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

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Nerve Supply of the Medial and Lateral Pterygoid Muscles and Its Morphological Significance 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.
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