An Optimal Timing for Removing a Drain After Breast Surgery: A Systematic Review and Meta-Analysis.

BACKGROUND: In clinical practice, drains had been routinely used for reducing seroma formation after breast surgery. However, an optimal timing to remove drains does not identify yet. METHODS: This study aimed to compare the clinical outcome, such as seroma formation, surgical site infection (SSI), and a length of hospital stay between early removal and late removal. A systematic review was performed using PubMed, MEDLINE, and the Cochrane Library. Breast cancer patients who received surgery using drains were eligible. Those parameters were compared between early vs late removal. RESULTS: Eleven studies included in this meta-analysis. Seroma formation in the early removal group was significantly higher than the one in the late removal group (RR = 1.58: 95%CI [1.25-2.01], P = 0.0001), meanwhile no significant difference was found among the groups for SSI (RR = 0.82: 95%CI [0.51-1.31], P= 0.40). A length of hospital stay in the early removal group was also significantly shorter than late removal (RR -3.31: 95%CI [-5.13-1.49], P = 0.0004). CONCLUSIONS: Seroma formation was significantly higher in patients who had early drain removal. Conversely, SSI incidence was low, and early removal did not increase SSI incidence. In conclusion, early drain removal has no proved clinical benefit in these settings besides reduction of hospital stays.

Origin of enhanced boric acid adsorption in light-burned magnesium oxide.

Light-burned magnesium oxide (MgO) possesses a high surface area and has attracted interest as a promising candidate for boron adsorption materials; however, the detailed molecular structures decisive for enhancing the adsorption performance have not yet been elucidated. Here, the origin of enhanced boric acid adsorption for the light-burned MgO is studied by multiple probes, including positronium (Ps) annihilation spectroscopy, Fourier transform infrared spectroscopy, and sorption experiments coupled with molecular simulations. The state-of-the-art technique of open space analysis using Ps revealed the detailed structure of the interfaces between MgO nanograins: ∼10 Šand ∼30 Šopen spaces, participating in the chemisorption of B(OH)4 - and BO3 3- simultaneously with the physisorption of neutral B(OH)3 molecules. Furthermore, in addition to the fraction of open spaces, a proton quasi-layer formed on the interior surfaces of the above-mentioned angstrom-scale open spaces was identified to be attributable for enhancing both the chemisorption and physisorption.

Structural reconfigurations of nanosheet arrays in layered minerals caused by wave irradiation: desorption mechanism of Cs from nanosheet edges.

In layered minerals typically available in soil, there exists a high concentration of nanosheet edge sites formed by overlap among two-dimensional (2D) nanosheets, which act as heavily adhesive Cs chemisorption sites. Here, we propose the application of irradiation with ultrasonic waves in addition to microwaves employing ethylenediaminetetraacetic acid (EDTA) chelate to aid the decontamination of Cs from the nanosheet edges. The energy deposition by irradiation with both micro and ultrasonic waves is found to separate the overlap among the 2D nanosheets, succeeding in the desorption of Cs from the nanosheet edges. The decontamination of Cs became more prominent with ultrasonic irradiation owing to more efficient energy deposition than that with microwaves. The desorption mechanism is highlighted based on the results of systematic studies of the local structural reconfigurations of nanosheet arrays caused by wave irradiation. Surprisingly, not the aqueous solution nor interlayer water but constitution water triggers Cs desorption from the nanosheet edges, thus opening up a future decontamination strategy with a water saving system.

Heterogeneity of Stem Cells in the Human Vocal Fold Mucosa.

1. There is growing evidence to suggest that the cells in the maculae flavae are tissue stem cells of the human vocal fold and maculae flavae are a candidate for a stem cell niche. 2. The latest research shows that the cells in the human maculae flavae are involved in the metabolism of extracellular matrices that are essential for viscoelasticity in the human vocal fold mucosa as a vibrating tissue and are considered to be important cells in the growth, development, and aging of the human vocal fold mucosa. 3. Recent evidence has indicated that the cells including vocal fold stellate cells in the maculae flavae of the human vocal fold mucosa are a functionally heterogenous population. 4. The cells in the human maculae flavae possess proteins of all three germ layers, indicating that they are undifferentiated and have the ability of multipotency. 5. The cell division in the human adult maculae flavae is reflective of asymmetric self-renewal, and cultured cells form a colony-forming unit. Therefore, the phenomenon gives rise to the strong possibility that the cells in the human maculae flavae are putative stem cells. 6. Recent research has suggested that the cells in the human maculae flavae arise from the differentiation of bone marrow cells via peripheral circulation. 7. Cultured cell populations in the human maculae flavae are roughly divided into three groups by morphological features: cobblestone-like polygonal cells, vocal fold stellate cell-like cells, and fibroblast-like spindle cells. However, at the present state of our investigation, it is difficult to clarify the stem cell system and hierarchy of stem cells in the human maculae flavae. 8. Subpopulations of cells in the maculae flavae proliferate extremely slowly and retain stem cell properties. 9. Tension caused by phonation seems to regulate the behavior and heterogeneity of the cells (mechanical regulation) in the maculae flavae of the human vocal fold. 10. The putative stem cells in the maculae flavae appear to differentiate into other kind of cells in the surrounding tissue.

Pericytes in the Human Vocal Fold Mucosa.

1. The human vocal fold is a vibrating tissue and vascular structures in organs which have the capacity to vibrate require a specific structure suitable for vibration. 2. The structure of the blood vessels is unique at the vocal fold edge as a vibrating tissue, where only small vessels, including arterioles, venules, and capillaries, are present. The capillaries are distributed in the superficial layer of the lamina propria (Reinke's space). 3. The blood vessels enter the vocal fold edge from the anterior or posterior end of the membranous vocal fold and run essentially parallel to the vocal fold edge. 4. Many pericytes can be seen around the capillaries in the human vocal fold mucosa. The cell bodies of the pericytes attach to capillary endothelial cells, and the branching processes encircle the capillaries and attach to the capillary endothelial cells at the tips. The processes of pericytes are in close contact with endothelial cells, sharing a common basement membrane with them. The tips of the processes form intercellular tight junctions with endothelial cells. 5. The pericytes in the vocal fold mucosa appear to provide mechanical support and protection to the capillary walls, particularly during phonation. The pericytes also appear to regulate the diameter of the capillary during and after phonation. Pericytes are also thought to be critical cells in vascular biology and angiogenesis, especially in revascularization following vocal fold tissue injury. 6. At birth, pericytes have already encircled the capillaries in the newborn vocal fold mucosa. The pericytes appear ready to provide support and protection of the blood vessels just after birth. 7. Vascular structures and their permeability are related to the specific structures and specific diseases of the human vocal fold mucosa as a vibrating tissue.

Molecular studies of Cs adsorption sites in inorganic layered materials: the influence of solution concentration.

Radioactive Cs released into a soil environment migrates along with groundwater in a manner dependent on Cs concentration. Data on the variation of Cs adsorption as a function of solution concentration are an essential prerequisite to successful decontamination work in Fukushima. To aid the ongoing decontamination work, the adsorption of Cs in aqueous solution across a wide Cs+ molarity range is studied for the case of saponite clay as adsorbent, an inorganic layered material that is an abundant mineral in the soil environment. The local molecular structures, i.e. nanosheet surfaces, nanosheet edges, and oncoming hexagonal cavities, participating in Cs adsorption are qualitatively highlighted by means of a recently developed analytical method using data from a conventional elution test, 133Cs magic-angle-spinning nuclear magnetic resonance (MAS NMR), and the radiocesium interception potential (RIP) [K. Sato, et al., J. Phys. Chem. C, 2016, 120, 1270]. The concentrations of nanosheet edges amount to between 100 and 400 mmol kg-1, which are not substantially different from those of the nanosheet surfaces, generally regarded as the main decontamination sites. This unambiguously implies that the nanosheet edges should be targeted as the molecular sites for decontaminating radioactive Cs, in addition to the nanosheet surfaces.

The Macula Flava of the Human Vocal Fold as a Stem Cell Microenvironment.

1. There is growing evidence to suggest that the cells in the maculae flavae are tissue stem cells of the human vocal fold and maculae flavae are a candidate for a stem cell niche. 2. The latest research shows that the cells in the human maculae flavae are involved in the metabolism of extracellular matrices that are essential for the viscoelasticity in the human vocal fold mucosa as a vibrating tissue, and considered to be important cells in the growth, development, and aging of the human vocal fold mucosa. 3. The cells in the human maculae flavae possess proteins of all three germ layers, indicating they are undifferentiated and have the ability of multipotency. 4. The cell division in the human adult maculae flavae is reflective of asymmetric self-renewal and cultured cells form a colony-forming unit. Therefore, the phenomenon gives rise to the strong possibility that the cells in the human maculae flavae are tissue stem cells. 5. Recent research suggests that the cells in the human maculae flavae arise from the differentiation of bone marrow cells via peripheral circulation. 6. The hyaluronan concentration in the maculae flavae is high and contains cells which possess hyaluronan receptors, indicating that the maculae flavae are hyaluronan-rich matrix, which is required for a stem cell niche. 7. A proper microenvironment in the maculae flavae of the human vocal fold mucosa is necessary to be effective as a stem cell niche maintaining the stemness of the contained tissue stem cells.

Endoscopic surgical technique for benign fibrotic strictures of the upper esophageal sphincter.

A 43-year-old man with complaints of increased difficulty swallowing and weight loss underwent videofluorographic examination of swallowing, which revealed severely reduced cricopharyngeal opening. Endoscopic cricopharyngeal myotomy was carried out using a modified technique (mECPM). A benign fibrotic stricture of the upper esophageal sphincter (UES) was identified under visualization of a distending operating laryngoscope. A vertical midline incision in the strictured mucosa and submucosal resection of the cricopharyngeal muscle were done using a CO2 laser. The initial vertical mucosal incision was tightly sutured in the horizontal direction with absorbable surgical sutures. Histopathological examination of the cricopharyngeal muscle revealed infiltration of inflammatory cells. The patient started oral intake on postoperative day 7. He has been symptom free for 2 years with an improved body mass index, and postoperative laryngoscopy revealed no salivary retention in the piriform sinuses. The technique presented here provides sufficient opening of the UES by eliminating the problem of restenosis. mECPM will be useful for treating benign fibrotic strictures of the UES.

Origin of Vocal Fold Stellate Cells in the Human Macula Flava.

OBJECTIVES: There is growing evidence that vocal fold stellate cells (VFSCs) in the human maculae flavae are tissue stem cells of the human vocal fold and that the maculae flavae are a stem cell niche. The origin of the cells in the human maculae flavae (CHMF) and the relationship with bone marrow-derived cells were investigated. METHODS: Five human adult vocal fold mucosae were investigated. The CHMF were subcultured and morphological features were assessed. Immunoreactivity to antibodies directed to cytokeratin, desmin, GFAP, vimentin, CD34, CD45, and collagen type I was investigated. RESULTS: Cultured CHMF formed a colony-forming unit, indicating they are mesenchymal stem cells or stromal stem cells in the bone marrow. The CHMF expressed hematopoietic markers (CD34, CD45) and collagen type I, which are the major makers for bone marrow-derived circulating fibrocytes. The cultured CHMF expressed epithelium-associated, muscle-associated, neural-associated, and mesenchymal cell-associated proteins, indicating the CHMF are undifferentiated and express proteins of all 3 germ layers. CONCLUSIONS: The CHMF are undifferentiated cells derived from the differentiation of bone marrow cells. The results of this study are consistent with the hypothesis that the VFSCs are tissue stem cells or progenitor cells of the human vocal fold mucosa.

Mechanical regulation of human vocal fold stellate cells.

OBJECTIVE: It is generally accepted that tensile and compressive strains have direct effects on cell morphology and structure, including changes in cytoskeletal structure and organization. Cytoskeletons play the role of mechanoreceptor of the cells. Vocal fold stellate cells (VFSCs) in the human maculae flavae (MFe) are inferred to be involved in the metabolism of extracellular matrices essential for the viscoelasticity of the vocal fold mucosa. Our previous studies have supported the hypothesis that the tension caused by phonation (vocal fold vibration) regulates the behavior of the VFSCs. The microstructure of the intermediate filaments and the expression of their proteins were investigated in VFSCs in the MFe, which had remained unphonated since birth. METHODS: Three adult vocal fold mucosae that had remained unphonated since birth were investigated by immunohistochemistry and electron microscopy. RESULTS: The intermediate filaments of the VFSCs were fewer in number. The expression of their characteristic proteins (vimentin, desmin, and glial fibrillary acidic protein) was also reduced. CONCLUSION: Vocal fold vibration seems to affect VFSC morphology and structure, such as cytoskeletal structure and organization. This supports the hypothesis that vocal fold vibration regulates VFSC behavior in the human MFe. In addition to chemical factors, mechanical factors also appear to modulate VFSC behavior.

Long-term self-assembly of inorganic layered materials influenced by the local states of the interlayer cations.

A wide variety of parameters as, e.g., temperature, humidity, particle size, and cation state are known to influence the agglomeration process of two-dimensional (2D) nanosheets, called self-assembly, in inorganic layered materials. The detailed studies on which parameters are decisive and how they influence the self-assembly, however, have not been performed yet. Here, the long-term self-assembly was studied for layered stevensite and hectorite, and compared with our previous data of saponite for elucidating an influence of local states of the interlayer cations. The results were analyzed with respect to a recently established rheological model, in which 2D nanosheets migrate parallel to the layer direction aided by water molecules as lubricants [K. Sato et al., J. Phys. Chem. C, 2012, 116, 22954]. With decreasing the strength of the local electric fields facing to the interlayer spaces, cation positions split into two or three, which makes the distribution of water molecules more uniformly. These water molecules enhance the rheological motion of the 2D nanosheets parallel to the layer direction, thus accelerating the self-assembly process.

Analysis of passive motion of para- and retropharyngeal structures during swallowing using dynamic magnetic resonance imaging.

The purpose of this study was to analyze passive motion of the para- and retropharyngeal space (PRS) during swallowing using dynamic magnetic resonance imaging (MRI). We conducted a preliminary study involving 30 healthy volunteers who underwent dynamic MRI. Consecutive MRI axial images were obtained by examining the plane parallel to the hard palate at the level of the anterior inferior corner of C2. Anterior displacement of the posterior pharyngeal wall (PPW) was measured as a motion index of pharyngeal contraction. The displacement and internal angle of the bilateral external and internal carotid arteries (ECA and ICA) and the bilateral centroids of the PRS area, as well as the increase in PRS area, were calculated at rest and at maximum pharyngeal contraction. In most participants, the bilateral ECA, ICA, and centroids were anterointernally displaced by pharyngeal contraction. The normalized ECA displacement (r = 0.64, r (2) = 0.41), normalized ICA displacement (r = 0.60, r (2) = 0.37), and normalized centroid displacement (r = 0.43, r (2) = 0.19) were more than moderately positively correlated with the normalized PPW displacement. The normalized PRS area increase (r = 0.35, r (2) = 0.12) was weakly positively correlated with the normalized PPW displacement. These results revealed that PRS area increased as the ECA and ICA were drawn anterointernally via its passive motion by pharyngeal contraction.

[Odontogenic maxillary sinusitis caused by dental restoration].

We report herein on 5 patients with odontogenic maxillary sinusitis caused by a dental restoration (caries cutting, cavity preparation, inlay restoration). Odontogenic maxillary sinusitis was noted following dental restoration. Even though the pulp cavity and dental pulp were intact, the odontogenic maxillary sinusitis occurred caused by an apical lesion. Infection by way of the dentinal tubules was suggested to be a cause of the pathophysiology. Endoscopic sinus surgery was indicated in patients with intractable odontogenic maxillary sinusitis caused by the dental restoration. Cone-beam x-ray CT was useful for the accurate diagnosis of odontogenic maxillary sinusitis caused by a dental restoration. Physicians should thus be aware of the possibility that a tooth, which has undergone dental restoration, may cause odontogenic maxillary sinusitis.

Pathogenesis of Reinke's Edema of the Vocal Fold.

OBJECTIVES: The most frequent etiologic factor of Reinke's edema (RE) is considered to be smoking. However, the mechanism for the onset and development of the disease remains unclear. Hypoxia-inducible factor-1α (HIF-1α) is an oxygen-dependent transcriptional activator which plays crucial roles in angiogenesis in hypoxic microenvironments. HIF-1α induces the expression of vascular endothelial growth factor (VEGF) which involves angiogenesis and enhances vascular permeability. This study investigated the roles of HIF-1α in the pathogenesis of RE. METHODS: Surgical specimens of RE from patients who underwent endolaryngeal microsurgery were used. Normal vocal folds were used as a control group. Expression of HIF-1α and VEGF was analyzed by immunohistochemistry. Three-dimensional fine structures of the vessels in RE were investigated using correlative light and electron microscopy (CLEM) technique. RESULTS: HIF-1α and VEGF were broadly expressed in the stromal, inflammatory, and endothelial cells in the lamina propria of the vocal fold of RE. The expression of HIF-1α and VEGF of RE were significantly higher than in the lamina propria of the normal vocal fold mucosa. CLEM showed vascularization and telangiectasia and there were many dilated capillaries with thin endothelium not covered with pericytes indicating the vessels were fragile. CONCLUSION: Transcription factor HIF-1α and induced VEGF likely play roles in the pathogenesis of RE. And increased vascular permeability with fragile vessels in angiogenesis is likely to be an etiology of RE. Transcription factor HIF-1α and induced VEGF are potential therapeutic targets for RE. LEVEL OF EVIDENCE: NA Laryngoscope, 134:1785-1791, 2024.

Growth and development of epiglottis and preepiglottic space of larynx as it acquires vocal tract.

Objectives: The growth and development of the epiglottis and preepiglottic space (PES) of the human larynx as it acquires the vocal tract were investigated. Methods: Three newborns, one infant, four children (2, 7, 8, and 12 years old), and two adult normal larynges were investigated and compared using the whole organ serial section technique. Results: The newborn PES occupied a small area just anterior to the epiglottis. It was composed of immature adipose tissue and areolar tissue. The epiglottis lay on a somewhat horizontal axis and is partially obscured behind the hyoid bone. The hyoid bone overlapped the thyroid cartilage, partially obscuring the superior thyroid notch. The newborn epiglottic cartilage was immature elastic cartilage, and the elastic fiber component was sparse. In the first 8 years of life, as the PES grew, the PES was located not only anterior to but also posterolateral and inferolateral to the epiglottic cartilage and thyroepiglottic ligament. Meanwhile, the epiglottic cartilage matured. Conclusions: In order to develop the vocal tract for speech production, it is reported that the human larynx descends as the child grows in the first 9 years of life. This study showed that the PES, occupying a small area just anterior to the epiglottis, grew and existed astride the epiglottis as the larynx descended and the vocal tract developed. Consequently, its distribution allows the epiglottis to more effectively play the role of retroflection during swallowing in order to prevent aspiration. The human speech faculty likely develops in conjunction with swallowing physiology.

Relationship between Swallowing Pressure and Saliva Residue on Endoscopic Evaluation in Pharyngeal Dysphagia.

OBJECTIVE: In pharyngeal dysphagia, poor pharyngeal contraction and upper esophageal sphincter (UES) dysfunction result in post-swallow saliva residue (SR). This study aimed to clarify the relationship between swallowing pressure and SR in the valleculae and piriform sinuses on flexible endoscopic evaluation of swallowing (FEES). METHODS: Pharyngeal dysphagia patients with Wallenberg syndrome were included. Amounts of post-swallow SR in the valleculae and piriform sinuses were classified into four grades using SR scores based on FEES. The Hyodo score was also calculated to evaluate swallowing function. High-resolution manometric data in the nasopharyngeal, oropharyngeal, hypopharyngeal, oro-hypopharyngeal, and UES zones on swallowing were obtained for comparison with SR and Hyodo scores. RESULTS: Of the 31 recruited, data from 26 patients who successfully underwent FEES and manometry were analyzed. Vallecular SR scores were strongly negatively correlated with a maximum pressure of the oropharynx (r = -0.52, p = 0.006), distal contractile integrals (DCI) of the oropharynx (r = -0.52, p = 0.007), and DCI of the oro-hypopharynx (r = -0.55, p = 0.004). Hyodo scores for parameters 1 and 4 (corresponding to salivary pooling and pharyngeal clearance, respectively) were strongly negatively correlated with a maximum hypopharyngeal pressure (r = -0.57, p = 0.002) and strongly positively correlated with peristaltic velocity (r = 0.53, p = 0.007), respectively. SR scores and Hyodo scores related to SR were not correlated with pressure data of the UES. CONCLUSION: Manometric analysis of our SR scoring method using FEES revealed that a higher amount of SR in the valleculae, but not in the piriform sinuses, is associated with weaker pharyngeal pressure in pharyngeal dysphagia, especially at the oropharyngeal level. LEVEL OF EVIDENCE: 4 Laryngoscope, 134:3519-3526, 2024.

Twin vocal folds as a novel evolutionary adaptation for vocal communications in lemurs.

Primates have varied vocal repertoires to communicate with conspecifics and sometimes other species. The larynx has a central role in vocal source generation, where a pair of vocal folds vibrates to modify the air flow. Here, we show that Madagascan lemurs have a unique additional pair of folds in the vestibular region, parallel to the vocal folds. The additional fold has a rigid body of a vocal muscle branch and it is covered by a stratified squamous epithelium, equal to those of the vocal fold. Such anatomical features support the hypothesis that it also vibrates in a manner like the vibrations that occur in the vocal folds. To examine the acoustic function of the two pairs of folds, we made a silicone compound model to demonstrate that they can simultaneously vibrate to lower the fundamental frequency and increase vocal efficiency. Similar acoustic effects are achieved using different features of the larynx for the other primates, e.g., by vibrating multiple sets of ventricular folds in several species and further by an evolutionary modification of enlarged larynx in howler monkeys. Our multidisciplinary approaches found that these functions were acquired through a unique evolutionary adaptation of the twin vocal folds in Madagascan lemurs.

Optimized graded index two-mode optical fiber with low DMD, large A(eff) and low bending loss.

An optimized two-mode optical fiber (TMF) with the graded index (GI) profile is designed and fabricated. We clarify an appropriate region of GI-TMF satisfying DMD = 0 ps/km, the large effective area A(eff), and the low bending loss for LP(11) at 1550 nm. According to our fiber design, GI-TMF is successfully fabricated to have the large effective area A(eff) of 150 µm(2) for LP(01) mode, and low DMD below 36 ps/km including zero in the C-band. We expect that our design GI-TMF is suitable for MDM and can reduce MIMO-DSP complexity.

Vascularity in the macula flava of human vocal fold as a stem cell niche.

OBJECTIVES: There is growing evidence that the maculae flavae of the human vocal fold are a stem cell niche, which is a microenvironment nurturing tissue stem cells. This study investigated the microenvironment, especially vascularity, in the maculae flavae of the human vocal fold. METHODS: Three normal human adult, three normal newborn vocal folds obtained from autopsy cases and three surgical specimens of glottic carcinoma were investigated using light and electron microscopy. For scanning electron microscopy, a chemical digestion method (modified sodium hydroxide maceration method) was used to observe the inner 3-dimensional structure of the macula flava. RESULTS: Capillaries ran around the anterior and posterior maculae flavae in adults and newborns. However, there was no vascularity in the maculae flavae of the vocal fold. The inner 3-dimensional electron microscopic structure of the macula flava showed there were no blood vessels in the maculae flavae of the vocal fold. Glottic carcinoma (squamous cell carcinoma) surrounded and was in contact with the macula flava, however, the carcinoma did not invade the macula flava indicating there was no vascular supply into the macula flava from the surrounding tissue. CONCLUSIONS: There was no vascularity in the anterior and posterior maculae flavae in the human adult and newborn vocal folds. The present study is consistent with the hypothesis that the hypoxic microenvironment in the maculae flavae of the adult and newborn vocal fold as a stem cell niche is likely favorable to maintaining the stemness and undifferentiated states of the tissue stem cells in the stem cell system.

Comparative Histoanatomy of the Epiglottis and Pre-epiglottic Space of the Chimpanzee Larynx.

OBJECTIVES: Understanding of the evolution of the larynx clarifies the physiology and functional histoanatomy of the present-day human organ. Comparative histoanatomy of the epiglottis and pre-epiglottic space of the chimpanzee larynx (a hominid, phyletic closest relative of humans) was investigated. METHODS: Two normal adult chimpanzee larynges obtained from natural deaths were investigated. The whole organ serial section technique was employed. RESULTS: The histoanatomical structures of the chimpanzees' epiglottis and pre-epiglottic space were considerably similar to those of human adults. The chimpanzees' epiglottic cartilage was relatively thin and composed of elastic cartilage. These histologic findings of epiglottis indicate that the chimpanzee's epiglottis is flexible and plays the role of retroflection. The chimpanzees' larynges had a pre-epiglottic space composed of adipose tissue and loose connective tissue. Epiglottic cartilage was connected to the thyroid cartilage anteroinferiorly with an intervening thyroepiglottic ligament and to the hyoid bone anteriorly with an intervening hyoepiglottic ligament. These histoanatomical structures of the epiglottis and pre-epiglottic space reflect the fact that chimpanzees have a descended larynx and acquire the pharyngeal space of the vocal tract. CONCLUSION: The results of this study are consistent with the hypothesis that, in the process of evolution, the histoanatomical structures of the epiglottis and pre-epiglottic space change and allow the larynx to descend and lengthen the pharyngeal space of the vocal tract which facilitates speech production in humans. Moreover, the distribution of the human pre-epiglottic space likely allows the epiglottis to more effectively play the role of retroflection during swallowing in order to prevent aspiration.