Ultrasound Evaluation of Anterior Neck Soft-Tissue Thickness to Predict Difficult Intubation in Overweight Adult Patients Posted for Surgery under General Endotracheal Anesthesia - An Observational Study.

BACKGROUND: Ultrasonographic imaging has been recently become simple portable and non-invasive adjuvant for bedside assessment of anterior neck soft tissue thickness which when measured at different levels showed to have significant role in predicting difficult laryngoscopy. AIMS AND OBJECTIVES: Primary objective was Ultrasonographic measurement of anterior neck soft tissue thickness at 3 levels -Distance from skin to hyoid bone (DSHB) -Distance from skin to thyrohyoid membrane (DSTM) -Distance from skin to anterior commissure of vocal cord(DSAC) and to compare and correlate the findings with Cooks modification of Cormack-Lehane score in predicting difficult laryngoscopy. Secondary objective was to compare and correlate the ultrasonographic measurements with conventional airway assessment methods. MATERIALS AND METHODS: After obtaining approval from the ethical committee, 90 Patients with BMI above 25 kg /m2 was enrolled for the study. A day before the surgery a thorough Preanaesthetic evaluation and assessment of the airway is done using conventional methods. Then on the day of surgery ultrasonographic measurement of anterior neck at 3 levels was done and after inducing the patients laryngoscopy was done and Cooks modification of Cormack-Lehane score assessed. RESULTS: The optimal cut off values to predict difficult laryngoscopy was 1.26, 2 and 1.2 cms for DSHB, DSTM and DSAC respectively, and among the three skin to anterior commissure of vocal cord was observed to be best USG parameter with more area under the ROC curve. CONCLUSION: USG measurement of anterior neck soft tissue thickness can be useful in predicting difficult laryngoscopy in overweight and obese patients also it had more diagnostic accuracy than conventional methods like MMS in predicting difficult laryngoscopy.

RésuméArrière-plan L'imagerie échographique est récemment devenue un simple adjuvant portable et non invasif pour l'évaluation au lit du patient de l'épaisseur des tissus mous du cou antérieur qui, lorsqu'elle est mesurée à différents niveaux, s'est avérée avoir un rôle important dans la prédiction d'une laryngoscopie difficile. Buts et objectifs L'objectif principal était la mesure échographique de l'épaisseur des tissus mous du cou antérieur à 3 niveaux -Distance de la peau à l'os hyoïde (DSHB) -Distance de la peau à la membrane thyrohyoïdienne (DSTM) -Distance de la peau à la commissure antérieure de la corde vocale (DSAC) et pour comparer et corréler les résultats avec la modification de Cooks du score de Cormack-Lehane pour prédire une laryngoscopie difficile. L'objectif secondaire était de comparer et de corréler les mesures échographiques avec les méthodes conventionnelles d'évaluation des voies respiratoires Matériels et méthodes Après avoir obtenu l'approbation du comité d'éthique, 90 patients présentant un IMC supérieur à 25 kg/m2 ont été inclus dans l'étude. Un jour avant la chirurgie, une évaluation préanesthésique approfondie et une évaluation des voies respiratoires sont effectuées à l'aide de méthodes conventionnelles. Ensuite, le jour de la chirurgie, une mesure échographique de la partie antérieure du cou à 3 niveaux a été effectuée et après l'induction des patients, une laryngoscopie a été effectuée et la modification de Cooks du score de Cormack-Lehane a été évaluée. Résultats Les valeurs seuil optimales pour prédire une laryngoscopie difficile étaient respectivement de 1,26, 2 et 1,2 cm pour DSHB, DSTM et DSAC, et parmi les trois paramètres de la peau à la commissure antérieure de la corde vocale, il a été observé que le meilleur paramètre USG avec plus de surface sous la courbe ROC Conclusion La mesure par USG de l'épaisseur des tissus mous du cou antérieur peut être utile pour prédire une laryngoscopie difficile chez les patients en surpoids et obèses. Elle a également une plus grande précision diagnostique que les méthodes conventionnelles comme le MMS pour prédire une laryngoscopie difficile.

The skull of the Turks and Caicos rock iguana, Cyclura carinata (Squamata: Iguanidae).

We provide a detailed and first description of the skull, hyoid apparatus, and trachea of the Turks and Caicos rock iguana, Cyclura carinata (Squamata: Iguanidae). Cyclura is a radiation of iguanas restricted to islands of the Caribbean Sea. Species of Cyclura have high rates of endemism, and all species are severely threatened with extinction. Our anatomical description of this threatened iguana is based on high-resolution computed tomography scans of one adult, one putative adult or near adult, and one juvenile specimen, and includes three-dimensional segmented renderings and visualizations. We discuss some observations of intraspecific and ontogenetic variation, and provide a brief comparison with specimens of another species of Cyclura and published descriptions of other iguanas. Our study provides a cranial osteological framework for Cyclura and augments the body of knowledge on iguana anatomy generally. Finally, we posit that our description and future studies may facilitate identification of fossil Cyclura, which could help understand the paleobiogeography of the genus.

The previously undescribed variant of the thyrohyoid muscle and its potential impact on surgical procedures.

The thyrohyoid muscle belongs to the infrahyoid group located in the carotid triangle. It normally originates from thyroid cartilage and inserts into hyoid bone. Quite often, it is continuous with the sternohyoid muscle. Furthermore, there are variants that have their origin in the cricoid cartilage only, however, this occurs very rarely. During anatomical dissection, a two-headed variant of this muscle was found. One head had its origin in the cricoid cartilage and the other in the thyroid cartilage. This variant of thyrohyoid had not been previously described in the available literature. Therefore, we believe that it may be referred to as the cricothyrohyoid muscle. As the thyrohyoideus is often used as a landmark during surgical procedures in the prelaryngeal area and as a muscle graft, a thorough knowledge of its anatomy and variation is extremely important. We speculate that the two-headed version of this muscle may be problematic during surgical procedures in this region, however, it may also provide more options as a muscular graft.

Growing stylohyoideus muscle insertion to the hyoid bone with special reference to its topographical relation to the intermediate tendon of digastricus muscle: A histological study using human fetuses.

BACKGROUND: In adults, the intermediate tendon of digastricus muscle usually runs along the medial or lateral side of the stylohyoideus muscle insertion. To provide a better understanding of the variations, we examined the topographical anatomy of the muscle and tendon in fetuses. METHODS: We examined histological sections from six early-term, 26 mid-term and six near-term fetuses (approximately 8-9, 12-18 weeks and 25-33 weeks). RESULTS: At early-term, an initial sheath of intermediate tendon of digastricus muscle received the stylohyoideus muscle at the superior aspect. The muscle and tendon was distant from the hyoid. At mid-term, near the insertion to the hyoid greater horn, the stylohyoideus muscle consistently surrounded more than 2/3 of the intermediate tendon circumference. In contrast, we found no near-term specimen in which the stylohyoideus muscle surrounded the intermediate tendon. The multilayered tendon sheath was fully developed until near-term and connected to the body of hyoid by an intermuscular septum between the thyrohyoideus muscle and one or two of suprahyoid muscles. Therefore, the hyoid insertion of the styloglossus muscle was a transient morphology at mid-term. CONCLUSION: The stylohyoideus muscle insertion was appeared to move from the tendon sheath to the hyoid greater horn and, until near-term, return to the tendon sheath. A fascia connecting the tendon sheath to the body of hyoid was strengthened by the suprahyoid and infrahyoid muscles. The latter muscles seemed to regulate fixation/relaxation of the intermediate tendon to the hyoid. The stylohyoideus muscle slips sandwiching the intermediate tendon might be a rare morphology.

Sex estimation from the hyoid bone measurements in an adult Eastern Turkish population using 3D CT images, discriminant function analysis, support vector machines, and artificial neural networks☆.

The hyoid bone is one of the bones in the human body that shows sexual dimorphism. The anthropological and anthropometric characteristics that determine sexual dimorphism are influenced by demographic differences. The aim of this study was to investigate the rate of sexual dimorphism of the hyoid bone in the adult Eastern Turkish population from the examination of the 3D computed tomography images of 240 patients, using discriminant function analysis (DFA), support vector machines (SVM), and artificial neural networks (ANN). These evaluations were based on eight hyoid measurements that have been frequently used in previous CT studies. The results showed that all eight measurements were higher in males than in females (p = 0.000). It was determined that sex could be estimated accurately at up to 93.3 % using DFA, 93.8 % using SVM and 95.4 % using ANN. The maximum accuracy rate achieved to 94.2 % in males using SVM, and 95.8 % in females using ANN. These high rates of sexual dimorphism found using DFA, SVM, and ANN in this study indicate that characteristics of the hyoid bone can be utilized to determine sex in the Eastern Turkish population.

Evaluation of the influence of hyoid bone position, volume, and types on pharyngeal airway volume and cephalometric measurements.

OBJECTIVES: We aimed to explore the position, morphological, and morphometric properties of the hyoid bone (HB) and to investigate the effect of HB on the pharyngeal airway (PA) volume and cephalometric measurements. METHODS: A total of 305 patients with CT images were included in the study. DICOM images were transferred to the InVivoDental three-dimensional imaging software. The position of the HB was determined based on the cervical vertebra level and in volume render tab, the bone was classified into six types after all structures around the HB were removed. Also, final bone volume was recorded. In the same tab, the pharyngeal airway volume was divided and measured in three groups (nasopharynx-oropharynx-hypopharynx). The linear and angular measurements were performed on the 3D cephalometric analysis tab. RESULTS: HB was most commonly located in C3 vertebra level (80.3%). While B-type was found to be the most frequent (34%), V-type was the least frequent (8%). The volume of the HB was found to be significantly higher in male (3205 mm3) than female (2606 mm3) patients. Also, it was significantly higher in the C4 vertebra group. The vertical height of the face was positively correlated with the HB volume, C4 level position, and increased oro-nasopharyngeal airway volume. CONCLUSION: The volume of the HB is found to differ significantly between genders and can potentially serve as a valuable diagnostic tool for understanding respiratory disorders. Its morphometric features are associated with increased face height and airway volume; however, are not related with the skeletal malocclusion classes.

Evaluation of pharyngeal airway space after orthodontic extraction treatment in class II malocclusion integrating with the subjective sleep quality assessment.

Orthodontic treatment with premolar extractions is typically used to relieve dental crowding and retract anterior teeth for lip profile improvement. The aim of the study is to compare the changes in regional pharyngeal airway space (PAS) after orthodontic treatment with Class II malocclusion and to identify the correlations between questionnaire results and PAS dimensions after orthodontic treatment. In this retrospective cohort study, 79 consecutive patients were divided into normodivergent nonextraction, normodivergent extraction, and hyperdivergent extraction groups. Serial lateral cephalograms were used to evaluate the patients' PASs and hyoid bone positions. The Pittsburgh Sleep Quality Index and STOP-Bang questionnaire were used for sleep quality evaluation and obstructive sleep apnea (OSA) risk assessment, respectively, after treatment. The greatest airway reduction was observed in hyperdivergent extraction group. However, the changes in PAS and hyoid positions did not differ significantly among three groups. According to questionnaire results, all three groups had high sleep quality and low risk of OSA, with no significant intergroup differences. Moreover, pretreatment-to-posttreatment changes in PAS were not correlated with sleep quality or risk of OSA. Orthodontic retraction with premolar extractions nither exhibit significant reduction in airway dimensions nor increase their risk of OSA.

Radiological morphometric study of the hyoid bone using three-dimensional computed tomography (3D-CT) scans / Estudio morfométrico radiológico del hueso hioides mediante tomografía computarizada tridimensional (3D-CT)

SUMMARY: Hyoid bone measurements have been proposed to vary between different genders and age groups. The aim of the study is to study hyoid morphometrics among Jordanian patients. 3D-CT scans of 637 patients were analyzed. Ten parameters of hyoid bone were measures, including the anteroposterior length, length of greater horns (right and left), height of greater horns (right and left), width of hyoid body, height of hyoid body, the distance between the midpoints of the posterior ends of the greater horns of the hyoid bone, the angle between right and left greater horns, and the distance of the hyoid bone to the vertebral column. Also, vertebral level, fusion rank, morphology of hyoid body lingula, and shape of hyoid bone were documented. All hyoid dimensions were longer in males, but greater horns angle was wider in females. In patients younger than 30 years, the parameters are the smallest with the widest angle. The distance from hyoid to vertebral column is higher in males (30-49) years of age. No fusion between hyoid body and greater horns was observed in patients younger than 10 years, but fusion (unilateral or bilateral) was found in only 73.2 % of patients ≥ 70 years. The hyoid was mostly at vertebra C3 level and "U" shaped. The lingula shape was mostly "Scar" in males (especially ≥ 50 years) and "Nothing" in females (especially < 50 years). The maximum growth of hyoid dimensions is before age of 30 years. Fusion between hyoid body and greater horns was not seen in patients younger than 10 years. Otherwise, the hyoid features failed to predict age or gender in our sample. Furthermore, 3D-CT scan is an excellent tool to assess the anatomy of head and neck region.

Se ha propuesto que las medidas del hueso hioides varían entre los diferentes sexos y grupos de edad. El objetivo del estudio fur estudiar la morfometría del hueso hioides en pacientes jordanos. Se analizaron tomografías computarizadas en 3D de 637 pacientes. Se midieron diez parámetros del hueso hioides, incluyendo la longitud anteroposterior, la longitud de los cuernos mayores (derecho e izquierdo), la altura de los cuernos mayores (derecho e izquierdo), el ancho del cuerpo hioides, la altura del cuerpo hioides, la distancia entre los puntos medios de los extremos posteriores de los cuernos mayores del hueso hioides, el ángulo entre los cuernos mayores derecho e izquierdo, y la distancia del hueso hioides a la columna vertebral. Además, se documentaron el nivel vertebral, el rango de fusión, la morfología de la língula del cuerpo hioides y la forma del hueso hioides. Todas las dimensiones del hioides fueron más largas en los hombres, pero el mayor ángulo de los cuernos fue más ancho en las mujeres. En pacientes menores de 30 años, los parámetros son los más pequeños con el ángulo más amplio. La distancia del hioides a la columna vertebral es mayor en el sexo masculino (30-49) años. No se observó fusión entre el cuerpo hioides y los cuernos mayores en pacientes menores de 10 años, pero se encontró fusión (unilateral o bilateral) en solo el 73,2 % de los pacientes ≥ 70 años. El hioides estaba mayormente al nivel de la vértebra C3 y en forma de "U". La forma de la língula era mayoritariamente "Cicatriz" en los hombres (especialmente ≥ 50 años) y "Nada" en las mujeres (especialmente < 50 años). El máximo crecimiento de las dimensiones del hioides es antes de los 30 años. La fusión entre el cuerpo hioides y los cuernos mayores no se observó en pacientes menores de 10 años. No obstante, las características del hueso hioides no pudieron predecir la edad o el sexo en nuestra muestra. Además, la tomografía computarizada 3D es una herramienta excelente para evaluar la anatomía de la región de la cabeza y el cuello.

More than two - A cadaveric study on the morphometry and classification of the digastric muscle in a selected kenyan population.

BACKGROUND: This study aims to elucidate anatomical variations of the digastric muscle in the Kenyan population. METHODS: A total of 41 bilateral neck dissections were performed whereby morphologic observations and morphometric measurements were carried out to characterize and classify the various presentations of the muscle. RESULTS: All cadavers presented with bilateral anterior (ABDM) and posterior (PBDM) bellies of the digastric muscle. Accessory ABDM was observed in 68.3% of cadavers with De-Ary-Pires et al.'s Type II (one accessory belly; 48.8%) and Type III (two accessory bellies; 34.1%) being the most common variations. Unilateral accessory ABDM (43.9%) was more common than bilateral accessory ABDM (24.4%). Two cadavers presented with a mentohyoid muscle. In addition, variations that have not been previously reported, namely fusion of ABDM to the midline and insertion of accessory ABDM into the hyoid bone were observed in one case each. Variation of the PBDM was less prominent, observed at 12.2% of sides dissected. Duplication of PBDM was observed on 4 sides with origin at the mastoid process. The PBDM was longer than the ABDM, but narrower in width. The mean length and width of the ABDM were 4.29±0.72cm and 1.52±1.07cm. The mean length and width of the PBDM were 5.64±1.31cm and 1.07±0.28cm, with the right side being statistically larger than the contralateral side. CONCLUSION: Variations of the digastric muscle are a common finding, with a high incidence at the ABDM. Two new variants were discovered.

Surgical landmarks for identification and preservation of the internal branch of the superior laryngeal nerve.

OBJECTIVE: To determine the topographical anatomic features of the internal branch of the superior laryngeal nerve (ibSLN) at the thyrohyoid membrane entrance area in relation to certain consistent anatomical structures. MATERIALS: METHODS: Twenty-two fresh adult head cadavers (9 male, 13 female; age range 52-95 years) with no signs of abnormality in the neck were dissected to determine the anatomic relationship of ibSLN and superior border of thyroid cartilage, thyroid notch, carotid bifurcation, hyoid corpus, and hyoid greater cornu. RESULTS: The topographical relationship between ibSLN and superior border of thyroid cartilage, thyroid notch, carotid bifurcation, hyoid corpus, and hyoid greater cornu was identified bilaterally in all cadavers. According to the measures, danger zone and safe zone areas for surgical could be predicted and for surgical manipulations as well. CONCLUSION: We provided the surgical anatomy and important landmarks for determining the internal branch of superior laryngeal nerve in the thyrohyoid membrane entrance region to avoid surgical damage during surgeries of this region.

[Study on the thickness and morphology of lingual bone of impacted mandibular third molar based on CBCT and Simplant 3D reconstruction].

PURPOSE: The potential relationship between impacted mandibular third molar and lingual bone thickness was investigated by quantitative measurement of lingual bone thickness, and a three-dimensional visualization model of lingual bone was established. METHODS: Image data of 200 cases of mandibular impacted third molar were collected from the database of Hefei Stomatological Hospital. Thickness measurement and three-dimensional reconstruction of lingual bone at different measurement sites were performed by Simplant Pro software. Statistical analysis was performed using SPSS 22.0 software package, and the comparison of lingual thickness at different measurement sites was performed using rank sum test. Whether the thickness of bone plate was "high-risk type" was taken as the result variable, different related factors were analyzed by logistic regression. RESULTS: The lingual bone at the middle point of the root of the third molar was the thinnest. Multiple teeth, mesio-inclined and dial-inclined teeth, and Class Ⅱ and Ⅲ impacted teeth had thin lingual bone(P＜0.05). The mesial and distal inclines were observed, and the lingual bone was thin in the root apical region of the teeth in Class Ⅱ and Class Ⅲ(P＜0.05). In the lower impacted teeth, the thin lingual bone at the central crown site was more likely to be found in Class Ⅲ teeth(P＜0.05). CONCLUSIONS: The thickness of lingual bone was related to the number of impacted tooth roots, tilt direction and impacted type. In the extraction of impacted teeth, the above factors should be considered, and the injury of lingual nerve, lingual bone and surrounding soft tissue should be vigilant.

The Hyoid Bone - the Anatomy of a Small Bone of the Neck in Hellenic and Greco-Roman Medical Literature.

OBJECTIVES: To understand the nomenclature of the hyoid bone. MATERIALS AND METHODS: Hyoid, a small bone of the neck, is a bony part that is rather difficult to unearth and discover among skeletal remains. RESULTS: The named was coined by the ancient Greeks, along with its anatomic description. Galen (2nd - 3rd c. AD) and Theophilus Protospatharius (7th century AD), facing religious and social barriers, succeeded in presenting its anatomy and suggesting its probable function in speech and swallowing, regarding the bone as a muscle pillar of the neck area. CONCLUSION: Authorities of Hellenic antiquity surprise us with their accuracy and the resilience of their anatomical descriptions.

Effect of premolar extraction on upper airway volume and hyoid position in hyperdivergent adults with different mandibular length.

INTRODUCTION: The objective of this study was to investigate the morphological changes of the upper airway and the position of the hyoid bone in hyperdivergent adults with different mandibular lengths after premolar extraction. MATERIALS: The data of 57 hyperdivergent adults, aged 20-35 years, who had 4 premolar extractions were included for the study. Mandibular length (CoGn) was used for grouping (A: long CoGn, B: short CoGn). Pretreatment and posttreatment lateral cephalograms and cone-beam computed tomography images were used to assess the position of mandible, hyoid bone, and upper airway using paired t test. An independent sample t test was used to detect changes of the airway and hyoid position between groups A and B. Pearson correlation analysis was applied to estimate the correlation between pharyngeal spaces and dentoskeletal morphology at P <0.05. RESULTS: In all subjects, we observed retraction of the upper incisors, mesial movement of the lower molars, and reduction of the mandibular planes. In group A, differences were found in anterior and posterior movements of the hyoid bone, increase of airway volume, minimum cross-sectional area (MCA) and anteroposterior linear distance (APL) (P <0.05). There were notable differences in the change of hyoid position, airway volume, MCA, and APL between group A and group B. Glossopharyngeal and hypopharyngeal volumes, MCA, and APL were correlated with articular angle, mandibular plane, and hyoid bone position (P <0.05). CONCLUSIONS: With a comprehensive diagnosis and treatment, premolar extraction in hyperdivergent adults with favorable CoGn can facilitate improvement of esthetics, hyoid bone position, and the increase in glossopharyngeal and hypopharyngeal volumes and MCA.

The use of hyoid bone dimensions in age and sex estimation in a Turkish population: a cone-beam computed tomography study.

BACKGROUND: The aim of the study was to determine sex and age from hyoid bone morphology on cone-beam computed tomography (CBCT). MATERIALS AND METHODS: The study sample comprised 130 CBCT images. Eight different measurements were performed for each hyoid bone. Fusion conditions were assigned to each side of the hyoid bone separately as; unfused, partially fused, and totally fused. RESULTS: The hyoid length, width of the left proximal end and stature variables showed sexual dimorphism in all hyoid fusion types (p < 0.05). In young adult age group, a significant difference was found between sex and fusion types (p = 0.025). The body length (81.35%) and stature measurements (76.25%) contributed most significantly to sex estimation. CONCLUSIONS: Patient's CBCT scans which enable reproducible and reliable measurements for bone tissues can be used for forensic procedures. Hyoid bone measurements with CBCT are useful methodology for age and sex estimation in forensic sciences with high predictive accuracy.

Cranial anatomy of the Galápagos marine iguana Amblyrhynchus cristatus (Squamata: Iguanidae).

Amblyrhynchus cristatus, the marine iguana, is unique among the ~7,000 species of living limbed lizards as it has successfully evolved adaptations that allow it to live in both terrestrial and marine environments. This species is endemic to the Galápagos Archipelago and has evolved a specialized feeding behavior, consuming primarily the algae that grow on the rocky seafloor. The intriguing questions arising around the evolution of the marine iguana concerns the use of exaptations of terrestrial features for aquatic and specifically marine adaptations. However, the lack of fundamental information about its anatomy currently prevents us from understanding how it became adapted to such a peculiar lifestyle in comparison to all other iguanids. The goal of this study is to provide the first ever description of the skull, mandible, and hyoid of Amblyrhynchus. We examined several specimens of marine iguana, including skeletal, wet, and ct-scanned material, and individuals at different ontogenetic stages. We also analyzed specimens of all other modern iguanid genera (Conolophus, Iguana, Ctenosaura, Cyclura, Dipsosaurus, Brachylophus, Sauromalus) in order to make comparisons between Amblyrhynchus and its closest relatives. We were able to identify several autapomorphic features that distinguish the marine iguana from all other iguanids. These unique morphologies are mostly associated with the modified configuration of the snout (nasal chamber), increased muscle attachments in the temporal-postorbital region of the skull, and dentition. Since Amblyrhynchus is the only nonophidian squamate currently able to exploit the ocean at least for some vital functions (i.e., feeding), we used comparisons to fossil marine lizards (e.g., mosasaurids) to discuss some of these unique traits. The new cranial features described for Amblyrhynchus may represent a source of novel morphological characters for use in future phylogenetic analyses of iguanian (or squamate) relationships, which will then serve as the foundation for the exploration of evolutionary patterns and processes that led to the development of such unique adaptations.

Age-related changes in the hyoid bone: An autopsy-based radiological analysis.

Forensic age estimation is a crucial aspect of the biological profile of unidentified cadavers. The utility of age-related changes of hyoid bone fusion in forensic age estimation has not been explored much in the past. These age-related changes can be visualised in both the living and the dead using conventional radiography. These changes can assist medico-legal professionals and forensic anthropologists in the identification of unknown deceased, especially when the cadaver is mutilated or charred or when the other well-established indicators of skeletal and dental maturity are absent. The aims of this study were to evaluate age-related changes in the hyoid bone and to ascertain whether these changes may be utilised for age estimation in forensic examinations. The hyoid bone was carefully dissected using a standard procedure from 75 cadavers during post-mortem examination. The hyoid bone was radiographed, and the bone was replaced in the body cavity before the post-mortem examination was completed. Hyoid bone fusion was studied by using a standard grading method. Spearman's correlation coefficient was calculated between the fusion scores and chronological age to assess their relationship. Box and whisker plots of fusion stage-wise age distribution were constructed to demonstrate the gradual linear relationship between hyoid bone fusion and the chronological age of the study participants. The present study concludes that hyoid bone fusion is an indicator of the chronological age of an individual and can be used in conjunction with other methods of age estimation such as the skeletal and dental age.

Morphological disparity and evolutionary transformations in the primate hyoid apparatus.

The hyoid apparatus plays an integral role in swallowing, respiration, and vocalization in mammals. Most placental mammals have a rod-shaped basihyal connected to the basicranium via both soft tissues and a mobile bony chain-the anterior cornu-whereas anthropoid primates have broad, shield-like or even cup-shaped basihyals suspended from the basicranium by soft tissues only. How the unique anthropoid hyoid morphology evolved is unknown, and hyoid morphology of nonanthropoid primates is poorly documented. Here we use phylogenetic comparative methods and linear morphometrics to address knowledge gaps in hyoid evolution among primates and their euarchontan outgroups. We find that dermopterans have variable reduction of cornu elements. Cynocephalus volans are sexually dimorphic in hyoid morphology. Tupaia and all lemuroids except Daubentonia have a fully ossified anterior cornu connecting a rod-shaped basihyal to the basicranium; this is the ancestral mammalian pattern that is also characteristic of the last common ancestor of Primates. Haplorhines exhibit a reduced anterior cornu, and anthropoids underwent further increase in basihyal aspect ratio values and in relative basihyal volume. Convergent with haplorhines, lorisoid strepsirrhines independently evolved a broad basihyal and reduced anterior cornua. While a reduced anterior cornu is hypothesized to facilitate vocal tract lengthening and lower formant frequencies in some mammals, our results suggest vocalization adaptations alone are unlikely to drive the iterative reduction of anterior cornua within Primates. Our new data on euarchontan hyoid evolution provide an anatomical basis for further exploring the form-function relationships of the hyoid across different behaviors, including vocalization, chewing, and swallowing.