buoyancy control, thermoregulation, cognition, and behavior. A variety of approaches and techniques are used to examine and characterize these adaptations, ranging from dissection, to histology, to electron microscopy, to two‐dimensional (2D) and 3D computerized tomography, to experimental field tests of function. The articles in this issue are a blend of literature review and new, hypothesis‐driven anatomical research, which highlight the special nature of anatomical form and function in aquatic mammals that enables their exquisite adaptation for life in such a challenging environment. Anat Rec, 290:507–513, 2007.

Breaking symmetry: The marine environment, prey size, and the evolution of asymmetry in cetacean skulls

Skulls of odontocetes (toothed whales, including dolphins and porpoises) are typified by directional asymmetry, particularly in elements associated with the airway. Generally, it is assumed this asymmetry is related to biosonar production. However, skull asymmetry may actually be a by‐product of selection pressure for an asymmetrically positioned larynx. The odontocete larynx traverses the pharynx and is held permanently in place by a ring of muscle. This allows prey swallowing while remaining underwater without risking water entering the lungs and causing injury or death. However, protrusion of the larynx through the pharynx causes a restriction around which prey must pass to reach the stomach. The larynx and associated hyoid apparatus has, therefore, been shifted to the left to provide a larger right piriform sinus (lateral pharyngeal food channel) for swallowing larger prey items. This asymmetry is reflected in the skull, particularly the dorsal openings of the nares. It is hypothesized that there is a relationship between prey size and skull asymmetry. This relationship was examined in 13 species of odontocete cetaceans from the northeast Atlantic, including four narrow‐gaped genera (Mesoplodon, Ziphius, Hyperoodon, and Kogia) and eight wide‐gaped genera (Phocoena, Delphinus, Stenella, Lagenorhynchus, Tursiops, Grampus, Globicephala, and Orcinus). Skulls were examined from 183 specimens to assess asymmetry of the anterior choanae. Stomach contents were examined from 294 specimens to assess prey size. Results show there is a significant positive relationship between maximum relative prey size consumed and average asymmetry relative to skull size in odontocete species (wide‐gape species: R2 = 0.642, P = 0.006; narrow‐gape species: R2 = 0.909, P = 0.031). This finding provides support for the hypothesis that the directional asymmetry found in odontocete skulls is related to an aquatic adaptation enabling swallowing large, whole prey while maintaining respiratory tract protection. Anat Rec, 290:539–545, 2007.

Acoustic Models of Sound Production and Propagation

Acoustic models based on physics and mathematics may yield significant advances in the understanding of sound production, propagation, and interaction associated with whales and dolphins. Models can be used to estimate the limits of intensity and frequency that are physically possible given the anatomy of a species. Models can also tell us what kind of anatomical structures would be necessary in order to produce sound having specific characteristics. Models can be used to clarify what type of measurements should be performed to answer specific questions. Many areas of bioacoustics stand to benefit from simulation of sound propagation through biological tissues and the media surrounding them. However, accurate modeling of biological subjects with complex anatomical features is extremely challenging, and few modern studies exist of sound production and propagation in whales and dolphins.

Discovery of a low frequency sound source in Mysticeti (baleen whales): anatomical establishment of a vocal fold homolog.

The mechanism of mysticete (baleen whale) vocalization has remained a mystery. Vocal folds (true vocal “cords”), the structures responsible for sound production in terrestrial mammals, were thought to be absent in whales. This study tests the hypothesis that the mysticete larynx possesses structures homologous to vocal folds and that they are capable of sound generation. Laryngeal anatomy was examined in 37 specimens representing 6 mysticete species. Results indicate the presence of a U‐shaped fold (U‐fold) in the lumen of the larynx. The U‐fold is supported by arytenoid cartilages, controlled by skeletal muscles innervated by the recurrent laryngeal nerve, is adjacent to a diverticulum (laryngeal sac) covered with mucosa innervated by the superior laryngeal nerve, and contains a ligament—conditions that also define the vocal folds of terrestrial mammals and, therefore, supports homology. Unlike the vocal folds of terrestrial mammals, which are perpendicular to airflow, the mysticete U‐fold is oriented parallel to airflow. U‐fold adduction/abduction and elevation/depression may control airflow, and vibration of its edges may generate sounds. The walls of the laryngeal sac can expand and contract, may serve as a resonant space, and may also propagate vibrations generated by movements of the supporting arytenoid cartilages. The extensive musculature surrounding the laryngeal sac may enable rapid and forceful expulsion of air from the lumen of the sac into other respiratory spaces, or maintain a constant sac volume despite the effects of ambient pressure (e.g., changes during diving or ascent). The size and complexity of the mysticete larynx indicates an organ with multiple functions, including protection during breathing/swallowing, regulation of airflow and pressures in the respiratory spaces, and sound generation. The presence of a vocal fold homolog offers a new insight into both the mechanism of sound generation by mysticetes and the divergent evolution of odontocete and mysticete cetaceans. Anat Rec, 290:745–759, 2007.

Sisters of the Sinuses: Cetacean Air Sacs

This overview assesses some distinguishing features of the cetacean (whale, dolphin, porpoise) air sac system that may relate to the anatomy and function of the paranasal sinuses in terrestrial mammals. The cetacean respiratory tract has been modified through evolution to accommodate living in water. Lack of paranasal sinuses in modern cetaceans may be a diving adaptation. Bone‐enclosed air chambers are detrimental, as their rigid walls may fracture during descent/ascent due to contracting/re‐expanding air volumes. Flexible‐walled “sinuses” (extracranial diverticula) are a logical adaptation to diving. Odontocetes (toothed whales) exhibit several pairs of paranasal air sacs. Although fossil evidence indicates that paranasal sinuses occur in archaeocetes (ancestors/relatives of living cetaceans), it is not known whether the paranasal sacs derive from these sinuses. Sac pigmentation indicates that they derived from invaginations of the integument. Unlike sinuses, paranasal sacs are not circumferentially enclosed in bone, and therefore can accommodate air volume changes that accompany diving pressure changes. Paired pterygoid sacs, located ventrally along the cetacean skull, connect the pharynx and middle ear cavities. Mysticetes (baleen whales) have a large midline laryngeal sac. Although cetacean air sacs do not appear to be homologous to paranasal sinuses, they may serve some analogous respiratory, vocal, or structural functions. For example, these sacs may participate in gas exchange, thermoregulation, resonance, and skeletal pneumatization. In addition, they may subserve unique aquatic functions, such as increasing inspiratory volume, mitigating pressure‐induced volume change, air shunting to reduce respiratory dead space, and facilitating underwater sound production and transmission. Anat Rec, 291:1389–1396, 2008.

Evolution of hyperphalangy and digit reduction in the cetacean manus

Cetaceans (whales, dolphins, and porpoises) have a soft tissue flipper that encases most of the forelimb, and elongated digits with an increased number of phalanges (hyperphalangy). In addition, some cetaceans exhibit a reduction in digit number. Although toothed cetaceans (odontocetes) are pentadactylous, most baleen whales (mysticetes) are tetradactylous and also lack a metacarpal. This study conducts a survey of cetacean metacarpal and phalangeal morphologies, traces the evolution of hyperphalangy in a phylogenetic context, optimizes characters onto previously published cetacean phylogenies, and tests various digit loss hypotheses. Dissections were performed on 16 cetacean flippers representing 10 species (8 mysticetes, 2 odontocetes). Phalangeal count data were derived from forelimb radiographs (36 odontocetes, 5 mysticetes), osteological specimens of articulated forelimbs (8 mysticetes), and were supplemented with published counts. Modal phalangeal counts were coded as ordered and unpolarized characters and optimized onto two known cetacean phylogenies. Results indicate that digital ray I is reduced in many cetaceans (except Globicephala) and all elements of digital ray I were lost in tetradactylous mysticetes. Fossil evidence indicates this ray may have been lost approximately 14 Ma. Most odontocetes also reduce the number of phalangeal elements in digit V, while mysticetes typically retain the plesiomorphic condition of three phalanges. Results from modal phalangeal counts show the greatest degree of hyperphalangy in digits II and III in odontocetes and digits III and IV in mysticetes. Fossil evidence indicates cetacean hyperphalangy evolved by at least 7–8 Ma. Digit loss and digit positioning may underlie disparate flipper shapes, with narrow, elongate flippers facilitating fast swimming and broad flippers aiding slow turns. Hyperphalangy may help distribute leading edge forces, and multiple interphalangeal joints may smooth leading edge flipper contour. Anat Rec, 290:654–672, 2007.