Stylohyoid Research Articles

Variation and Arrangement of the Digastric Muscle in a Chinese Population.

The digastric, a prominent anatomic feature of the head and neck, exhibits clear ethnographic differences in the incidence of variation in its anterior belly (AB) and the relationship of its intermediate tendon (IT) to the stylohyoid (SH). There is a limited amount of information available regarding the digastric in the Chinese population, with most descriptions being individual cases. The present study aims to investigate the variability of AB, elucidate the relationship between IT and SH, and further address the arrangement of individual digastric muscles according to the type of AB and posterior belly (PB) of the digastric, as well as IT, in a Chinese population. Anatomic dissections of the head and neck were carried out bilaterally after student-performed neck dissections during a topographic anatomy course. The types of AB, PB, and IT were recorded to characterize and classify each digastric muscle. The incidence of AB variation was 21.05%. IT type Ⅰ and IT type Ⅱ accounted for 31.25% and 68.75%, respectively. The gross anatomy of the digastric was dominated by the arrangement of AB type I, IT type Ⅱ, and PB type I (63.16%). In addition, 2 rare AB variations were identified. To the best of our knowledge, this is the first report describing individual digastric arrangements and anatomically defining the normal digastric arrangement in the Chinese population. Careful consideration of the variant and anomaly of the digastric is critical for both surgeons and radiologists to provide accurate diagnostic and therapeutic procedures.

Incidental Finding of Double Posterior Belly of Digastric Muscle in Head and Neck Cancer Patient.

The digastric muscles have important roles in swallowing, chewing, speech, and landmark identification during neck dissection. The posterior belly of the digastric muscle (PBDM) is often useful for defining boundaries in surgical neck dissection as it contributes to the carotid, submandibular, and submental triangles. The cadaveric prevalence rate of anatomic variations in the digastrics has been reported to be 31.4% of the population with most occurring in relation to the anterior belly of the digastric muscle (ABDM). Few reports describe variations in the PBDM. While anatomic variants of the digastric muscles do not present with clinical manifestations, they can be mistaken as neck masses and contribute to intraoperative complications. We present a case report of a 73-year-old male with a past medical history significant for Parkinson's Disease, who was incidentally found to have a duplicate PBDM intraoperatively while receiving surgical management of a left buccal squamous cell cancer. Nine months prior to surgery, the patient began experiencing trismus and some mild dysphagia that were eventually worked up to reveal left buccal squamous cell carcinoma (SCC). Prior to this, the patient did not have clinical symptoms demonstrating dysfunction that could be related to or indicative of this anatomical abnormality preceding symptoms related to left buccal SCC growth. The procedure included a wide local excision, left modified radical neck dissection and left submental artery island flap with suprahyoid neck dissection. The superior duplicate PBDM was found to be overlying the stylohyoid muscle. It is important for surgeons operating in the head and neck to be aware of the possibility of this rare variation, and to be conscientious when it is identified so that it does not prohibit or limit a thorough dissection of the neck structures where oncologic clearance is paramount.

Mylohyoid Muscle: Current Understanding for Clinical Management-Part I: Anatomy and Embryology.

The mylohyoid is one of the suprahyoid muscles, along with the geniohyoid, digastric, and stylohyoid muscles. It lies between the anterior belly of the digastric muscle inferiorly and the geniohyoid superiorly. In Part I, the anatomy and embryology of the mylohyoid muscle will be reviewed in preparation for the clinical discussion in Part II.

Mylohyoid Muscle: Current Understanding for Clinical Management Part II: Clinical Anatomy, Radiology, and Surgical/Clinical Relevance.

The mylohyoid is one of the suprahyoid muscles along with the geniohyoid, digastric, and stylohyoid muscles that lies between the anterior belly of the digastric muscle inferiorly and the geniohyoid superiorly. In Part II, the radiology and clinical/surgical importance of the mylohyoid muscle will be discussed.

Ultrasound-guided selective glossopharyngeal nerve block: posterior mandibular ramus approach.

Glossopharyngeal nerve block is a useful interventional technique for pain management of the head and neck. It is performed with landmark techniques or ultrasound guidance. We propose a novel ultrasound-guided glossopharyngeal nerve block technique. This new approach was performed in 3 patients in their twenties and thirties. A needle was inserted deeply under the stylohyoid muscle through the sternocleidomastoid muscle. Subsequently, an ultrasound-guided nerve block was performed with 1 mL of 1% xylocaine. The performance of our technique was evaluated with 2 tests: a cold sensitivity test and a gag reflex test. The effect of the nerve block was observed in the posterior third of the tongue on both sides, the tonsils, and the pharyngeal region. The effect lasted for approximately 1.5 hour. Motor efferent block was not observed. We designated the technique as ultrasound-guided selective glossopharyngeal nerve block: posterior mandibular ramus approach. No complications occurred during the bilateral application. This novel approach can be performed at a very shallow position, compared with conventional methods. There is no damage to tissues other than the muscles, which reduces postoperative complications and patient distress. Although our technique requires further safety assessments and technical refinements, it could represent a simpler alternative to conventional methods in daily clinical practice.

Head posture impacts mammalian hyoid position and suprahyoid muscle length: implication for swallowing biomechanics.

Instantaneous head posture (IHP) can extensively alter resting hyoid position in humans, yet postural effects on resting hyoid position remain poorly documented among mammals in general. Clarifying this relationship is essential for evaluating interspecific variation in hyoid posture across evolution, and understanding its implications for hyolingual soft tissue function and swallowing motor control. Using Didelphis virginiana as a model, we conducted static manipulation experiments to show that head flexion shifts hyoid position rostrally relative to the cranium across different gapes. IHP-induced shifts in hyoid position along the anteroposterior axis are comparable to in vivo hyoid protraction distance during swallowing. IHP also has opposite effects on passive genio- and stylohyoid muscle lengths. High-speed biplanar videoradiography suggests Didelphis consistently swallows at neutral to flexed posture, with stereotyped hyoid kinematics across different head postures. IHP change can affect suprahyoid muscle force production by shifting their positions on the length-tension curve, and redirecting lines of action and the resultant force from supra- and infrahyoid muscles. We hypothesize that demands on muscle performance may constrain the range of swallowing head postures in mammals. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.

Cadaver investigation of the usefulness of the transstyloid diaphragm approach for high-position plaque carotid endarterectomy

ObjectivesPatients sometimes present with high cervical internal carotid artery (ICA) stenosis. This study demonstrates the usefulness of the transstyloid approach to expose the distal ICA by dissection of the styloid diaphragm covering the distal cervical ICA for carotid endarterectomy (CEA). In particular, the possible exposure length achieved by this approach was investigated using cadaveric heads. MethodsThe procedure of the transstyloid diaphragm approach was confirmed in 10 cadaveric heads (20 sides). After the carotid triangle was opened, both the posterior belly of the digastric muscle (PBDM) and the stylohyoid muscle could be divided. Then, the carotid sheath was dissected, and the glossopharyngeal nerve was identified crossing over the distal ICA. The revealed length of the ICA was measured with or without dissection of both the PBDM and the stylohyoid muscle. The specimens were dissected under the surgical microscope. ResultsThe transstyloid diaphragm approach was achieved successfully in all specimens. The revealed lengths of the ICA with and without dissection of the styloid diaphragm were 53.7 ± 5.9 mm and 38.8 ± 2.9 mm (mean ± standard deviation), respectively. Therefore, the revealed length of the distal ICA was 14.9 ± 4.5 mm greater using the transstyloid diaphragm approach compared to the regular CEA approach. ConclusionsMore of the ICA can be revealed by dissection of both the PBDM and the stylohyoid muscle. The transstyloid diaphragm approach might be helpful to reveal the distal ICA in cases of high cervical ICA stenosis.

The stylohyoid muscle revisited: Anatomy and clinical implications

The stylohyoid muscle revisited: Anatomy and clinical implications

Quantitative Prediction of the Location of Carotid Bifurcation and Neurovascular Structures in the Carotid Region: A Cross-Sectional Cadaveric Study.

Introduction The carotid region is encountered in vascular and neurological surgery and carries a potential for vascular and cranial nerve trauma. The carotid bifurcation is an especially important landmark and difficult to predict based on currently established landmarks. This study is a detailed analysis of the carotid region and proposes a novel methodology to predict the height of the bifurcation. Materials and Methods Superficial and deep dissections were performed on the anterior triangle of the neck to expose the carotid region in twenty-one formalin-fixed donor cadavers. Musculoskeletal and neurovascular structures were assessed in relation to the carotid bifurcation and the medial border of the clavicle (MBC). Results The carotid bifurcation occurred, on average, 11.4 mm higher on the left (p < 0.001; 95% CI: 9.28, 13.54). The superior thyroid artery (p < 0.001), facial vein (p < 0.001), and cranial nerve XII (p < 0.001) were all more distal on the left side when measured from the MBC while the angle of the mandible and stylohyoid muscle remained symmetric. Left- and right-sided vascular structures were symmetric when measured from the carotid bifurcation. Conclusions Neurovascular structures within the carotid region are likely to be anatomically superior on the left side while vessels are likely to remain symmetric in relation to the carotid bifurcation. When measured from the MBC, the bifurcation height can be predicted by multiplying the distance between the MBC and mastoid process by 0.65 (right side) or 0.74 (left side). This novel methodological estimation may be easily learned and directly implemented in clinical practice.

Comparative study of the digastric and the stylohyoid muscles between wild boars (Sus scrofa scrofa) and domestic swine (Sus scrofa domesticus): revisiting the gross anatomy.

Considering Suidae Familie as a perfect and viable experimental biomedical model for research applied to human medicine, it has been sought to describe the comparative anatomy of the digastric and the stylohyoid muscles between boars and domestic swine. Heads of Sus scrofa scrofa and Sus scrofa domesticus were dissected. The digastric muscle presented only one muscle belly as anatomical component of a tendinous origin in the jugular process of the occipital bone, and muscle insertion in the midventral edge of the caudal two thirds of the body of the mandible. Thus, its function is fundamentally associated with the lowering and the retracting of the mandible which, by the way, can deliver greater muscle power at lesser energy expense. For the stylohyoid muscle, the tendinous origin was in the laterocaudal edge of the dorsal third of the stylohyoid bone. The muscle insertion - primarily, was in the lateral and caudal edges from the mid third portion up to the ventral extremity of the thyrohyoid bone, and secondarily as a laterolateral aponeurotic blade which would unite, in a bilateral manner, an insertion that was common to the sternohyoid, the geniohyoid, and the mylohyoid muscles in a median ventral region. This morphology were similar to the two specimens studied expanding the information available, which were completely unknown for the suidae until the moment.

Pull-through resection without free-flap reconstruction for lateral wall oropharyngeal cancer.

While transoral robotic surgery (TORS) is widely used for the management of lateral wall oropharyngeal carcinomas (OPC), open surgical techniques are still used in some cases. A pull-through method for open surgical resections of OPC has recently been introduced. We improved on this method by eliminating the need for subsequent free-flap reconstruction. 16 patients with lateral wall OPC underwent pull-through resections. After resection, we used the digastric muscle, stylohyoid muscles, submandibular gland and the surrounding tissues to block the neck and oral cavity and to avoid reconstruction. This novel technique was performed without major complications or morbidities. The average post-operative hospital stay was 14.6±6.1days, and the average duration until initiation of oral intake post-operation was 6.5±2.9days. Oncological outcomes, post-operative course and function were acceptable. Our novel method provides an efficient and less invasive surgical technique than conventional open approaches.

Fibroma of the tendon sheath of the neck

IntroductionFibroma of the tendon sheath (FTS) is a rare benign tumour typically occurring in the extremities, but very rarely involving in the neck. Case reportA 22-year-old male presented with a large painless mass of the right oropharynx. Magnetic resonance imaging (MRI) showed a well-circumscribed 7cm lesion in the right prestyloid space. The lesion was completely removed surgically. Histopathological examination revealed a fibroma of the tendon sheath of the stylohyoid muscle. DiscussionThese tumours generally arise in the extremities of adults. To our knowledge, this is the first reported case of FTS in the neck.

Variations of the digastric muscle and accessory bellies - A study of gross anatomic dissections

Variations of the bellies of the digastric muscle is reported for a long time and is not uncommon. However, there is still not a full consensus about the classifications and many different types of variations. The aim of this study was to examine the variations of the digastric muscle on cadaver dissections and to create a pictorial collection of variations related to present-day by combining with existing knowledge. In the present study, a total of 40 formalin-fixed cadavers and head specimens' digastric muscles were analyzed bilaterally. Previous results were utilized for classification of the variations. Anterior belly, intermediate tendon, and posterior belly variations were evaluated according to unilateral, bilateral and unclassified types. 10 variations were identified in the digastric muscle of 40 cadavers. Thus, five of the variations were unilateral and rest of them were bilateral. Two of the variations were residing in the central area. One accessory muscle bundle was found obliquely residing between the left and right sides of the anterior bellies. Remaining variation was the crossing of the accessory anterior belly of digastric muscle fibers at the central line. Intermediate tendon variation as piercing the stylohyoid muscle was observed in only one case. Posterior belly exhibited no variation. Reporting the abnormalities and variations of the digastric muscle is very important in surgical attempts and evaluation of the lymphadenopathy of the submental area and in the floor of the mouth tumors, numerous clinically significant esthetic surgeries for head and neck surgeons, radiologists and plastic surgeons.

A COMPARISON OF ACTIVATION EFFECTS OF THREE DIFFERENT EXERCISES ON SUPRAHYOID MUSCLES IN HEALTHY SUBJECTS

Purpose: The most crucial airway protection mechanism during swallowing is adequate laryngeal elevation. Suprahyoid muscles are responsible for laryngeal elevation. Our study aimed to compare the effects of three different exercises, Shaker, resistance chin tuck (CTAR) exercise, and chin tuck exercise with theraband, on suprahyoid muscles activity responsible for laryngeal elevation. Methods: Forty-two healthy subjects with a mean age of 27.92±5.02 years (18-40 years), of which 50% were male were included. All individuals were divided into three groups with computerized randomization. Surface Electromyography (EMG) evaluation was performed to determine electrical activity of the suprahyoid muscles (geniohyoid, mylohyoid, anterior belly of digastric, thyrohyoid, stylohyoid muscles) during maximal voluntary isometric contraction and during performing CTAR, Shaker exercise and chin tuck with theraband. Normalized suprahyoid muscle activations were calculated as the recorded maximum electrical activity during exercise (mV)/recorded maximum electrical activity during maximum isometric contraction (mV). Results: A statistically significant difference was found between three groups regarding normalized suprahyoid muscle activation (p<0.001). The difference between the three groups was caused by the difference between CTAR and Shaker (p<0.001) and between CTAR and theraband (p=0.040) in favor of CTAR. No difference was found between Shaker and theraband (p=0.104). Conclusion: Primarily CTAR exercise should be included in rehabilitation to increase the suprahyoid muscle activation. In addition, chin tuck exercise with theraband can also be considered as an alternative to CTAR.

Parapharyngeal Dissection for Papillary Thyroid Cancer

Introduction: Although lymph node metastases are common with papillary thyroid cancer, parapharyngeal and retropharyngeal lymph node metastases are relatively rare. Although small metastatic parapharyngeal lymph nodes (e.g., <1 cm) may be treated with radioactive iodine or observed, larger lymph nodes may require surgical excision. Surgical approaches to the parapharyngeal and retropharyngeal space include transoral and transcervical.Materials and Methods: A 47-year-old female presented with a 2 cm conventional papillary thyroid cancer in the right thyroid lobe with central right lateral neck metastases, as well as a 2.5 cm right parapharyngeal lymph node metastasis extending to the skull base. Surgical technique for transcervical resection of the 2.5 cm parapharyngeal lymph node is illustrated, identifying important anatomical structures.Results: After opening the right neck and removing the right level 2 lymph nodes (not illustrated), the parapharyngeal space is exposed. First, the posterior belly of the digastric and stylohyoid muscles is divided. Next, the hypoglossal nerve is identified and mobilized. Branches of the external carotid artery are then divided and retracted. The sympathetic chain is visualized posterior to the internal carotid artery. The external branch of the superior laryngeal nerve is visualized as it courses posterior to the carotid artery. After gentle retraction of the hypoglossal nerve, superior laryngeal nerve, carotid artery, and sympathetic chain, the parapharyngeal space is exposed with the aforementioned metastatic lymph node. The metastatic lymph node is then freed from the alar fascial and skull base attachments and removed en bloc.Conclusion: To our knowledge, this is the first video demonstration of a transcervical parapharyngeal lymph node resection in the peer-reviewed literature. Transcervical excision of parapharyngeal and retropharyngeal lymph nodes requires a thorough understanding of the anatomy of the neck and parapharyngeal space, along with a stepwise surgical technique to safely expose the parapharyngeal space.No competing financial interests exist.Runtime of video: 8 mins 44 secs

Minimally invasive surgical treatment of a patient with pathological tortuosity of the carotid artery using endoscopic assistance

The study objective is to describe a clinical case of surgical treatment of a patient with pathological distal tortuosity of the left internal carotid artery (ICA) and present a comprehensive description of a proposed surgical technique, as well as compare advantages and disadvantages of the chosen and alternative surgery types.Materials and methods. At the 1st stage, we performed computed angiography and triplex scanning of the main head arteries and modelled operative approach. At the 2nd stage, we mapped the ICA approach, redressing and resection. At the 3rd stage, using endoscopic assistance we separated the ICA along its entire length, found its pathological kink, performed ICA redressing and resection with subsequent reanastomosis with high accuracy and minimal injury.Results. ICAblood flow was 320 ml/min (prior to surgery: 140 ml/min). In the postoperative period, positive dynamics of the patient’s neurological status were observed. Computed angiography and triplex scanning confirmed removal of pathological tortuosity. Compared to the proposed technique, other surgery types (open access) are characterized by high risk of injury of the cranial nerve branches, submandibular and parotid glands, necessity of dissection of the digastric, stylohyoid muscles, subluxation of the mandibula, etc.Conclusion. The method of allocation of hard to reach tortuosities of the carotid artery developed based on previously known endoscopic manipulations on the vessels of the extremities using endoscopic assistance allows to decrease injury during the intervention and achieve maximal technical and clinical effect.

Swallowing Function before and after Subtotal Glossectomy and Reconstruction with a Rectus Abdominis Musculocutaneous Flap: A Case Report

Purpose: Swallowing function was in a patient with tongue cancer that was evaluated with video fluorography before and after subtotal glossectomy and reconstruction with a rectus abdominis muscuocutaneous flap. Materials and Methods: A 41-year-old man underwent subtotal glossectomy and retained the unilateral posterior mylohyoid and unilateral stylohyoid muscles. The structure of the flap was evaluated postoperatively. To assess swallowing function, video fluorography was performed before surgery, 1 month after surgery and 1 year after surgery. Testing involved 1) ability to hold 10 mL of liquid in the oral cavity, 2) epiglottis turnover, 3) the presence of aspiration, 4) hyoid bone movement, and 5) maximum width of the esophageal entrance. Results: The flap was protuberant postoperatively. The patient was able to hold the test diet in the oral cavity before and after surgery. Epiglottis turnover was good before surgery but insufficient after surgery. Aspiration during swallowing was not observed before or after surgery. At rest, the hyoid bone sagged postoperatively, in comparison with preoperatively. Hyoid bone movement and width of the esophageal entrance decreased after surgery; however, they demonstrated gradual recovery. Conclusions: For good postoperative swallowing function after subtotal glossectomy, it is necessary to perform reconstruction with protuberant flap and to retain the suprahyoid muscles as much as possible.

CT血管造影を用いたhigh flow bypassにおけるgraft routeの検討

Because the passage of a graft for a high flow bypass between an anastomosis site of the cervical external carotid artery to the temporal base is made in a blind manner, knowledge of anatomy is essential for a surgeon to perform the high-flow bypass. A radial artery graft provides better long-term patency but shorter available length in comparison to a saphenous vein graft. The radial artery graft, therefore, demands a shorter graft route. The purposes of this study were to confirm a relationship among a graft, surrounding muscles, vessels, and bones on a source image of a computed tomography angiogram (CTASI), and to investigate the shortest graft route. Fourteen patients undergoing high flow bypass for internal carotid artery aneurysms between 2008 and 2015, with a graft demonstrated on a CTASI, were evaluated. The following four types of graft routes including routes 1-3, which were submandibular routes, were classified on CTASIs. Route 1: A graft passes through the medial space to both the posterior belli of the digastric muscle and the stylohyoid muscle. Route 2: A graft goes up to the lateral space to the digastric muscle and turns to the medial space to the stylohyoid muscle. Route 3: A graft goes up to the lateral space to both the digastric muscle and the stylohyoid muscle. Route 4: A subcutaneous route lateral to the mandible. Measurement of the graft length on CTASIs revealed that the route 3 was the shortest among the four routes. The graft in route 3, however, was so close to the external carotid artery between the styloid process and the mandible on a CTASI that a passage tube for the graft could have disturbed the blood flow in the superficial temporal artery, which was used as an assist bypass. In consideration of the limitation of an available graft length, a submandibular route lateral to both the digastric and stylohyoid muscles was the most suitable for high flow bypass using a radial artery graft. Pre-operative observation of the graft routes on CTASIs seems to be useful to prepare for the procedure.

Anomalous course of the external carotid artery.

The course and the branching patterns of the external carotid artery were investigated macroscopically in a total of 550 bodies or 1100 head sides of Japanese subjects, donated for student dissection at Kumamoto University from 1994 to 2014. With the exception of 14 head sides, the external carotid arteries running between the posterior belly of the digastric and stylohyoid muscles were found in 42 (3.87%) out of 1086 head sides. Strictly speaking, they passed between the stylohyoid muscle and the stylohyoid branch of the facial nerve in 23 out of these 42 head sides. In the remaining 19 instances, the stylohyoid branch of the facial nerve was cut and its relationship to the external carotid artery was not clear. The external carotid artery running lateral to the intact stylohyoid branch of the facial nerve, medial to the digastric muscle was not found. The external carotid arteries running lateral to the digastric muscle were found in 4 (0.37%) out of 1086 head sides. As a result, it is proposed that plural, potential courses of the external carotid artery originally exist and that some parts of such potential courses remain as branches of the external carotid artery in the usual instance, while the anomalous courses of the external carotid artery are induced mainly by anastomosis between the muscular branches supplying the wall of the head and neck in contrast to the usual external carotid artery induced mainly by the branches originally supplying the pharynx.

Detailed knowledge of regional anatomy and anatomical variations is fundamental to achieve successful surgical procedure. Although primary objective of neurosurgery is to restore physiological vital functions, remove intracranial mass and prevent further

Detailed knowledge of regional anatomy and anatomical variations is fundamental to achieve successful surgical procedure. Although primary objective of neurosurgery is to restore physiological vital functions, remove intracranial mass and prevent further brain damage, while preserving tissue and organ integrity, the neurosurgeon takes the risk of impairing non-vital functions. Occasionally, as with the hypoglossal nerve, the impairment of anatomical structures found on surgical route is due to their still barely known anatomical relations and variations. In order to provide an anatomically and surgically oriented classification to guide neurosurgical procedures and to ensure the preservation of nerve integrity, the aim of the present study is to detail the course of the 12th cranial nerve (CN) and to establish anatomical landmarks for surgeons. A combination of anatomical dissection of the neck and oral floor and skull base far lateral approach of 6 cadaveric human heads (3 male, 3 female, age 62+4) was performed, on both sides, to explore and follow the entire course of the 12th CN, from its emergence in the preolivary sulcus to the tongue. Skeletal, muscular and vascular relationships were meticulously analyzed and documented during anatomic and surgical dissections. According to our observations, hypoglossal nerve can be divided into five segments. The first two are intracranial, cisternal and intracanalar, and the other three, namely the descending, horizontal and ascending, are extracranial. Intriguingly, we found unreported relations of the nerve that, apart from their anatomical interest, have tremendous significance for surgeons operating on head and neck. Specifically, the intracanalar segment passes through a venous lacuna that, to the best of our knowledge, was never described before as such. This venous structure drains into the jugular bulb and acts as a sheath between the nerve and the osseous wall of the canal. The nerve in the venous sheath bends and it is elastically fixed to the osseous wall of the canal by fibrous bands. Therefore, the venous lacuna guarantees mobility to the nerve, and cushion the nerve from the bone. As for the descending segment, during its course it has very close relationship with the internal jugular vein, the internal carotid artery, the posterior belly of digastric muscle, and the styloid process and muscles inserting on it. The descending segment provides the ansa hypoglossi, branches to muscles inserting on the styloid process and to the sternocleidomastoid muscle. The horizontal segment has relationship with the intermediate digastric tendon, the stylohyoid, hyoglossus and mylohyoid muscles and the submandibular gland. The ascending segment might be very short and sometimes it is absent. The fifth and last segment becomes deeper at the anterior edge of hyoglossus muscle, and terminates into several branches supplying intrinsic and extrinsic musculature of tongue.