Relations of the facial nerve with the retromandibular vein: anatomic study of 132 parotid glands

The Relationship Between the Retromandibular Vein and the Extratemporal Segment of the Facial Nerve: A Prospective Cadaveric Study of 24 Hemifaces

INTRODUCTION

Anatomical preservation and functional integrity of the facial nerve (FN) are the main concerns of parotid surgery. Even though a variety of anatomical landmarks have been proposed and widely utilized, temporal or permanent postoperative FN palsy is still a significant comorbidity of parotid surgery. Therefore, the literature must fully elucidate the consistency of the anatomical relationship between the FN and the retromandibular vein (RMV).

METHODS

We conducted a cadaveric study of 24 hemifaces to map the relationship between the FN and the RMV. Three distinct patterns were identified. Fourteen of the hemifaces were males, and 10 were females. Thirteen cadaveric dissections were performed on the right side and 11 on the left side.

RESULTS

Our study found three distinct patterns and proposed a classification system. Type I (66.7%) is when the nerve lies exclusively lateral to the RMV. Type II (29.2%) is when the FN lies superficial to the RMV, but its mandibular branch lies deep to the anterior branch of the RMV, and type III (4.1%) is when the FN lies exclusively medial to the RMV.

CONCLUSION

The FN and RMV relationship is not constant, and surgeons should be aware of every anatomical variation. Especially in cases where the FN is estimated to lie more in-depth to the level of the RMV, a retrograde approach may be required to avoid a FN injury.

Retromandibular Vein, Digastric Muscle, and Greater Auricular Nerve in Superficial Parotidectomies for Patients with Pleomorphic Adenoma-A Surgical Experience

Retromandibular vein (RMV) and posterior belly of digastric muscle are among the landmarks used to identify facial nerve in parotid surgery. This observational cross-sectional study was done in the Department of ENT &HNS at a tertiary care teaching hospital for a period of 8 years with the aim to aware young otorhinolaryngologist about the relationship of posterior belly of digastric muscle & retromandibular vein with facial nerve and share our experience about preservation of posterior branch of greater auricular nerve. A total of 34 cases of superficial parotidectomies done for pleomorphic adenoma were included in this study. Relationship of facial nerve with retromandibular vein and posterior belly of digastric muscle was noted. Greater auricular nerve was identified, and every attempt was made to preserve its posterior branch. Retromandibular vein was medial to the trunks of facial nerve in 33 (97%) patients. It was lateral to lower division and medial to upper division in one case. Greater auricular nerve was seen to bifurcate into two branches (Anterior and posterior) in 21 (62%) cases while in one case(3%) three branches were seen emerging from main trunk and in another case(3%) first two branches were seen emerging and then anterior branch was further dividing into two. Preservation of posterior branch of greater auricular nerve was possible in 23 (68%) of patients. Posterior belly of digastric muscle was seen as a reliable and constant landmark. Facial nerve was seen superior to upper border of posterior belly of digastric muscle in all cases (100%). No anatomical variation of posterior belly was seen. Retromandibular vein is invariably seen medial to the trunks of facial nerve. Facial nerve is always seen superior to upper border of posterior belly of digastric muscle in almost all cases. Preservation of posterior branch of greater auricular nerve is possible in majority of the cases.

Unusual Relation of Facial Nerve and Retromandibular Vein in Parotid Surgeries: a Case Series

The relation between the facial nerve and the retromandibular vein is of paramount clinical significance during the parotid surgery for the protection of all the facial nerve branches as these two anatomic structures are always in close proximity. However, variations in the relationship of the facial nerve with the retromandibular vein, as presented in this paper complicate parotid surgery and increase the potentiality of unexpected bleeding and injury to the facial nerve injury. This study was conducted in a tertiary care teaching hospital. 4 cases with unusual relation of facial nerve and retromandibular vein in parotid surgeries were studied & included in this study. Out of 70 parotid surgeries which were performed, 4 variations of the retromandibular vein in relation to facial nerve were encountered. With a meticulous dissection the facial nerve branches were separated from the retromandibular vein without causing any injury to the neurovascular structures and functional deficit. Knowledge of normal anatomy of the extra cranial facial nerve and its relation with the retromandibular vein along with the probable anatomical variations leads to a safe parotid surgery.

Reliability of the 'M-Line' in the Prediction of the Facial Nerve Position in Patients with Parotid Neoplasms

Preoperative radiological assessment of parotid tumours represents a crucial step in the planning of a parotidectomy in order to avoid post-operative facial nerve paralysis. The purpose of this study is to determine the reliability of the novel 'M-line' in predicting the facial nerve position and compare it to various radiological methods in the same context. 66 patients whom had underwent parotidectomy for parotid tumours from January 2012 to February 2021 were analyzed. Parotid tumour location were identified using the retromandibular vein, facial nerve line, Conn's arc, Utrecht line and the 'M'-line were compared to the intraoperative location of parotid tumours.The 'M'-line is a novel hypothetical line (drawn between the lateral surface of the mandible to the lateral border of the mastoid process) used to identify the location of the facial nerve radiologically. The 'M-Line' and other methods of radiological assessments were associated with statistical significance in predicting if the parotid tumours were superficial or deep to the facial nerve (p-value < 0.05).The 'M-line' had demonstrated a sensitivity of 73.6% and 92.3% specificity.It had also yielded the highest accuracy (77.3%) in the prediction of the parotid tumour location in relation to the facial nerve. While the radiological lines represented by the Retromandibular vein,facial nerve line,Utrecht line and Conn's arc were statistically significant in predicting the location of the parotid tumour in relation to the facial nerve, the M-line was the most accurate and sensitive predictor in our study.The M-Line is a potentially useful tool to predict the location of the facial nerve in relation to a parotid tumour.

Posterior auricular artery as a novel anatomic landmark for identification of the facial nerve: A clinical study

BACKGROUND

In our previous cadaveric study, we highlighted the posterior auricular artery (PAA) as a potential landmark for early identification of facial nerve (FN) when performing parotidectomy. However, further clinical study is critically needed before this landmark could be applied in clinical practice.

METHODS

For 31 patients enrolled, we tried to identify the FN by the guide of the PAA during parotidectomy. Additionally, the FN function was evaluated during follow-up.

RESULTS

PAA could be exposed in 28 out of 31 (90.3%) patients during parotidectomy. Moreover, the FN trunk could be identified by the guide of the PAA in all these 28 patients with identifiable PAA. Furthermore, no iatrogenic FN damage happened in this study and the transient FN dysfunction rate was 5.7%.

CONCLUSION

The PAA is an ideal landmark for early identification of the FN trunk when performing parotidectomy.

Endonasal access to the lateral poststyloid space: Far lateral extension of an endoscopic endonasal corridor

The styloid process constitutes the posterolateral boundary for an endonasal exposure of the infratemporal fossa. This study aims to explore the feasibility of a far-lateral extension to the lateral poststyloid space via an endonasal corridor. An endonasal dissection was performed on six cadaveric specimens (12 sides). Following an endoscopic endonasal access to the parapharyngeal space, the styloid process and the tympanic portion of the temporal bone were removed to reveal the jugular bulb and the extratemporal facial nerve. Distances from the anterior nasal spine to the relevant landmarks were measured using a surgical navigation device. Through an endonasal corridor, only the anteroinferior aspect of the jugular bulb was exposed. Conversely, the extratemporal facial nerve could be sufficiently exposed, and the deep temporal nerve could be transposed to the stylomastoid foramen. The average horizontal distances from the nasal spine to the posterior tract of V₃ , styloid process, and facial nerve were 79.33 ± 3.41, 97.10 ± 4.74, and 104.77 ± 4.42 mm, respectively. Access to the lateral poststyloid space via an endonasal corridor is feasible, potentially providing an alternative approach to address select lesions extending to this region. The deep temporal nerve has a similar diameter to that of the facial nerve; thus, providing potential reinnervation of the facial nerve.

The external jugular vein axis: a new anatomical landmark for pre-operative prediction of the location of parotid gland tumours

The relationships between parotid tumours and the facial nerve determine duration of surgical procedure and risks involved. As the division of the facial nerve is not visible using standard imaging techniques, other anatomical landmarks are used to determine the pre-operative location of tumours. This retrospective study aimed to evaluate reliability of the 'external jugular vein axis' compared with other landmarks generally used in imaging, such as the retromandibular vein, Conn's arc, the facial nerve line and the Utrecht line. Forty-eight pre-operative imaging exams of patients who underwent parotid benign tumour surgery between 2010 and 2016 were examined. We determined the location of tumour using the five markers. A pre-operative simulation was compared with the description given by the surgeon intraoperatively, in terms of sensitivity and specificity for each marker. External jugular vein axis and retromandibular vein are the most sensitive markers for locating suprafacial tumours (Se = 1). External jugular vein axis and Conn's arc are the most specific markers for locating suprafacial tumours (Spe = 0.92). External jugular vein axis is reproducible and present on all radiological sections, thereby overcoming any anatomical and nomenclature variations. This landmark appears to be the most representative marker of the dividing branches of the facial nerve.

Facial nerve: A review of the anatomical, surgical landmarks and its iatrogenic injuries

Facial nerve iatrogenic injuries are serious and can negatively affect the quality of life of the patients. Due to the properties of the nerve, the complications are devastating involving the aesthetic appearance and the function of the face. Moreover, the multiple branches of the nerve increase the risk of an iatrogenic injury making the detailed knowledge of the anatomical correlations around them critical. In this review, a meticulous analysis was performed including the surgical procedures posing the greater risk of an iatrogenic injury as well as the full description of all the reported anatomical landmarks involving the extracranial course of the facial nerve.

Minimum fascia tumor distance for selection of extracapsular dissection for benign parotid tumors: A preliminary study

OBJECTIVE

There is increasing literature supporting the use of extracapsular dissection (ECD) for the treatment of select superficial lobe parotid tumors, though no objective criteria for selection has been proposed. Prior studies have suggested the minimum distance between the parotideomasseteric fascia and the tumor edge or minimum fascia-tumor distance (MFTD) as a useful measurement for the identification of superficial parotid tumors. The objective of this study is to demonstrate the utility of the minimum fascia-tumor distance in selecting candidates for extracapsular dissection of benign parotid tumors.

METHODS

This is a retrospective case-control study at a tertiary academic otolaryngology clinic. Twenty-three patients with prior surgical excision of benign parotid tumors that underwent surgeon-performed ultrasonography prior to excision of tumor were identified. Ultrasound images were reviewed and the minimum fascia-tumor distance was recorded and categorized by less than 3 mm or as 3 mm or greater. The primary outcome was successful completion of extracapsular dissection versus more extensive resection.

RESULTS

Thirteen patients had a minimum fascia-tumor distance less than 3 mm; eleven of thirteen (84.6%) successfully underwent extracapsular dissection. Ten patients had a minimum fascia-tumor distance of 3 mm or greater; one of ten (10%) successfully underwent extracapsular dissection. A minimum fascia-tumor distance less than 3 mm was sensitive, specific, and accurate in predicting successful ECD at 91.7%, 81.8%, and 87.0% respectively (OR 49.5, 95% CI 3.4-573.2).

CONCLUSION

Minimum fascia-tumor distance may be a useful measurement in identifying candidates for removal of benign parotid tumors with extracapsular dissection.

Retromandibular vein position and course patterns in relation to mandible: anatomical morphologies requiring particular vigilance during sagittal split ramus osteotomy

Major bleeding associated with sagittal split ramus osteotomy (SSRO) involves vessels such as the inferior alveolar, facial, and maxillary arteries and veins, and the retromandibular vein (RMV). The present study aimed to clarify and classify the three-dimensional variations in RMV position and course direction in relation to the mandible. Specimens comprised a total of 15 scientific cadavers, and the relationship between RMV and the mandible lateral and posterior views was observed. We identified 3 patterns on the lateral view, the mean distance between the RMV and the posterior border of the ramus was 3.9 mm at the height of the lingula. A total of five course patterns were identified on the posterior view. In no course pattern, the RMV inferior to the lingula was lateral to its position superior to the lingual. The present findings suggest that it may be possible to predict correlations with intraoperative bleeding risk. Further study is planned using contrast computed tomography in patients with jaw deformity for skeletal classification.

Feasibility of Using Posterior Auricular Artery as Landmark for Identification of Facial Nerve Trunk in Parotid Surgery: A Cadaver Study

INTRODUCTION

Despite good surgical knowledge of the anatomy of parotid gland and meticulous surgical technique, the incidence of facial palsy in parotid surgeries is up to 26.7% transient and 1.7% complete facial palsy(1). The risk of facial palsy increases further in malignant and revision cases.

METHOD

Superficial parotidectomy was done in 14 cadaveric hemi faces in 10 cadavers. Posterior auricular artery and its stylomastoid branch was dissected and facial nerve trunk was identified in all cases. The relationship of posterior auricular artery along with its stylomastoid branch with the facial nerve trunk was studied and recorded.

RESULT

Posterior auricular artery was found running inferior to the facial nerve trunk in 12 cadaveric dissection while the posterior auricular artery was found crossing below the main trunk of facial in 2 cadaver dissection. The average distance between PAA and facial nerve trunk was 7 mm (2-14 mm) Stylomastoid artery was found arising from Posterior auricular artery in 12 of 14 and it was found running medial to the facial nerve trunk in all the 8 cadavers.

CONCLUSION

Post auricular artery can be used as another landmark for identification of the main trunk of facial nerve in parotid surgeries.

Identification of the intraparotid facial nerve on MRI: a systematic review and meta-analysis

OBJECTIVES

Accurate preoperative localization of the intraparotid facial nerve (IFN) on MRI could reduce intraoperative injury. This study aimed to assess the detection rate of the IFN and its branches on MRI.

METHODS

PubMed-MEDLINE and Embase databases were searched for articles published up to October 2019. The inclusion criteria were (a) adults, (b) MRI-based identification of IFN by radiologists, (c) original articles, and (d) detailed results to assess the proportion of visible IFN. Two radiologists reviewed the original articles. The Quality Assessment of Diagnostic Accuracy Studies-2 tool was used to determine the quality of the selected studies. The DerSimonian-Laird random effects model was utilized to calculate the pooled estimates. Between-studies heterogeneity was evaluated using the chi-squared statistic test and Higgins' inconsistency index (I²). A subgroup meta-regression was performed to explore the factors causing study heterogeneity.

RESULTS

Nine original articles with 209 subjects were included. MRI reported a high pooled detection rate of 99.8% (95% CI, 98.4-100%) for the main trunk of the IFN. The pooled rates for the temporofacial and cervicofacial branches were 90.4% (95% CI, 84.1-96.7%) and 96.3% (95% CI, 96.1-99.5%), respectively. Heterogeneity was detected only in the temporofacial branch (I² = 83%) as a result of both slice thickness and the use of steady-state sequences with diffusion-weighted imaging (DWI) implementation.

CONCLUSIONS

MRI showed an overall high detection rate of the IFN and its branches. Furthermore, an increased identification was observed in studies that used a slice thickness of < 1 mm and steady-state sequences with DWI implementation.

KEY POINTS

• MRI showed an overall high detection rate of the intraparotid facial nerve and its branches. • Higher detection rate was observed in studies that used a slice thickness of < 1 mm and steady-state sequences with diffusion-weighted imaging.

Anatomical Characteristics of Facial Nerve Trunk in Vietnamese Adult Cadavers

BACKGROUND:

In medical literature, there are few studies provided a precise and detailed description of the facial nerve rami and its branches.

AIM:

Identify several practical anatomic landmarks related to the facial nerve main trunk and its rami.

METHODS:

A descriptive study, 30 cadavers in the anatomy department of UPNT from October 2012 to April 2015.

RESULTS:

The average distance from the mandibular angle to the division of the facial nerve is 40.8 mm, and is 86.6% from range 36 – 50 mm. There is 86.7% case in which the facial nerve is in the lateral of the retromandibular vein, and there is a significant difference about both sides. Eighty percent of the case has the superior and inferior ramus in the lateral to the retromandibular vein. There are 2 cases in which the superior ramus makes the circle of the vein. Eighty percent of the facial nerve is in the lateral to the external carotid artery.

CONCLUSION:

The distance from the mandibular to the division of the facial nerve is longer. The relationship between the superior/inferior ramus and the retromandibular vein maybe not the same in both sides. In some cases, it makes the circle of the vein to cause some complication in the parotid gland surgery.

An Unusual Position of Retromandibular Vein in Relation to Facial Nerve: A Rare Case Report

Knowledge of different anatomical structures is very important in parotid surgery to preserve facial nerve. Retromandibular vein is one of the landmarks used to identify facial nerve. So, the relation of the vein with facial nerve is very important in parotid surgery. The typical position of RMV is deep to facial nerve in almost 88% of cases reported in various literatures. Here, we present an unusual position of RMV found during parotid surgery for pleomorphic adenoma.

Variations of Retromandibular Vein and Its Relation to Facial Nerve Within Parotid Gland

Maxillary vein and superficial temporal vein unite to form the retromandibular vein in the parotid gland. The facial nerve lies lateral to external carotid artery and retromandibular vein. Identifying and preserving the facial nerve is the prime motto during parotidectomy. So the variations of facial nerve and the retromandibular vein should be known so as to avoid injury to both. The variations we encountered during parotid surgery will be helpful in avoiding unexpected bleeding and injury to facial nerve.

Posterior auricular artery as a novel anatomic landmark for identification of the facial nerve: A cadaveric study

BACKGROUND

Despite preservation techniques, performing a parotidectomy carries a transient facial nerve dysfunction rate in up to 65% of cases and a permanent facial nerve weakness rate of 4%-7%.

METHODS

The lateral aspect of the face and neck was exposed in 5 cadaveric heads (10 sides). The relationship of the posterior auricular artery (PAA) and the facial nerve was studied and recorded and descriptive measurements were taken.

RESULTS

In all specimens, the facial nerve trunk crossed the PAA inferior to the stylomastoid foramen and could be identified precisely by tracing the PAA proximally. The distance from the cross point of the PAA and the facial nerve to the external meatal cartilage was 5.2 ± 0.2 mm.

CONCLUSION

The PAA represents a potential new anatomic landmark for facial nerve identification at the main trunk.

Anatomic variation of the relation between the facial nerve and the retromandibular vein during superficial parotidectomy: A rare case report

•

The facial nerve (FN) and the retromandibular vein (RMV) are anatomical structures in close proximity. Anatomic variations of their relationship complicate parotid surgery and increase the potentiality of nerve injury or bleeding.

•

The true prevalence of such kind of variations seems to be underestimated, since the literature is restricted.

•

Novel variations of the relationship of the FN with the RMV are probable. Therefore, surgeons’ knowledge and perpetual awareness are fundamental and essential in order to perform safe parotid surgery.

Introduction

Identification and preservation of the facial nerve (FN) is a major challenge when performing parotidectomy. Anatomic variations of the relation between the FN and the retromandibular vein (RMV) pose a high risk of nerve injury and bleeding during the operation.

Presentation of case

An unusual anatomic variation of the relation between the FN and the RMV was unexpectedly detected during superficial parotidectomy. The operation was uneventful. A meticulous review of the recent literature was conducted as well.

Discussion

Variations of the relation between the FN and the RMV are mainly identified during the operation, since when performing parotidectomy, surgeons typically detect all the FN branches by locating the RMV. Such kind of variations, are not as rare as considered and their presence complicates parotid surgery and increases the potentiality of nerve injury and hemorrhage.

Conclusion

Surgeons’ deep knowledge and perpetual awareness concerning the probable anatomic variations of the relation between the FN and the RMV combined with detailed exposure of the operative field and of the relationship between these adjacent anatomical structures lead to safe parotid surgery.

An unusual position of retromandibular vein: a surgical challenge in parotid surgeries

A 44-year-old man presented with swelling in the left parotid region. The swelling was firm and Fine Needle Aspiration Cytology report proved pleomorphic adenoma. In the CT scan, the tumour was confined to the superficial lobe of parotid. So, left superficial parotidectomy was planned. Modified Wilson Blair's incision was used. On course of identifying the facial nerve, a large calibre vein was identified running vertically through the parotid substance. Assuming it as retromandibular vein, further dissection was carried out more meticulously. Marginal mandibularbranch of facial nerve was identified near the angle of mandible and retrograde dissection showed the cervicofacial division running medial to retromandibular vein with the main facial nerve trunk lying unusually medial and posterior to it. Adding to it, the temporofacial division was found 'forked' between the branches of retromandibular vein. These variations in head and neck venous channels are not that rare as we believe. All these variations have an embryological basis. Therefore, knowledge and understanding of this complex anatomy will help us preventing devastating complications like bleeding and facial nerve injury in such cases.

Relations of Facial Nerve With Retromandibular Vein in Human Fetuses

The relationship of facial nerve (FN) and its branches with the retromandibular vein (RMV) has been described in adults, whereas there is no data in the literature regarding this relationship in fetuses. The study was conducted to evaluate the anatomic relationships of these structures on 61 hemi-faces of fetuses with a mean age of 26.5 ± 4.9 weeks with no visible facial abnormalities. The FN trunk was identified at its emergence at the stylomastoid foramen. It was traced till its ramification within the parotid gland. In 46 sides, FN trunk ramified before crossing RMV and ran lateral to it, while in 8 sides FN trunk ramified on the lateral aspect of the RMV. In 3 sides, FN trunk ramified after crossing the RMV at its medial aspect. In only 1 side, FN trunk trifurcated as superior, middle, and inferior divisions and RMV lied anterior to FN trunk, lateral to superior division, medial to middle and inferior divisions. In 2 sides, FN trunk bifurcated as superior and inferior divisions. Retromandibular vein was located anterior to FN trunk, medial to superior division, lateral to inferior division in both of them. In 1 side, RMV ran medial to almost all branches, except the cervical branch of FN. Variability in the relationship of FN and RMV in fetuses as presented in this study is thought to be crucial in surgical procedures particularly in early childhood.

The Utility of In-Office Ultrasound in the Diagnosis of Parotid Lesions

Objective

To determine whether the use of in-office ultrasound (US) by a head and neck surgeon is a useful adjunct to clinical assessment of parotid lesions and decrease the need of additional imaging, such as magnetic resonance imaging (MRI) or computed tomography (CT).

Study Design

Case series with chart review.

Setting

Tertiary care academic center.

Subjects

Seventy patients presenting with a parotid lesion who obtained an in-office US and ultrasound-guided fine-needle aspiration (USGFNA) from a head and neck surgeon from 2006 to 2015.

Methods

US images were retrospectively reviewed for 70 patients and characterized by a radiologist and a head and neck surgeon.

Results

Of the 70 patients, 6 had US characteristics that demonstrated a statistically significant association with a benign/malignant diagnosis: depth from surface; irregular borders; presence of calcifications, which included either micro- or macro-calcifications; posterior echogenicity enhancement; irregular shape; and homogeneous/heterogeneous echotexture. Imaging was performed prior to referral in 25 cases (35.7%); of those, 17 (68%) were for superficial, small (<2 cm) tumors where prereferral imaging studies did not provide additional information to that obtained with US. Of the 55 patients without MRI or CT performed prior to referral, MRI or positron emission tomography–CT scan was obtained in only 4 patients (7.3%) in cases involving recurrent parotid lesions, large tumors, or workup of a malignant neoplasm.

Conclusions

Several US characteristics individually assist in lesion characterization. In-office US and USGFNA are an appropriate first-line modality in the assessment of parotid lesions, can allow for immediate parotid lesion assessment, and can decrease the need for additional imaging.

Facial Nerve Anomaly in a Patient With a Parotid Tumor: A Case Report

The branching pattern of the facial nerve varies among individuals. These variations increase the risk of facial nerve injury during parotid surgery. We report a new variation of the facial nerve and an unusual relationship with the retromandibular vein during parotid surgery.Clinicians should recognize this facial anomaly and the unusual relationship with the retromandibular vein to avoid injuring the facial nerve during parotid surgery.

The styloauricular muscle: clinical relevance and literature review of this rare muscle

PURPOSE

In humans, the styloauricularis is a rare muscle extending from the tragal cartilage of the auricle to the styloid process. When it contracts, by bearing on the styloid process, it increases the cephalo-auricular angle. It can be a landmark for the facial nerve. We report a case with bilateral presence of the styloauricularis.

METHODS

Bilateral presence of the styloauricularis was discovered during routine dissection of the head and neck.

RESULTS

In the presented case, styloauricularis muscles arose from the cartilage of the external acoustic meatus on both sides of the head, crossing halfway along the facial nerve trunk and inserting the styloid process. Both muscles were vascularized by a branch of the posterior auricular artery, and innervated by the facial nerve.

CONCLUSIONS

The ventral auricular muscle, formed by the auricular parotid and the styloauricular muscles, is a muscle that lowers and abducts the auricle in animals. There is generally considered to be no equivalent for these muscles in humans, however, this bilateral case reveals evidence to the contrary. There is a dearth of scientific literature about the styloauricularis. The study of this muscle demonstrated the usefulness of comparative anatomy in understanding its action in increasing the cephalo-auricular angle.