A recurrent variant branch of the inferior alveolar nerve: Is it unique?

The only named branch of the inferior alveolar nerve (IAN) before it enters the mandibular foramen is the mylohyoid nerve. However, several variations have been reported in the literature. In this study, a recurrent variant branch of the IAN arising just below the origin of the mylohyoid nerve was investigated in adult Indian cadavers allotted for dissection to the first year dental students of Government Dental College, Ahmedabad (India). The dissection was performed by the lateral approach to the infratemporal fossa. The nerve was found in 12 of 35 sides (34.3%) and 8 of 18 cadavers (44.4%). Thus, in our study it was not a rare variation of the IAN, where in most cases it innervated the lateral pterygoid muscle. In some cases, it terminated in the lateral pterygoid muscle. In others, it penetrated the muscle to join the anterior or posterior division of the mandibular nerve or its branches; thus, the variant nerve in such cases might be regarded as an additional root of the IAN. Because the concerned primordia of the nerves and muscles migrate extensively during development and growth, alternative routes of migration may bring about variants like the one under study. The variant appeared to be unique in some of its features. It may be a source of neuropathic and referred pain. Failure of the conventional inferior alveolar nerve block anesthesia and the peripheral neurectomy used for the treatment of trigeminal neuralgia may be partly due to the presence of this variation.     

Spatial relationships between masticatory muscles and their innervating nerves in man with special reference to the medial pterygoid muscle and its accessory muscle bundle

The relationships between the positional arrangement of the surrounding and innervating nerves of the muscles supplied by the mandibular nerve, in particular those medial to the main trunk of the nerve, were examined in 24 head halves from 12 Japanese cadavers by dissection from the inside after removal of the bony elements except for the mandible. In ten sides of five heads, the lingual nerve pierced the medial pterygoid muscle, and the bundle lateral to the nerve was found to be separated as an accessory muscle bundle. The accessory bundle was frequently attached to the mylohyoid muscle. In addition, the inferior alveolar nerve and the lingual nerve frequently communicated, and in four specimens a branch from the lingual nerve entered the mylohyoid to communicate with the proper nerve. The innervation pattern indicated that the medial pterygoid muscle consists of the anteromedial and the posterolateral main parts, and sometimes has an accessory bundle. Based on the present findings and the previous studies of the positional relationships between the muscles and nerves by our research group, we propose that the muscles innervated by the mandibular nerve could be classified as an inner group (the lateral pterygoid) and an outer group (the other muscles). A possible scheme of the positional relationships between the muscles and nerves is presented.     

Supernumerary muscle bundles in the submental triangle: their positional relationships according to innervation

The positional relationships between the supernumerary muscle bundles within the submental triangle and their innervating branches from the mylohyoid nerve were investigated. Ten heads of Japanese cadavers that showed aberrant muscle bundles within the submental triangle were examined. Three additional heads without such aberrant bundles were used for comparison. All cadavers were fixed with 8% formalin and preserved in 30% ethanol. After the examination of the origin and insertion of the muscles, the bony elements were removed, and then their innervating branches from the mylohyoid nerve were examined in detail under a binocular microscope. In 11 head-halves of six cadavers unilateral supernumerary bundles were found. Right and left mylohyoid nerves gave off branches that crossed the inner surface of the bundles of each respective side. Supernumerary bundles ran across the median line in two heads. In one head, the twigs from the mylohyoid nerve of the same side as the mandibular origin entered the inner surface of the bundles. The other head received double innervation from right and left nerves. Three heads showed supernumerary bundles that attached to the mandible or the hyoid bone at one end and joined the mylohyoid muscle at the other end. The branches from the mylohyoid nerve of the digastric side entered the inner surface of the bundles, and those of the mylohyoid side entered their outer surface. After giving off branches to the muscles, the mylohyoid nerve continued as a cutaneous nerve of the submental region. Based on the innervation patterns of the aberrant bundles within the submental triangle, it was suggested that these bundles result from the combination of the remnants of the primordia of the mylohyoid muscle and the anterior belly of the digastric.     

Topographic anatomy of the lingual nerve and variations in communication pattern of the mandibular nerve branches

We made a thorough observation of the morphology and course of the lingual nerve (LN) and inferior alveolar nerve (IAN) to clarify their topographical relationships in the infratemporal fossa and in the paralingual area. Thirty-two Korean hemi-sectioned heads were dissected macroscopically and microscopically from a clinical viewpoint. On the 32 tracings on the radiograph, the average distance between the retromolar portion and the LN was 7.8 mm, and no case was found where the LN ran above the alveolar crest as passing along the mandibular lingual plate. The bifurcation of the LN and IAN was located around the mandibular notch, inferior to the otic ganglion in 66% of the cases, and a plexiform branching pattern of the mandibular nerve was observed in only two cases. The bifurcation spot of the LN and IAN was located 14.3 mm inferior to the foramen ovale and 16.5 mm superior to the tip of hamulus. Collateral nerve twigs from the LN to the retromolar area were observed in 26 cases (81.2%), with an average of one nerve twig. We observed four types of variations in terms of communication pattern. In four specimens, the mylohyoid nerve passed through the mylohyoid muscle and connected with the LN. In other four specimens, the IAN communicated with the auriculotemporal nerve. We also observed another type of variational communication between the IAN and the nerve to the lateral pterygoid (LPt); this was observed in only one specimen, and it could be predicted that motor innervation from the nerve to the LPt was transmitted via the mental nerve to the depressor anguli oris. Another type was observed where the IAN divided into two branches with the posterior branch being partially entrapped by the LPt muscle fibers.     

Masticatory Muscles and Branches of Mandibular Nerve: Positional Relationships Between Various Muscle Bundles and Their Innervating Branches

The masticatory muscles, which are composed of four main muscles, are innervated by branches of only one of the cranial nerves, the mandibular nerve. This muscle group has a variety of very complex functions. We have investigated the origins and insertions of the masticatory muscles and the adjacent bundles of the main muscles, and closely examined the positional relationships between the muscle bundles and innervating branches. According to the findings of the nerve branching patterns, the masticatory muscles can be classified into two groups: the inner group consisting of the lateral pterygoid muscle, and the outer group consisting of the other muscles and adjacent muscle bundles. Further, the outer muscle group is sub-divided into the three other main muscles (the masseter, the temporalis, and the medial pterygoid muscle) and the adjacent various transitional muscle bundles. Anat Rec, 302:609–619, 2019. © 2018 Wiley Periodicals, Inc.     

Functional morphology of the maxillo-mandibular apparatus of the mini-Lewe minipig. 7. Intramuscular nerve ramification model of the masseter muscle of juvenile animals

The ramification patterns are basically the same at all ages. The existing patterns of intramuscular innervation change gradually only by increasing ramification. The masseter and zygomaticomandibularis muscles are innervated jointly by branches of the massetericus nerve. The medial pterygoid muscle is supplied by 2 branches. In 3 d old animals the lateral pterygoid muscle is supplied by a single branch, but 2 branches are already present in animals aged 2 months. The temporal muscle is innervated by 5 branches.     

Functional anatomy of the mandibular nerve: consequences of nerve injury and entrapment

Various anatomic structures including bone, muscle, or fibrous bands may entrap and potentially compress branches of the mandibular nerve (MN). The infratemporal fossa is a common location for MN compression and one of the most difficult regions of the skull to access surgically. Other potential sites for entrapment of the MN and its branches include, a totally or partially ossified pterygospinous or pterygoalar ligament, a large lamina of the lateral plate of the pterygoid process, the medial fibers of the lower belly of the lateral pterygoid muscle and the inner fibers of the medial pterygoid muscle. The clinical consequences of MN entrapment are dependent upon which branches are compressed. Compression of the MN motor branches can lead to paresis or weakness in the innervated muscles, whereas compression of the sensory branches can provoke neuralgia or paresthesia. Compression of one of the major branches of the MN, the lingual nerve (LN), is associated with numbness, hypoesthesia, or even anesthesia of the tongue, loss of taste in the anterior two thirds of the tongue, anesthesia of the lingual gums, pain, and speech articulation disorders. The aim of this article is to review, the anatomy of the MN and its major branches with relation to their vulnerability to entrapment. Because the LN expresses an increased vulnerability to entrapment neuropathies as a result of its anatomical location, frequent variations, as well as from irregular osseous, fibrous, or muscular irregularities in the region of the infratemporal fossa, particular emphasis is placed on the LN.     

Double innervation of the anterior belly of the digastric muscle

We came across a very rare case in which the anterior belly of the digastric muscle was innervated by the twigs of the facial nerve in addition to those of the mylohyoid nerve. The anomaly was discovered in the cadaver of an 84-year-old Japanese male bequeathed for a training seminar in gross anatomy at Kumamoto University in 2003. One twig issued from the marginal mandibular branch of the facial nerve and entered the central region of the anterior belly of the digastric muscle on the lower surface. The other twig issued from the stylohyoid branch of the facial nerve, descended along the lateral margin of the stylohyoid muscle and entered the anterior belly of the digastric muscle on the lower surface near the intermediate tendon. The twig from the marginal mandibular branch was distributed to the shallow (lower) and central region near the medial margin of the anterior belly. The twig from the stylohyoid branch was distributed to the shallow and lateral region of the anterior belly. These two twigs communicated with the mylohyoid nerve at several peripheral parts. Textbooks on general anatomy make mention of only one nerve, the mylohyoid, supplying the anterior belly of the digastric muscle. However, the present case manifests that the anterior belly receiving twigs from the mylohyoid and facial nerves is formed with the second brachial component as well as the first.     

Derivation of the anterior belly of the digastric muscle receiving twigs from the mylohyoid and facial nerves

The anterior belly of the digastric muscle is usually supplied by the mylohyoid nerve, and in general anatomy textbooks, the anterior belly is invariably described as receiving no other nerve except the mylohyoid nerve. In fact, however, it is sometimes supplied by a branch of the facial nerve in addition to the mylohyoid nerve. Such cases were found in 8 bodies or 9 head sides among 539 bodies or 1078 head sides of Japanese subjects. Those nine cases were investigated in detail and it was clarified that they had the following three characteristics in common: (1) the twig originating from the facial nerve appears as the twig of the stylohyoid branch in most cases, (2) the twig from the facial nerve enters the anterior belly on its lower (shallow) surface and the twig of the mylohyoid nerve on its upper (deep) surface, (3) the twig of the mylohyoid nerve is distributed to the deep region and the twig of the stylohyoid branch is distributed to the shallow region of the anterior belly. From these results, it was concluded that the anterior belly, receiving the twigs of the mylohyoid and facial nerves, had been formed by secondarily combining the most ventral and rostral part of the primordium of the stylohyoid muscle in the second branchial arch with the caudal part of the primordium of the anterior belly in the first branchial arch.     

Nerve communication between the glossopharyngeal nerve,external carotid plexus and the superficial cervical ansa: human autopsy case

The authors encountered a very rare human autopsy case in which the supernumerary branch of the glossopharyngeal nerve and a nerve branch arising from the external carotid plexus communicated with the superficial cervical ansa. This anomaly was observed on the left side of a 71-year-old male cadaver during the gross anatomical seminar at Niigata University in 2004. The nerve fascicle and fiber analyses indicated that the supernumerary branch of the glossopharyngeal nerve separated cranial to the branches to the pharyngeal constrictor muscles, carotid sinus and stylopharyngeal muscle and sent the nerve fibers to the muscular branches to the platysma and the cutaneous branches to the cervical region. Additionally, it was shown that the branch arising from the external carotid plexus sent the nerve fibers to the cutaneous branch to the cervical region. Although the external carotid plexus is primarily postganglionic sympathetic fibers originating from the superior cervical ganglion, the vagus and glossopharyngeal nerves gave off branches connecting to the plexus, and therefore it was not possible to determine the origins of this branch of the external carotid plexus. The present nerve fascicle analysis demonstrates that the supernumerary branch of the glossopharyngeal nerve, which innervated the platysma, did not share any nerve components with the branches to the pharyngeal constrictor muscles, carotid sinus and stylopharyngeal muscle, suggesting that this supernumerary branch may be categorized into the different group from these well-known branches.     

The distribution of the radial and musculocutaneous nerves in the brachialis muscle

Few have examined the distribution of the radial nerve branch to brachialis, generally believed to be motor, within the muscle. We examined the right brachialis muscles of six dissecting room cadavers and found that four received a supply from the radial nerve. The radial nerve branch(es) supplied the inferolateral region of the muscle and was overlapped proximodistally and mediolaterally by the intramuscular branches of the musculocutaneous nerve, which lay on a more superficial plane. The results have implications for the anterolateral approach to the humerus for orthopedic surgery. Anterior splitting of the muscle will almost certainly damage the most lateral branches of the musculocutaneous nerve.     

Dual innervation of the brachialis muscle

A study of the innervation of the brachialis muscle was carried out on 45 male and 31 female Thai cadavers between the ages of 15 and 92 years (mean = 59 years). The dissections revealed that all brachialis muscles received innervation from the musculocutaneous nerve and that 81.6% were also innervated by a branch from the radial nerve. Among the brachialis muscles with a dual nerve supply, two patterns of branching from the radial nerve were observed: in one pattern the branch to the brachialis had a descending course (58%) and in the other pattern the nerve ascended or recurred (42%) to innervate the muscle. The radial nerve branch penetrated the inferolateral part of the brachialis muscle in 83% of cases (103/124) and its middle third in 17% of specimens (21/124). The basis for the dual innervation may result from fusion of two different embryonic muscular primordia: the ventral (flexor) and the dorsal (extensor) muscle masses. In contrast to a brachialis muscle innervated by the musculocutaneous nerve only, a muscle with dual innervation may be spared significant denervation by an anterior approach to the humerus through a longitudinally bisected muscle. In a dually innervated muscle, however, separation of the brachialis and brachioradialis muscles during surgery may put the radial nerve branch to the brachialis at risk.     

人膈肌内神经分支分布

目的：探讨人膈的神经支配和肌内神经分支分布特点。方法：改良Sihler’s肌内神经分支染色法。结果：(1)一侧膈神经入肌后一般分为3—4支(3支型4例,4支型2例),1支(前支)向前内侧走行,支配胸部,1～2支(前外侧支)向外侧走行,支配肋部,最后1支(后支)最粗大,向后下走行,分为后外侧支和后脚支,分别支配膈中心腱外侧叶后外侧的肋部和腰部,各级神经的分支在肌束中部密集排列成神经丛。(2)6例标本均未发现左侧或右侧膈神经越过中线至对侧。(3)2例带肋间肌的标本肉眼未见有肋间神经分支进入膈。结论：(1)左、右膈神经分布于膈,未见左右侧膈神经重叠支配和优势支配。(2)膈神经的终末分支在肌束中部密集排列形成似“肾形”的神经丛带。     

腹外斜肌的神经入肌点定位与肌内神经分布研究

目的　对人腹外斜肌的神经入肌点定位和肌内神经染色观察，为其临床应用提供形态学资料。 方法　成尸11具定位神经入肌点和5具行Sihler’s 肌内神经染色。 结果　腹外斜肌受下8对肋间神经外侧肌支支配，各个肌齿的神经入肌点距离相应肌齿起端中点(1.54±0.33)cm，位于锁骨中线与第5肋下缘的交界处至腋后线与第11肋下缘交界处的连线上。Sihler’s染色显示支配腹外斜肌的肋间神经外侧肌支入肌后分出小分支分布到各肌齿的起端1/3，然后约在各肌齿的近、中1/3交界处分出2支二级神经分支，即上支与下支，它们分出小分支分布到各肌齿的中间1/3，相邻两个肌齿的上支与下支在各肌齿中远部形成“U”形吻合，从“U”形吻合弓上分出小分支分布到各肌齿的止端1/3。在腹外斜肌上半部，各肌齿的神经分支分布到相应的肌齿，但在腹外斜肌下半部，上一肌齿的远侧下份是由下一肌齿的神经分支(上支)分布。 结论　①为临床上腹壁局部麻醉和术后切口疼痛的神经阻滞提供指导意义；②腹外斜肌中远部从上至下形成“波浪形”的神经分支密集区；③腹部手术切口建议不要超过四个肌齿。     

Surgical anatomy of the radial nerve branches to triceps muscle

The objectives of the study are to demonstrate the innervation patterns of the triceps muscles and the most suitable branch of the radial nerve for nerve transfer to restore the motor function of the deltoid muscle in patients with complete C5–C6 root injury. Seventy‐nine arms (40 left arms and 39 right arms) from 46 embalmed cadavers (24 male and 22 female) were included in the study. The nerves to the triceps were dissected from the triceps muscles (long head, lateral head, and medial head). The lengths of the branches were measured from the main trunk. The distance from the inferior margin of the teres major muscle to the origin of the nerve to the long head, lateral head, and medial head of the triceps were recorded as well. The first branch was the nerve to the long head of the triceps in 79 arms (100%). The second branch was the nerve to the upper medial head in 30 arms (38%), nerve to the medial head in 8 arms (10.1%), nerve to the upper lateral head in 35 arms (44.3%) and nerve to the lateral head in 6 arms (7.6%). The patterns of branches to the triceps were classified according to our dissections. The nerve to the long head of the triceps was constant as the first branch of the nerve to the triceps branch of the radial nerve in the vicinity of the inferior margin of the teres major muscle. Clin. Anat. 2013. © 2012 Wiley Periodicals, Inc.     

Ia类传入神经纤维在腓肠肌神经终支的分布

目的：探讨Ｉａ类传入神经纤维在腓肠肌神经终支内的分布。方法：对人腓肠肌内侧头神经肌支的终支进行Ｋａｒｎｏｖｓｋｙ乙酰胆碱脂酶组织化学染色。结果：人腓肠肌内侧头神经三终支内,大直径有髓神经纤维分为酶反应阴性和阳性两类。三终支内所含酶应阴性的大直径有髓神经纤维抽样结果显示,三支间均有显著性差异,结论：人腓肠肌内侧头神经终支内各类纤维在横断面上呈散在分布,未见集中趋势,在腓肠肌内侧头神经肌支的三终支内,     

Innervation of the medial epicondylar muscles: an anatomic study in 50 cases

The median nerve is classically distributed to the medial epicondylar muscles by two branches (superior and inferior) for the pronator teres muscle, a common trunk for the flexor carpi radialis and palmaris longus muscles, and a branch for the flexor digitorum superficialis muscle. The 50 dissections were made by two workers on 30 upper limbs of formolized cadavers and 20 limbs from fresh-frozen cadavers. The innervation of the pronator teres m. was classical in only 26% of cases, and the “normal” pattern for the flexor carpi radialis and palmaris longus mm. was found in only 40% of cases. The innervation of the flexor digitorum superficialis m. was the least subject to variations, a single branch being observed in 68% of cases. We found a solitary medio-ulnar anastomosis of Martin-Gruber to the flexor carpi ulnaris muscle. This study confirmed the great variability of the branches of the median nerve at the elbow, and the importance of identifying them in surgical procedures for transposition of the medial epicondyle.     

Ramification pattern of the deep branch of the lateral plantar nerve in the human foot

To understand how the oblique and transverse heads of the adductor hallucis muscle of the human foot are phylogenitically and ontogenetically developed, it is essential to know nerve supplies of these two heads of the muscle. In the present study, we dissected seven feet of five Japanese cadavers in detail to clarify the ramification patterns of the deep branch of the lateral plantar nerve by peeling off its epineurium (the nerve fascicle analysis method). We found that the muscular branch to the oblique head of the adductor hallucis muscle directly separated from nerve fascicles constituting the deep branch of the lateral plantar nerve, whereas the muscular branch to the transverse head arose in common with branches which innervated other intrinsic muscles of the foot, i.e., the 2nd and 3rd lumbrical muscles and the 1st and 2nd dorsal interossei muscles. The present study revealed that two heads of the adductor hallucis muscle, the oblique and transverse, had different innervating patterns, suggesting that two heads of the human adductor hallucis muscle develop from different primordia, and not from common ancestors.     

The medial branch of the lateral branch of the posterior ramus of the spinal nerve

In the needle insertion of epidural anesthesia with the paramedian approach, the needle can pass through the longissimus muscle in the dorsum of the patients. When the needle touches a nerve in the muscles, the patients may experience pain in the back. Obviously, the needle should avoid the nerve tract. To provide better anesthetic service, analysis of the structure and where the concerned nerves lie in that region is inevitable. Material and method: We studied five cadavers in this study. Two cadavers were fixed with Thiel’s method. With these cadavers, we studied the nerve running of the posterior rami of the spinal nerve from the nerve root to the distal portion. Three of them were used for the study of transparent specimen, with which we studied the course and size of the nerve inside the longissimus muscle. Results: We observed there were three branches at the stem of the posterior rami of the spinal nerves between the body segment T3 and L5, i.e. medial branch, medial branch of the lateral branch and lateral branch of the lateral branch. The medial branch of the lateral branch supplied to the longissimus muscle. With the transparent specimen, we found that there were different nerve layouts between the upper thoracic, lower thoracic, upper lumbar, and lower lumbar segments in the medial branch of the lateral branch in the longissimus muscle. In the lower thoracic and upper lumbar segments, the medial branch of the lateral branch of the upper lumbar segments produced layers nerve network in the longissimus muscle. L1 and L2 nerves were large in size in the muscle. Conclusion: In the upper lumbar segments the medial branch of the lateral branch of the posterior rami of the spinal nerve produced dense network in the longissimus muscle, where the epidural needle has high possibility to touch the nerve. Anesthetists have to consider the existence of the medial branch of the lateral branch of the posterior rami of the spinal nerve when they insert the needle in the paramedical approach to the spinal column.