Okajimas Folia Anat. Jpn., 59(4) : 251-264, October 1982

Nerve Supply of the Medial and Lateral Pterygoid Muscles and its Morphological Significance

By

SHUMEI TERADA and TATSUO SATO

Department of Anatomy, School of Medicine, Tokyo Medical and Dental University, Tokyo, Japan

-Received for Publication, September 1, 1982-

Key Words : Nerve supply, Mandibular nerve, Muscles of mastication, Medial ptery. goid, Lateral pterygoid. Summary : For the morphological classification of the muscles of mastication in man, and especially in order to understand the positional significance of the ptery- golds in these muscles of mastication, the nerves of supply were examined minutely in five head-halves. 1. The nerves of supply of the masticatory muscles are classified into three categories depending upon the position of origin from the mandibular nerve. (1) proximal nerves : the masseteric nerve, and the posterior and middle deep temporal nerves ; (2) intermediate nerves : the anterior deep temporal nerve, and the nerves to the lateral pterygoid, which are usually in a common trunk with the buccal nerve; and (3) distal nerve : the nerve to the medial pterygoid. While the nerve to the medial pterygoid arises from the medial surface of the mandibular nerve in close proximity to the otic ganglion, the other nerves tend to originate from the lateral surface. According to these differences, it would appear appropriate to classify the lateral pterygoid together with the masseter and tem- poralis as the lateral muscles of mastication, and only the medial pterygoid as the medial muscle of mastication. 2. The medial pterygoid is divided into anterior and posterior portions, but the laminate composition is not so distinct. The nerve of supply is divided into the medial, intermediate, lateral and posterior main branches. 3. The nerves of supply to the lateral pterygoid arise from the angle between the buccal and mandibular nerves and from the buccal nerve. Generally, the upper head nerves and lower head nerves originate separately. The more proximally a nerve arises, the more medially it tends to be distributed. Sometimes the lower head nerves wind upwards to enter the upper head as recurrent branches.

251 252 S. Terada and T. Sato

Introduction of the four masticatory muscles and the tensor veli palatini at their points of The muscles of mastication have hitherto entry into each muscle, starting medially. been classified into two categories : the Then we traced them proximally to observe masseter and the temporalis in the super- their ramification from the mandibular ficial part, and the medial and lateral nerve and their positional relationships, pterygoid muscles in the deep part especially with regard to the lateral (Sappey 1876, Gegenbaur 1903). Although pterygoid. Having taken the tensor veli there are many anatomical studies palatini and the medial and lateral concerning masticatory muscles (Eisler pterygoid muscles from the bones, we 1912, Yoshikawa 1962, Sawada 1976) most dissected the bundles of the muscles to of them deal with the structural expla- examine the intramuscular distribution of nation of the bundles of muscles. Detailed the supplying nerves. studies of the innervation, indispensable to the morphological evaluation, are Observations and Discussion seldom found. This is true especially of studies focusing upon the deep muscles I. Ramification of the nerves supplying of mastication which are comparatively the muscles of mastication (Figs. 1-5/A) difficult to dissect. In considering the morphological signif- In this study of the muscles of masti- icance of a muscle, its nerve supply is cation in man, we examined minutely : of primary importance (Nishi 1938). The (1) the ramification of nerves distributed first problem to be considered, therefore, in the muscles, (2) the intramuscular dis- is the manner of origin of the nerves to tribution of nerves of the medial and the masticatory muscles from the mandib- lateral pterygoid muscles and (3) the ular nerve. However, there are no positional relationship between the masti- textbooks that illustrate this in detail. catory nerves and the lateral pterygoid In summarizing the results of our study, muscle. the nerve supply of the masticatory Finally, based on our results, we submit muscles can be classified into the follow- a more comprehensive classification of ing three categories based upon the the muscles of mastication. manner of origin. (1) The first category of nerves origi- Materials and Methods nates most proximally and comprises the masseteric nerve, the posterior deep Five head-halves from the corpses (four temporal nerve, and the middle deep males and one female) were used. First temporal nerve. These three nerves the superficial muscles and nerves of the originate in a common trunk near the face and the suprahyoid muscles were anterior border of the lateral surface of dissected from the lateral side and disposed the mandibular nerve. The middle deep of, as were the muscles of the tongue temporal nerve tends to branch early. It and of the phalynx from the medial side. arises directly below the other two The foramen ovate and the mandibular nerves in cases where it is already canal were opened up and certain bones independent at the point of origin were carefully removed in order to (Specimens 1 and 2). facilitate the tracing of the mandibular (2) The second category contains nerves nerve. which arise slightly distal to the first First we examined the supplying nerves but higher than the otic ganglion and Nerve Supply of the Medial and Lateral Pterygoid Muscles 253 comprises the nerves to the lateral It is true that the nerve to the medial pterygoid and the anterior deep temporal pterygoid and the nerve to the tensor nerve. These nerves arise near the veli palatini arise very close to each anterior border of the lateral surface of other. However, the nerve to the medial the mandibular nerve in a common trunk pterygoid tends to arise from the main with the buccal nerve. In some instances, trunk of the mandibular nerve, while the they arise very close to the first category nerve to the tensor veli palatini always nerve trunk (Specimens 4 and 5). originates from the anterior margin of (3) The third category contains the the otic ganglion. So the nerve to the nerve to the medial pterygoid, which medial pterygoid can be considered as arises most distally from the medial being situated slightly lateral to the surface of the mandibular nerve very nerve to the tensor veli palatini. close to the otic ganglion. It always arises parallel to the nerve to the tensor III. Nerve supply of the medial pterygoid veli palatini. The medial pterygoid is divided into two, an anterior and a posterior portion, H. Nerve supply of the tensor veli palatini according to origin. The anterior portion and the tensor tympani (Figs. 1-4/A B, originates from the pyramidal process of Fig. 5/A) the palatine bone and is very muscular. The nerve to the tensor veli palatini The posterior portion arises from the arises from the anterior border of the pterygoid fossa of the sphenoid bone and otic ganglion close to the medial pterygoid the lower extremity of the lateral nerve, and enters the muscle from the pterygoid plate. The muscle is divided lateral surface of the posterior part. In into three layers by the tendinous sheets each specimen examined (1-4), it supplies which are recognizable in its upper one branches in a tree-like manner towards third. the anterior part and sends recurrent Schumacher (1976) reported on the branches to the posterior part. laminate composition of the medial In all specimens, the nerve to the pterygoid adding some observations from tensor tympani arises from the posterior comparative anatomy. However, accord- border of the otic ganglion a little below ing to our observations in man, three the lesser petrosal nerve. layers of lamination caused by the The nerve of the medial pterygoid , the existence of aponeuroses can only be nerve of the tensor veli palatini, and the identified at the initial upper edge of the nerve of the tensor tympani all arise muscle. It is difficult to identify them close to the otic ganglion. Textbooks by in the middle and lower parts. Hovelacque (1927), Rouviere (1932), and The nerve to the medial pterygoid Paturet (1951) contain the title "Tronc enters the upper part of the posterior commun des nerfs du pterygoldien interne, margin (Specimen 1) or the medial sur- du peristaphylin externe et du muscle du face of the superoposterior part (Speci- marteau", suggesting that the three mens 2, 3, 4 and 5) of the muscle. nerves arise from a common trunk . Standard textbooks generally describe However, judging from our observations , the position and manner of entry of the the nerve to the tensor tympani should nerve to the medial pterygoid in approxi- be distinguished from the other two mately two ways first, the entry in nerves by its manner of origin from the several branches at the upper part of posterior border of the otic ganglion. the posterior border of the muscle and 254 S. Terada and T. Sato

Fig. 1. Specimen 1. Male, right side. Medial aspect. ® Ramification of the mandibular nerve. i• Intramuscular distribution of the nerves to the medial pterygoid and the tensor veli palatini ; a-d indicate the four main branches. © Intramuscular distribution of the nerves to the lateral pterygoid. The broad dotted line shows the border between the upper and lower heads. Nerve Supply of the Medial and Lateral Pterygoid Muscles 255

1

Fig. 2. Specimen 2. Female, right side. Medial aspect. ® Ramification of the mandibular nerve. II Intramuscular distribution of the nerves to the medial pterygoid and the tensor veli palatini ; ad indicate the four main branches. © Intramuscular distribution of the nerves to the lateral pterygoid. The broad dotted line shows the border between the upper and lower heads. 256 S. Terada and T. Sato

Fig. 3. Specimen 3. Male, right side. Medial aspect. ® Ramification of the mandibular nerve. Intramuscular distribution of the nerves to the medial pterygoid and the tensor veli palatini ; ad indicate the four main branches. © Intramuscular distribution of the nerves to the lateral pterygoid. The broad dotted line shows the border between the upper and lower heads. Nerve Supply of the Medial and Lateral Pterygoid Muscles 257

Fig. 4. Specimen 4. Male, left side. Medial aspect . QS) Ramification of the mandibular nerve. I• Intramuscular distribution of the nerves to the medial pterygoid and the tensor veli palatini ; a-d indicate the four main branches. © Intramuscular distribution of the nerves to the lateral pterygoid. The broad dotted line shows the border between the upper and lower heads. 258 S. Terada and T. Sato

®

Fig. 5. Specimen 5. Male, right side. Medial aspect. ® Ramification of the mandibular nerve. ® Intramuscular distribution of the nerves to the medial pterygoid and the tensor yell palatini ; a-d indicate the four main branches.

partly through the medial surface (Toldt the same letter is used for each cor- 1911), and second, the entry in single or responding branch in the five specimens. plural branches from the medial surface Branch a is distributed in the most on the superoposterior part of the muscle medial layer of the medial pterygoid, and (Sappey 1877, Henle 1879, Quain 1895, tends to innervate the anterior portion. Spalteholz 1914, Hovelacque 1927, Rauber- It also furnishes twigs to the posterior Kopsch 1955, Clara 1959, Sieglbauer 1963, portion. Pernkopf 1963, Paturet 1964, Sobotta 1973, Branch b takes almost the same course and Rouviere 1974). According to our as a, but is distributed in the intermediate observations the form of entry varies, layer of the anterior portion slightly but we came across no case like that lateral to branch a. reported by Naito (1979), in which the Branch c descends along the gap be- nerve entered the lateral surface of the tween the anterior and posterior portions. muscle. It then winds back and forth to enter Intramuscular distribution of the nerves the lateral layer and be distributed there. of the medial pterygoid is shown in "B" Branch d first of all sends nerves to of Figs. 1-5. Major branches in each the posterior portion and tends to be muscle are shown by the letters a-d and fairly independent of the other branches. Nerve Supply of the Medial and Lateral Pterygoid Muscles 259

It is small and characteristically distributed anterior area of the upper head. restrictively in the intermediate layer of Two nerves from the buccal nerve the posterior portion. supply the lower head. The first is These findings tally, on the whole, with comparatively large and splits into three the fairly detailed descriptions by Eisler branches directly after leaving the buccal (1912) and Hovelacque (1927) of the nerve. These branches descend within intramuscular distribution of the nerve the muscle parallel to the mandibular to the medial pterygoid. nerve, giving off smaller branches as they do so. They extend transversely IV. Nerve supply of the lateral pterygoid towards the origin and insertion of the The nerve supply of the lateral pterygoid muscle. The second nerve issues from was examined in four specimens (1 to 4). the buccal nerve a little after the first. The muscle is divided into upper and One branch which ramifies from this lower heads in all specimens. The nerve divides again into the upper head tendinous laminae are so poorly developed and lower head branches. that division into strata cannot be seen. The lateral pterygoid nerves arise from Specimen 2 (Fig. 2/C) the angle between the mandibular and All the nerves to the lateral pterygoid buccal nerves as well as directly from arise from part one and enter the medial the latter. surface of the muscle. In the upper head, The buccal nerve arising from the three nerves arising from the buccal lateral surface of the mandibular nerve nerve are recognized. Three more nerves, runs, in all specimens, horizontally along arising from the angle between the the contact margin of the upper and mandibular and buccal nerves and from lower heads of the lateral pterygoid the buccal nerve, cover a large area of medial to the muscle. At fairly advanced the lower head. A small area of the point it penetrates between the two heads. anterior upper part of the lower head For convenience we divided the buccal gets its supply from the third nerve to nerve into three parts from its positional the upper head. The manner of intra- relationship with the lateral pterygoid : muscular distribution of the nerves is part one, before penetration of the muscle ; similar to specimen 1. part two, within the muscle ; and part three, after leaving the muscle. Specimen 3 (Fig. 3/C) The manner of origin and distribution Two upper head nerves proper are of the nerves to the lateral pterygoid in observed. One arises from the buccal each specimen examined is as follows. nerve in part one to enter the medial surface of the muscle, and the other Specimen 1 (Fig. 1IC) arises in part two to enter the lower All the nerves to the lateral pterygoid surface of the upper head. In the lower arise from part one and enter the medial head, two nerves from the angle between surface of the muscle after a short the mandibular and buccal nerves and distance. one from the buccal nerve itself in part The first upper head nerve arises one are recognized. All of these enter adjacent to the originating point of the the medial surface. One of the proximal buccal nerve. The second upper head nerves descends through the lower head nerve ramifies from one of the lower to communicate with the inferior alveolar head nerves and is distributed in the nerve slightly above the mandibular 260 S. Terada and T. Sato

foramen. In its intramuscular course it the manner of origin. sends two twigs to the medial part of Although Naito indicates a connectioi: the lower head. From the other two of the nerve with the inferior alveolar nerves, several ascending branches arise nerve in about 30% of his specimens, we to supply the upper head. found only one such connection (Specimen 3). Specimen 4 (Fig. 4/C) There is a relationship between the All the nerves to the lateral pterygoid point of origin of the nerves to the arise from the buccal nerve in parts one, lateral pterygoid and the entry surface. two, or three. We can say that the supply nerve arising The upper head nerves consist of the from the angle made by the mandibular proximal nerve from part one which and buccal nerves, or from part one of enters the medial surface, and the distal the buccal nerve, enters the medial nerve from part two which enters the surface of the muscle. The nerve arising lateral surface. from part two enters the lower or the Four lower head nerves are observed : lateral surface of the upper head, and the first three arise from part one to the one originating from part three enter the medial surface ; and the last enters the lateral surface of the muscle. one originates from part three to enter We did not find any nerves which arising the lateral surface after a long extra- from part two to supply the lower head. muscular course. Hovelacque states that the nerve to the The nerve to the lateral pterygoid is upper head enters its lower surface and described as "n. pterygoideus lateralis" the nerve to the lower head its upper in PNA, "nerf pterygoidien externe" in surface ; that is, the contact surfaces of Hovelacque and "nerve to the lateral the upper and lower heads. In our pterygoid" in Gray's Anatomy, all in specimens, however, the lower head singular form. On the other hand, nerves tended to enter the muscle from Schumacher (1976) and Naito (1979) the medial surface after a short extra- indicate the existence of plural supply muscular course. nerves. In our examinations, the lateral Only in the fourth specimen did we pterygoid had several nerves of supply. find a supply nerve arising from part There are two descriptions of the origin three of the buccal nerve. It entered the of the nerves to lateral pterygoid : one muscle after traveling a considerable indicates the buccal nerve (Hovelacque distance over the lateral surface of the 1927, Sicher 1965) and the other indicates muscle. Schumacher states that the nerve the buccal nerve plus the mandibular which enters the lateral surface of the nerve (Schumacher, Naito). According to muscle is the main supply nerve of the our observations, the supply nerves of the lateral pterygoid. However, according to lateral pterygoid arise mostly from the our observations, the main supply nerves buccal nerve. The most proximal nerve are, on the contrary, the group that enter often originates close to the angle made from the medial surface. by the main trunk of the mandibular With reference to the independence of nerve and the buccal nerve. Therefore, the supply nerves of the two heads, it is often very difficult to judge from Naito insists that there is a separate which of the two nerves it originates. nerve supply for each of the two heads. This is probably the reason for there By this he means the buccal nerve only being two different opinions regarding provides the nerve supply of the upper Nerve Supply of the Medial and Lateral Pterygoid Muscles 261 head only, and that the lower head is should be classified into anterior and supplied by the mandibular nerve or the posterior, or anterior, middle, and posteri- inferior alveolar nerve. Indeed, as far as or is rarely discussed in standard text- the proximal nerves are concerned, the books which cite the manner of origin and upper head nerves and the lower head distribution area of each supply ner%e. nerves are completely separate. But this There is no dispute regarding the fact is not so in the case of the distal nerves, that the anterior temporal nerve is and they often have a common nerve independent, because it originates from supply. Even when the supply nerve the buccal nerve and penetrates the appears to go to a single head, exami- lateral pterygoid. However, there remains nation of the intramuscular distribution doubt as to the constancy and independ- revealed recurrent branches to the other. ence of the middle deep temporal nerve. It is rare to find that the upper head According to our observations it origi- nerve extends to the lower head. More nates from the mandibular nerve in a often it is the other way around. common trunk with the masseteric nerve, The intramuscular distribution is only and separates itself from the masseteric mentioned briefly by Eisler (1912) and at a fairly early period. Therefore, its Schumacher (1976). Our observations constancy and independence are quite agree with Eisler in that we found that clear. Thus, the deep temporal nerves the entering nerve first crosses the main can be defined as follows : muscle bundles at a right angle within (1) The anterior deep temporal nerve is the muscle (die absteigende Astgruppe— the branch that arises from the buccal Eisler), and then the branching tributaries nerve and is distributed in the anterior proceed parallel to the main bundles (die portion of the temporalis. horizontal nach vorn laufende Astgruppe (2) The middle deep temporal nerve is —Eisler) . the branch that forms a common trunk with the masseteric nerve and separates V. Classification and nomenclature of the itself early from the main nerve to be deep temporal nerves distributed in the central portion of the Textbooks generally classify the deep muscle. temporal nerves in two ways : one divides (3) The posterior deep temporal nerve them into two, namely, the anterior and is the branch that arises from the posterior deep temporal nerves ; and masseteric nerve independently of the another into three ; namely, the anterior, middle deep temporal nerve and is dis- middle, and posterior deep temporal tributed in the posterior part of the nerves. However, a clear-cut definition muscle. of the classifying standards is never Hovelacque (1927) classifies the nerves specified. of supply to the muscles of mastication We have classified the mandibular into three categories : nerf temporo-buccal nerve branches which supply the muscles (n. temporobuccalis), nerf temporal profond of mastication into first, second, and third moyen (n. temporalis profundus medius) groups on the basis of the manner of and nerf temporo-mass6terin (n. temporo- origin and positions. The masseteric massetericus), which we judge to be an nerve belongs to the first group, and the appropriate classification on the basis of buccal nerve belongs to the second group. our present study. These provide the nerves distributed in the temporalis. Whether these branches 262 S. Terada and T. Sato

VI. Classification z of the muscles of lateral pterygoid as being the lateral mastication muscles of mastication, and the medial The muscles of mastication are usually pterygoid including the tensor veli classified into the masseter and temporalis palatini and the tensor tympani as being positioned in the lateral side of the the medial muscles of mastication (Kubota mandibule, and the lateral and medial 1976). pterygoids which are positioned medially To conclude our observations, the nerve (Sappey 1876). Embryologically, too, the to the medial pterygoid, akin to the nerve lateral and medial pterygoids are often to the tensor yell palatini and to the considered together, as are the masseter nerve to the tensor tympani, arises close and temporalis (Reuter of the pig 1897, to the otic ganglion. The nerves of Lewis 1910, Paturet 1951, Romer 1962, supply of the masseter, the temporalis Rayne and Crawford of the rat 1971). and the lateral pterygoid, originate higher However, there is an opinion which up than the otic ganglion and adjacent emphasizes the affinity among the lateral to the lateral surface of the main trunk pterygoid, the masseter, and the temporalis of the mandibular nerve. Judging from from the standpoint of comparative the way it branches from the mandibular anatomy and comparative embryology nerve, the lateral pterygoid should be and the positional relationship of these distinguished morphologically from the muscles with the main trunk of the medial pterygoid and should be counted mandibular nerve (Gegenbaur 1903, Edge- as the lateral muscle of mastication, as worth 1914, Lubosch 1938). This groups stated by Lubosch and Kubota. rr, rian,* h. I-cirri n 1 nnri thP

Abbreviations for All Figures

LP : Lateral pterygoid (M. pterygoideus inferior) lateralis) : Lingual nerve (N. lingualis) LPI : Upper head of the lateral pterygoid 1p: Lateral pterygoid nerve (N. ptery- LPu : Lower head of the lateral pterygoid goideus lateralis) MP : Medial pterygoid (M. pterygoideus md: Mandibular nerve (N. mandibularis) medialis) mh: Mylohyoid nerve (N. mylohyoideus) TVP : Tensor veli palatini (M. tensor veli mp : Medial pterygoid nerve (N. ptery- palatini) goideus medialis) at : Anterior deep temporal nerve (N. ms Masseteric nerve (N. massetericus) temporalis profundus anterior) mt : Middle deep temporal nerve (N. au : Auriculotemporal nerve (N. auticulo- temporalis profundus medius) temporalis) og otic ganglion (Ganglion oticum) bc : Buccal nerve (N. buccalis) pe : Lesser petrosal nerve (N. petrosus ct : Chorda tympani (Chorda tympani) minor) ia : Inferior alveolar nerve (N. alveolaris Nerve Supply of the Medial and Lateral Pterygoid Muscles 263

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Miinchen-Berlin-W ien, (1973) Berlin und Wien, (1911) 27) Spalteholz, W.: Handatlas der Anatomie 30) Yoshikawa, T.: The lamination of the des Menschen, siebente Aufl, Bd 3, 695- human masseter—The new identification 697, S. Hirzel, Leipzig, (1914) of M. temporalis superficialis, M. maxil- 28) Testut, L.: Traite d'anatomie humaine, lomandibularis and M. zygomatico-man- deuxieme ed, Tome 2, 734-743, Octave dibularis in the human anatomy, Acta Doin, Paris, (1893) Anat Nipponica, 37 : 260-267, (1962), (in 29) Toldt, C.: Anatomischer Atlas, siebente Japanese) Aufl, Bd 6, 867, Urban & Schwarzenberg,