Laryngeal Sac Research Articles

Saccular Cyst of the Larynx - A Clinical Case

Saccular cyst of the larynx is a benign supraglottic lesion, filled with mucus. It forms from the laryngeal sac, which is a soft tissue mass that is an extension of the laryngeal ventricle. Due to the extreme rarity, the true prevalence of the disease is unknown, although congenital laryngeal cysts have been reported to affect 1 in 300,000 newborns. The gold standard for diagnosing of saccular laryngeal cysts is laryngoscopy. Treatment of saccular cysts can only be done surgically, using endoscopic or external access. It is believed that endoscopic CO2 laser excision is the treatment of choice.

Anatomical mechanism for protecting the airway in the largest animals on earth

Separation of respiratory and digestive tracts in the mammalian pharynx is critical for survival. Food must be kept out of the respiratory tract, and air must be directed into the respiratory tract when breathing.1 Cetaceans have the additional problem of feeding while underwater. Lunge-feeding baleen whales (rorquals) open the mouth while swimming at high speeds to engulf a volume of prey-laden water as large as their own body2 and experience tremendous forces as water floods the mouth. How the respiratory tract is protected in the pharynx during engulfment and while swallowing a massive slurry of tiny living prey remains unknown, despite its importance to survival. By dissecting adult and fetal fin whales, we determined that a large musculo-fatty structure passively seals the oropharyngeal channel. This "oral plug" is not observed in other animals, and its position indicates it must be shifted to allow swallowing; it is a part of the soft palate and can only shift posteriorly and dorsally. Elevation of the oral plug allows food transfer to the pharynx and protects the upper airways from food entry. The laryngeal inlet in the floor of the pharynx is sealed by laryngeal cartilages, and the muscular laryngeal sac moves upward into the laryngeal cavity, completely occluding the airway. The pharynx is dedicated to the digestive tract during swallowing, with no connection between upper and lower airways. These adaptations to facilitate swallowing were a critical development in the evolution of large body size in these, the largest animals on earth.

How do Mysticete (Baleen) Whales Make Two Sounds Simultaneously?

Mysticete (baleen) whales use the larynx to generate sounds. Air flowing past the U‐shaped vocal folds causes vibrations that are transferred through overlying throat tissues to water. Sounds can be made repetitively without surfacing for a breath due to air recycling between lungs and larynx. We hypothesize that tissue movements direct airflow between sound generating and air recycling regions of the larynx. Methods involved examination of twenty mysticete specimens found beached along the northeast US coastline. Larynges were recovered post mortem from carcasses of minke (Balaenoptera acutorostrata), fin (B. physalus), sei (B. borealis), blue (B. musculus), humpback (Megaptera novaeangliae), and right (Eubalaena glacialis) whales. All specimens were collected under the auspices of the Marine Mammal Health and Stranding Response Program, and possession was permitted via a letter of authorization from NOAA‐NMFS. Results show that the larynx has two valves. One valve is located between the vocal folds. This valve is aided by a newly discovered cushion of tissue on the ventral surface of the cricoid cartilage. It appears to function like a plug, apparently hermetically sealing the gap between the vocal folds. Air flowing around this interlock is channeled superiorly between the corniculate cartilages. A second valve is found between the paired corniculate cartilages. Closure is aided by raising the epiglottis to plug the gap between the corniculates. This seals the rostral larynx, preventing air from escaping towards the nose. Air is instead diverted ventrally between the vocal folds and into the laryngeal sac. These two valves direct airflow towards vocal folds or corniculate flaps. Flow between the vocal folds may generate song, and allow extended vocalizations as air is captured and recycled between the laryngeal sac and the lungs. Flow between the corniculate flaps may generate pulses, but these sounds would continue only until the nasal region becomes pressurized.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Anatomy and Functional Morphology of the Mysticete Rorqual Whale Larynx: Phonation Positions of the U-Fold.

Many Mysticetes (baleen whales) are acoustically active marine mammals. This is epitomized by rorquals, and specifically male humpback whales (Megaptera novaeangliae) whose complex songs comprise a wide range of vocalizations. The sound production mechanism of odontocetes (toothed whales, including dolphins and porpoises) is well described, in contrast to that of mysticetes whose vocalization mechanism remains a subject of active scientific investigation. Anatomical observations and acoustic signal processing have led to divergent hypotheses under the framework of a production-based approach. We attempt to unify these hypotheses by broadening existing data with our new anatomical investigation, interpreted in light of known acoustical properties of mysticete vocalizations. We examined 15 specimens of four rorqual species: sei whale (Baleanoptera borealis), fin whale (Baleanoptera physalus), minke whale (Baleanoptera acutorostrata), and humpback whale (Megaptera novaeangliae). Based on these data and on previous literature, we propose a description of three functional positions (rest, breathing, and recirculation), unidirectional egressive airflow for sound production (from lungs to laryngeal sac), and new nomenclature for different parts of the U-fold (distal section, midsection, and corniculate flaps). Each of these sections has specific morphological and acoustical properties that support the concept of "mode variation" in baleen whale vocalizations. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:703-717, 2019. © 2018 Wiley Periodicals, Inc.

A pulsed-air model of blue whale B call vocalizations

Blue whale sound production has been thought to occur by Helmholtz resonance via air flowing from the lungs into the upper respiratory spaces. This implies that the frequency of blue whale vocalizations might be directly proportional to the size of their sound-producing organs. Here we present a sound production mechanism where the fundamental and overtone frequencies of blue whale B calls can be well modeled using a series of short-duration (<1 s) wavelets. We propose that the likely source of these wavelets are pneumatic pulses caused by opening and closing of respiratory valves during air recirculation between the lungs and laryngeal sac. This vocal production model is similar to those proposed for humpback whales, where valve open/closure and vocal fold oscillation is passively driven by airflow between the lungs and upper respiratory spaces, and implies call frequencies could be actively changed by the animal to center fundamental tones at different frequency bands during the call series.

Congenital laryngeal saccular cyst: a case report and literature review

Introducción. El quiste sacular congénito es una lesión rara, pero benigna, dada por la dilatación del sáculo laríngeo que se llena de moco y que no se comunica con el lumen laríngeo. Según la literatura, su tratamiento definitivo es quirúrgico. Objetivo. Realizar una revisión de la literatura y el reporte de un caso de quiste sacular laríngeo congénito y su tratamiento mediante abordaje endoscópico y uso de radiofrecuencia.Materiales y métodos. Se realizó la presentación del caso clínico y se llevó a cabo una revisión de la literatura en las bases de datos de Pubmed y Tripdatabase usando palabras claves descritas.Resultados. Esta patología es escasa, con una incidencia de 1.82 casos por 100 000 nacidos vivos. El diagnostico se realiza por medio de endoscopia laríngea, imágenes o revisión de la clínica. El caso expuesto es de una paciente recién nacida que presenta estridor y dificultad respiratoria y es diagnosticada con quiste sacular laríngeo, el cual es resecado de forma quirúrgica por medio de endoscopia con uso de radiofrecuencia. El procedimiento da como resultado la no reaparición del quiste.Conclusiones. Pese a no existir muchos reportes de caso, hay que conocer las características del quiste sacular congénito para poder realizar el tratamiento adecuado con los recursos disponibles. Es posible realizar resección endoscópica de esta lesión si es &lt;3cm por medio de radiofrecuencia, un método seguro y eficaz.

Two new theoretical roles of the laryngeal sac of humpback whales

Marine Mammal ScienceVolume 31, Issue 2 p. 774-781 Notes Two new theoretical roles of the laryngeal sac of humpback whales Nadège Gandilhon, Nadège Gandilhon UMR BOREA, Biologie des Organismes et Écosystèmes Aquatiques, équipe DYNECAR, Université UPMC, Université des Antilles et de la Guyane, FranceSearch for more papers by this authorOlivier Adam, Corresponding Author Olivier Adam Centre de Neurosciences Paris Sud, Bioacoustics Team, CNRS UMR 8195, Université Paris Sud Orsay, Orsay, France Institut d'Alembert, équipe Lutheries Acoustique Musicale (LAM), CNRS UMR 7190, Université UPMC, Paris, FranceCorresponding author (e-mail: [email protected]).Search for more papers by this authorDorian Cazau, Dorian Cazau Institut d'Alembert, équipe Lutheries Acoustique Musicale (LAM), CNRS UMR 7190, Université UPMC, Paris, FranceSearch for more papers by this authorJeffery T. Laitman, Jeffery T. Laitman Center for Anatomy and Functional Morphology, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York 10029-6574, U.S.ASearch for more papers by this authorJoy S. Reidenberg, Joy S. Reidenberg Center for Anatomy and Functional Morphology, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York 10029-6574, U.S.ASearch for more papers by this author Nadège Gandilhon, Nadège Gandilhon UMR BOREA, Biologie des Organismes et Écosystèmes Aquatiques, équipe DYNECAR, Université UPMC, Université des Antilles et de la Guyane, FranceSearch for more papers by this authorOlivier Adam, Corresponding Author Olivier Adam Centre de Neurosciences Paris Sud, Bioacoustics Team, CNRS UMR 8195, Université Paris Sud Orsay, Orsay, France Institut d'Alembert, équipe Lutheries Acoustique Musicale (LAM), CNRS UMR 7190, Université UPMC, Paris, FranceCorresponding author (e-mail: [email protected]).Search for more papers by this authorDorian Cazau, Dorian Cazau Institut d'Alembert, équipe Lutheries Acoustique Musicale (LAM), CNRS UMR 7190, Université UPMC, Paris, FranceSearch for more papers by this authorJeffery T. Laitman, Jeffery T. Laitman Center for Anatomy and Functional Morphology, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York 10029-6574, U.S.ASearch for more papers by this authorJoy S. Reidenberg, Joy S. Reidenberg Center for Anatomy and Functional Morphology, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York 10029-6574, U.S.ASearch for more papers by this author First published: 01 December 2014 https://doi.org/10.1111/mms.12187Citations: 8Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume31, Issue2April 2015Pages 774-781 RelatedInformation

New acoustic model for humpback whale sound production

The mechanism by which baleen whales (Mysticeti) produce sounds has remained largely unknown, due in part to our limited knowledge of the relationship between the sound-producing anatomy and the vocal characteristics of calls. Recent studies on mysticete anatomy indicate that the laryngeal vocal folds are the sound source, and the surrounding air spaces may play an important role in airflow, and sound modification or transduction. This current study offers a theoretical model to describe the mysticete vocal production system, which is much more complex than that of typical terrestrial mammal species. Metric data from laryngeal structures and air space volumes are combined with frequency and duration ranges defined by recordings of humpback whales off the coast of Madagascar. The resulting model delivers a prediction of sound unit durations and frequency formants that are constrained by the measurements of the trachea, laryngeal sac, and nasal cavities. Results predicted by the model are comparable to those obtained from real recordings. Errors between the frequencies of real vocalizations and the frequencies estimated using our theoretical model are less than 60Hz for the low frequency band. Then, this new model should hopefully advance our growing understanding of sound generation in humpback whales, and mysticetes in general.

From anatomy to acoustics, a study of the sound generation process in baleen whales (mysticetes)

The mechanism of baleen whale (mysticete) sound production is a topic of much interest, particularly as they make the loudest natural sounds and transmit them across the longest distances. Prior studies on mysticete sound generation have explored either acoustics or anatomy, but unfortunately have done so in isolation of the other discipline. This study links the two disciplines to derive a comprehensive understanding of the sound production process. Anatomical data (vocal fold measures, respiratory tract volumes, air flow paths) are used to derive initially an acoustic model that explains how sounds are made and transmitted. The model is then tested by comparisons to parameters (frequency, amplitude, duration) derived from hydrophone recordings of live whales. The model defines four mutually exclusive components: air sources (providing initial energy), vibrators generating harmonic frequencies (vocal folds, corniculate flaps), air flow paths (between lungs, trachea, laryngeal sac, nasal cavities), and radiating areas (transmitting sound energy to water). This model explains, for the first time, the acoustic function of each part of the mysticete sound generating system.Grant Funding Source: AAA

Anatomy to Acoustics: The Mechanism of Humpback Whale Sound Production

Humpback whales emit complex songs comprised of successive sound units with a fundamental frequency and harmonics. It is unknown how these calls are produced, given that the respiratory tract is closed (i.e., no egress of air from the nose or mouth) during underwater vocalizations. Unlike open system of terrestrial mammals, the whale vocal tract is subject to flow cessation as pressure builds. Prior studies on cetacean laryngeal anatomy (Reidenberg and Laitman, 2007) showed a communication for airflow between the trachea and an expandable ventral diverticulum called the laryngeal sac. We propose a theoretical model of humpback whale sound production based on the source‐filter theory that accounts for a closed system constrained by the dimensions of the trachea, the nasopharynx, and the laryngeal sac. We used recordings of humpback whales from the Indian Ocean (provided by Cetamada Association, Madagascar). Results show a relationship between time (duration) and spectral features (fundamental frequencies) of these calls. As this is a closed system, duration is dependent upon laryngeal sac pliability, while frequency is determined by vocal tract length. Our investigation is a first step towards defining individual acoustic signatures. Future studies will assess whether predicted durations and frequencies, based upon known vocal tract measures, fall within the range of actual recorded sounds.

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.

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.

Development of the Laryngeal Air Sac in Chimpanzees

Though many nonhuman primates possess a laryngeal sac, the great apes are unique in their great size. Though an enlarged sac probably arose in their common ancestor, its functional adaptations remain a matter of debate. Its development in extant great apes is likely to provide valuable information to clarify the issue. We used magnetic resonance imaging to examine the development of the laryngeal sac in 3 living chimpanzees, age 4 mo–5 yr, and identified 2 distinct growth phases of the sac. A gradual growth of the sac in early infancy results in a configuration so that it occupies the ventral region of the neck; many adult nonhominoid primates having a sac show the configuration. The subsequent rapid expansion of the sac in late infancy causes the final configuration in chimpanzees, wherein the sac expands into the pectoral, clavicular, and axillary regions. The latter phase possibly arose at latest in the last common ancestor of extant great apes and contributed to the evolution of the enlarged sac, despite the later evolutionary diversification in adult sac anatomy and growth. As many studies have advocated, the enlarged sac probably plays a role in vocalization in adults. However, physiological modifications in the laryngeal region during infancy are likely to provide valuable information to evaluate the functional adaptations of the enlarged sac in the great apes.

Anatomy of infrasonic communication in baleen whales: Divergent mechanisms of sound generation in mysticetes and odontocetes

Cetaceans produce sounds at opposite ends of the frequency spectrum. The laryngeal role in odontocete sound production (echolocation, communication) remains unclear. Mysticete infrasonics are presumed to be laryngeal in origin, but production mechanisms are unknown. To address this, we examined postmortem larynges in 6 mysticete species (3 genera) and compared them to our odontocete collection (20 species/15 genera). Results indicate that the rostral portion of the odontocete larynx is elongated, narrow, rigid, and normally positioned intranarially. This portion of the mysticete larynx is comparatively shortened, open, pliable, and in Megaptera may be retracted from its intranarial position. Internally, mysticete vocal folds are thick, paired, and oriented horizontally, compared with the thin, usually unpaired, and vertically oriented odontocete fold. Mysticetes may generate low frequency sounds via pneumatically driven fold vibrations, which then pass to attached laryngeal sac walls, through overlying throat pleats, to water. Rorqual mysticetes may also vibrate paired corniculate flaps while regulating airflow into the nasal region. Infrasonic pulses may pass through adjacent soft palate, skull, or nasal cartilages to water. Laryngeal anatomy in mysticetes and odontocetes appears highly divergent. These morphological differences may correlate to adaptations for producing infrasonic (mysticete) or ultrasonic (odontocete) communication. [Work supported by ONR:N00014-96-1-0764, ONR:N00014-99-1-0815, and AMNHSOF.]

Anatomy of the laryngeal apparatus of the Pygmy Right Whale,Caperea marginata (Gray 1846)

The laryngeal apparatus of Caperea marginata is described for the first time and proves to be significantly different from that of any mysticete previously described. This difference is especially noticeable in the position of the laryngeal sac, which is separate from the tracheal rings and lies to the right of the animal. Massive ontogenetic development of the sac in adult males is demonstrated, far greater than that seen in most other mysticetes. Histological analysis of the laryngeal sac shows the walls to be very muscular, abundantly innervated, and vascularized, indicating an active organ. Coiled blood vessels and nerves support the hypothesis that the sac undergoes extensive expansion and contraction. A possible association with the unique thoracic development of the species is suggested. The roles of the laryngeal sac and arytenoid cartilages in mysticete sound production are also discussed.

Anatomy of the laryngeal apparatus of the pygmy right whale, Caperea marginata (Gray 1846).

The laryngeal apparatus of Caperea marginata is described for the first time and proves to be significantly different from that of any mysticete previously described. This difference is especially noticeable in the position of the laryngeal sac, which is separate from the tracheal rings and lies to the right of the animal. Massive ontogenetic development of the sac in adult males is demonstrated, far greater than that seen in most other mysticetes. Histological analysis of the laryngeal sac shows the walls to be very muscular, abundantly innervated, and vascularized, indicating an active organ. Coiled blood vessels and nerves support the hypothesis that the sac undergoes extensive expansion and contraction. A possible association with the unique thoracic development of the species is suggested. The roles of the laryngeal sac and arytenoid cartilages in mysticete sound production are also discussed.

Microanatomy of the major airway mucosa of the bowhead whale, Balaena mysticetus.

In the bowhead whale, Balaena mysticetus, the mucosa of the major airways from the blowholes through the rostral portion of the larynx is lined with parakeratotic, pigmented, stratified squamous epithelium. Scattered enlarged connective tissue papillae of the lamina propria of the nasal vestibules and the palatopharyngeal sphincter contain encapsulated nerve endings. Abundant papillae in the mucosa covering the epiglottic and arytenoid cartilages contain similar nerve endings. The remainder of the laryngeal cavity and laryngeal sac is lined by a variably pigmented, stratified squamous epithelium, which is not keratinized. At the laryngotracheal junction the lining changes to ciliated pseudostratified columnar epithelium which continues through the trachea and principal bronchi. Scanning electron microscopy (SEM) indicates that this epithelium is typically mammalian, with approximately half of the surface cells bearing cilia and slender microvilli. The remaining cells are mucus producing and have thicker microvilli. The valvular mass regulating the external nares consists of irregular, dense white fibrous connective tissue with numerous adipose cells and is penetrated by skeletal muscle cords ranging from 2-4 mm in diameter. The septal mass between the blowholes is composed of irregular, dense white fibrous connective tissue containing large tendinous bundles, clusters of adipose cells, and several large arteries and thick-walled veins. The lamina propria of the nasal vestibules is irregular, dense white fibrous connective tissue. That of the larynx is not as dense and contains proportionately more elastic fibers. The laryngeal sac does not contain elastic laminae, but does have a tunica muscularis of skeletal muscle bundles. Within the trachea and principal bronchi, the lamina propria possesses laminae of longitudinally oriented elastic fibers and simple, branched tubuloalveolar mucous glands. The nasal, laryngeal, tracheal, and bronchial cartilages are hyaline with vascular channels.

Gross anatomy of the respiratory system of the bowhead whale, Balaena mysticetus.

Components of the respiratory system from seven bowhead whales have been examined. The paired and laterally curved external nares are passively closed by a valve-like mass located in the rostral, lateral, and ventral walls of the nasal vestibules. Nasal septal cartilages are paired smooth plates rostrally changing to accordion-like folds caudally. The epiglottic and arytenoidal protuberances of the larynx are typically cetacean, but blunt. The cricoid cartilage is not a complete ring, but an elongated, inverted, trough-shaped structure. The thyroid cartilage is trough-shaped with elongated cranial cornua curving dorsocaudally from each thyroid lamina. A conical mass of skeletal muscle serves as the floor of the short trachea and also surrounds the termination of the laryngeal sac. The trachea is dorsoventrally compressed, lacks a tracheal bronchus, and its width equals its length. The principal bronchi give rise to lobar bronchi at obtuse angles. Large segmental bronchi branch extensively from lobar bronchi near the mediastinal lung surface. The lungs are rectangular and of nearly uniform thickness throughout, without external or internal lobulation.

On Histology and Sensory Nerve Supply of Larynx in Flying-squirrel

The epithelium of the laryngeal side of the epiglottis of flying-squirrel is a stratified flat epithelium much thinner than that on its lingual side, but near its median line, it is a 5-6-rowed ciliatated epithelium. No papillae are formed beneath this stratified flat epithelium, as are found on the lingual side of the epiglottis. Taste-buds are found on the lingual side alone in small number. The mixed glands are well developed in the median and the peripheral parts of the laryngeal side. The epiglottic cartilage is of hyaline nature and forms one integral plate.The ventriculus laryngis forms a huge laryngeal sac, which reaches the inner surface of the thyroid cartilage on the ventral side, juts out toward the pharyngeal mucous membrane on the dorsal side, reaches the vicinity of the hyoid bone beyond the upper border of the thyroid cartilage on the cranial side and extends down to the upper end of the trachea on the caudal side. The sac is generally lined by a one-rowed cubic epithelium and partly by a 2-rowed cylindrical epithelium. The propria is very ill developed and mixed glands are found only in a limited area.The vocal cord consists in the main of 2-rowed stratified flat epithelium and a thin propria, but their ventralmost part alone is covered by a 2-3-rowed cylindrical or ciliated epithelium. The ventral one-third of the pars intercartilaginea of the rima glottidis is composed of a 2-rowed flat epithelium and a thin propria, but its dorsal tow-thirds are of a 2-3-rowed ciliated epithelium and subepithelial connective tissue gradually gaining in thickness dorsalwards and containing some mixed glands. The lower part of the larynx between the rima glottidis and the entrance to the trachea is composed of a 2-3-rowed ciliated epithelium and a subepithelial connective tissue layer containing mixed glands.The laryngeal mucous membrane of flying-squirrel is supplied with sensory fibres as in man, dog, goat and rabbit, but much less abundantly than in these, the submucosal and the proprial plexus found very well developed in these mammals being much inferior in flying-squirrel. The sensory nerve terminations are also much simpler in formation, no such corpuscular terminations or complex branched terminations as found in the above animals being ever to be found here.The sensory terminations found in the laryngeal mucous membrane of flying-squirrel are of unbranched and simple branched types formed either subepithelially or intraepithelially. Most primitive subepithelial unbranched terminations are found everywhere in the mucous membrane and in the laryngeal sac in particular most of the terminations are of this type, found here and there in sporadic existence. Thus, the sensory supply to the laryngeal sac may be called very poor in general, but near the entrance of the ventriculus laryngis subepithelial and intraepithelial simple branched terminations are not rare either. The terminal fibres of these terminations are sometimes comparatively thick and sometimes run wavy courses.The laryngeal side of the epiglottis is richest in sensory fibres, rather complex branched ones being found among their terminations, especially near its median line. Branched terminations with several terminal fibres are not rare here and some complex intraepithelial branched terminations are present, but the terminal fibres are usually medium-sized or thin, showing not much change in size. In the peripheral parts of the laryngeal side of the epiglottis, the sensory fibers are fewer and their terminations are simpler, but in these parts, simple brached terminations originating in thick fibres may be observed. Terminations formed by extraordinarily thick fibres, as found in man and rabbit, are never found in flying-squirrel.Sensory terminations are found on the border part between the laryngeal and the lingual sides of the epiglottis but their number decreases rapidly as we pass over into the lingual side