Introduction

The pharynx is a musculomembranous tube extending from the cranial base to the level of the lower border of the cricoid cartilage and comprises three zones, the nasopharynx (nasal part), the oropharynx (oral part) and the laryngopharynx (laryngeal part) [5, 6, 9, 15, 21]. The pharyngeal muscles consist of three circular muscles, the superior, middle and inferior constrictors, and three longitudinal muscles, the stylo-, salpingo- and palatopharyngei [5, 6, 9, 14, 15]. They are innervated by the cranial part of the accessory nerve via the pharyngeal plexus, except for the stylopharyngeus innervated by the glossopharyngeal nerve [15]. In the pharyngeal phase of the swallowing (deglutition) reflex, the pharynx changes from being an air channel to being a food channel [15]. For the closure of the upper level of the air way, a seal is produced by activation of the superior constrictor and contraction of a subset of the palatopharyngeal fibers forming a variable, ridge-like, structure (Passavant’s ridge) to which the soft palate is elevated. On the other hand, the seal of the air way at the laryngeal inlet is produced by closure of the glottis.

The superior constrictor arises from the medial pterygoid plate, the pterygoid hamulus, the pterygomandibular raphe, the posterior end of the mylohyoid line of the mandible and the side of the tongue, and is inserted into the pharyngeal raphe [2, 6, 9, 14, 15, 17]. According to the origins, the superior constrictor is divided into four parts, the pterygopharyngeus, the buccopharyngeus, the mylopharyngeus, and the glossopharyngeus [1, 2, 5, 9]. It was reported that some types were found in the origins of the buccopharyngeus and the mylopharyngeus, depending on whether the attachment contains membranous connective tissue or not and the tip of the origin is on the mylohyoid line or away from it, respectively [19]. The palatopharyngeus arises from the palate by two bundles that are separated by the levator veli palatini and are joined by the salpingopharyngeus that arises from the cartilage of the pharyngotympanic (auditory) tube [14, 15, 17]. In some studies, the origin of the palatopharyngeus was divided into the bundles from the oral and nasal sides of the soft palate [11], the lateral and medial bundles [3, 4, 8], or the longitudinal and transverse bundles [16]. The palato- and salpingopharyngei are inserted into the thyroid cartilage with the stylopharyngeus, attach to pharyngeal fibrous tissue, and decussate with the contralateral muscle [14, 15, 17]. It was reported that the blended bundle of the three longitudinal muscles also attached to the palatal tonsil, the epiglottis, the arytenoid cartilage and the piriform fossa [4, 11, 16].

The superior constrictor constricts the superior part of the pharynx, and the palatopharyngeus pulls the pharynx up, forwards and medially, and thus shorten it during swallowing [14, 15]. It has been suggested that a band of muscle fibers, the palate-pharyngeal sphincter, assists in shutting off the nasopharynx by producing the ridge of Passavant [20]. It was also reported that the uppermost fibers of the superior constrictor arise from the palate [7, 13]. However, the relations of these fibers with the palatopharyngeus and the palate-pharyngeal sphincter have not been clear. As a result, the configurations of the superior constrictor and the palatopharyngeus have been left vague. As the precise knowledge of the structure of the pharynx is important to make a correct diagnosis of the velopharyngeal function, it is necessary to investigate the spatial relations between the superior constrictor and the palatopharyngeus to understand their functions. The purpose of this study was to clarify the configurations of the superior constrictor and the palatopharyngeus and their morphological interrelationships.

Materials and methods

Fifty-six sides of 28 Japanese cadavers (13 males and 15 females; average age 80.0 years) were investigated in this study. The cadavers were donated for the anatomical education and researches in Tokyo Medical and Dental University. They were fixed in 8 % formalin and preserved in 30 % alcohol. Following the dissection of the head and neck, the cervical vertebrae and the mandible were completely removed. The occipital bone, apart from the basilar part, and some parts of the skull were removed to show the pharyngeal wall. After removing the impeditive bony elements, the muscles and nerves were dissected. The origins and the insertions of the superior constrictor, the palato-, salpingo-, stylopharyngei and the palatoglossus, and the arrangement of their fibers and their positional interrelationships were examined in detail under a binocular microscope.

Results

The superior constrictor and the palatopharyngeus were flat and overlapped one another, and their spatial interrelationship is summarized in Fig. 1 based on the findings. Apart from the superior and inferior fibers, the superior constrictor was interconnected with the buccinator by the pterygomandibular raphe though their fibers were sometimes linked directly (Fig. 2a). The superior fibers arose from the pterygoid hamulus primarily and the inferior portion of the medial pterygoid plate secondarily, and the most superior fibers attached to the superior surface of the lateral half of the palatine aponeurosis (Fig. 2a, b). The inferior fibers arose from the posterior area of the mylohyoid line of the mandible, and the most inferior fibers attached to the margin of the root of tongue (Fig. 2a). The palatopharyngeus arose from the palatine aponeurosis, and some fibers attached to the hard palate and the pterygoid hamulus. Its lateral fibers attached to the superior surface of the lateral half of the aponeurosis and were fused with the fibers from the palatal origin of the superior constrictor (Fig. 2b). Its medial fibers arose from the superior and inferior surfaces of the medial half of the aponeurosis, and most of them were conjoined with the contralateral one. The levator veli palatini was inserted into the superior surface of the medial half of the aponeurosis and connected with the fellow. On this occasion, the fibers of the levator veli palatini and the superior layer of the medial fibers were interdigitated with one another (Fig. 2d, e). Some superior medial fibers passed superiorly to the levator veli palatini or rarely fused with it (Fig. 2e). The slip of the salpingopharyngeus, which was found in the salpingopharyngeal fold, descended from the posteroinferior part of the cartilage of the pharyngotympanic tube and merged into the superior medial fibers (Fig. 2e, f). The origin of the palatoglossus, which was found in the palatoglossal arch, attached the inferior surfaces of the palatine aponeurosis and the origin of the inferior medial fibers, and was connected with the contralateral one (Fig. 2g).

Fig. 1
figure 1

The spatial relationship between the superior constrictor (SC) and the palatopharyngeus (PP). Posterior view of the right half of the pharynx. Ep epiglottis, iMPP inferior layer of medial fibers of PP, LPP lateral fibers of PP, LVP levator veli palatini, Mb mandible, MPP medial fibers of PP, SP soft palate, PH pterygoid hamulus, PMR pterygomandibular raphe, PR pharyngeal raphe, PT pharyngeal tubercle, PW pharyngeal wall, sMPP superior layer of medial fibers of PP, StP stylopharyngeus, TC thyroid cartilage, To tongue, Uv uvula. Blue and red arrows are the fibers’ directions of SC and PP, respectively. Dashed lines indicate the lines of origins and insertions. Asterisk indicates decussating fibers

Full size image
Fig. 2
figure 2

The external (a, b, d) and internal (c–f) aspects of the superior half of the pharynx. c–f are the median sagittal sections of the head, and c shows both aspects from the median line. BM buccinator, Ep epiglottis, iMPP inferior layer of medial fibers of palatopharyngeus, LPP lateral fibers of palatopharyngeus, LVP levator veli palatini, MC middle constrictor, MP medial pterygoid plate, PF pharyngobasilar fascia, PH pterygoid hamulus, PMR pterygomandibular raphe, SaP salpingopharyngeus, SC superior constrictor, sMPP superior layer of medial fibers of palatopharyngeus, SP soft palate, PG palatoglossus, PR pharyngeal raphe, PT pharyngeal tubercle, PtT pharyngotympanic tube, StG styloglossus, StP stylopharyngeus, TVP tensor veli palatini, Uv uvula. a Left side of case 1. LVP, TVP, StG and StP were moved to show SC. PMr is not visible (dashed line). Some fibers SC interweave with StP (black asterisk). White asterisk indicates decussating fibers. b left side of case 2. The most superior fibers attach to MP and PH. Asterisk indicates decussating fibers. c, d right side of case 3; e, f left side of case 4. The palatopharyngeus (LPP, sMPP and iMPP) arises from SP, and the medial fibers (sMPP and iMPP) interdigitate with the fibers of LVP (arrow in d). SaP merged into sMPP (d and e). Some of sMPP pass superiorly to LVP (asterisks in d and e). PG arises from the inferior surface of the origin of iMPP (arrow in f)

Full size image

The fibers of the superior constrictor ran backward and curved medially (Figs. 2a, 3a). They converged to pass between the pharyngotympanic tube and the stylopharyngeus and fanned out again, and the inferior fibers interwove with the stylopharyngeus. The lateral and medial fibers of the palatopharyngeus that united in the soft palate ran laterally and curved to fan out posteroinferiorly. From the origin to the insertion, the palatopharyngeus rotated 90 degrees about its long axis, and its superior and inferior surfaces turned into internal and external, respectively (Fig. 3b). The lateral fibers passed parallel to the fibers of the superior constrictor on its internal surface, and the medial fibers spread out inferiorly. The lateral fibers and the superior constrictor were inserted into the pharyngeal raphe with an overlap, and their fibers were sometimes linked with the contralateral ones (Fig. 3c, d). The superior constrictor and the palatopharyngeus were formed a sheet by the interfusion, and the fibers from the pterygoid hamulus ascended to the top of the raphe. More inferior fibers of the superior constrictor and more medial ones of the palatopharyngeus sequentially attached to inferior part (Fig. 3d). As a result, the sheet was folded back along the line from the hamulus to the pharyngeal tubercle. The superior medial fibers spread out into the pharyngeal wall inferior to the insertion of the lateral fibers, and more medial fibers were sequentially dispersed inferiorly (Fig. 3b, e). The inferior medial fibers descended vertically along the palatopharyngeal arch (Fig. 3b). Their lateral fibers attached to the epiglottis and extended to the arytenoid cartilage or dispersed into the piriform fossa, and more medial fibers sequentially attached to the superior and posterior borders of the lamina of the thyroid cartilage (Fig. 3e, f). The inferior medial fibers and the palatoglossus surrounded the tonsilar sinus (fossa), and the superior constrictor near its origin formed the bottom of the sinus (Fig. 3f). On the other hand, the stylopharyngeus descended between the superior and middle constrictors and merged into the external surface of the medial fibers of the palatopharyngeus, and the most anterior fibers sometimes attached to the side of the tongue (Fig. 3e, f).

Fig. 3
figure 3

The external (a, d) and internal (b, c, e, f) aspects of the pharynx. b, c, e and f are the median sagittal sections of the head. Ep epiglottis, Hb hyoid bone, IC inferior constrictor, iMPP inferior layer of medial fibers of palatopharyngeus, LPP lateral fibers of palatopharyngeus, LVP levator veli palatini, MC middle constrictor, PF pharyngobasilar fascia, PG pataloglossus, PR pharyngeal raphe, SaP salpingopharyngeus, SC superior constrictor, sMPP superior layer of medial fibers of palatopharyngeus, SP soft palate, StP stylopharyngeus, TC thyroid cartilage, To tongue, Uv uvula. a dorsal aspect of case 5. Right middle constrictor was cut and moved to show SC that is inserted into PR. b right side of case 6. LVP and SaP were cut to show LPP. The palatopharyngeus (LPP, sMPP and iMPP) rotates 90 degrees about its long axis in the course from the origin to the insertion (arrows), and its superior and inferior surfaces turned into internal and external, respectively. c right side of case 7. The muscle layer of the superior part of the pharynx consists of LPP and SC. d dorsal aspect of case 8. MC and IC were cut and moved to show SC, LPP, sMPP and StP. Left SC was also cut and moved to show that SC and LPP form a continuous sheet (double-headed arrow). e right side of case 4. f left side of case 9. sMPP spreads inferiorly to LPP and dispersed into the pharyngeal wall (e). MPP and StP attach to TC (black arrow in e and f) and Ep (white arrow in e and f). StP attach to To (dashed arrow in e). The dashed circle in f is the tonsilar sinus

Full size image

Discussion

This study examined the arrangement of the fibers of the superior constrictor and the palatopharyngeus as well as their origin and insertion. The interfusion was found between the most superior fibers of the superior constrictor and the most lateral fibers of the palatopharyngeus. As a result, their origins and insertions were arranged in a continuous line. In addition, the consecutive arrangement of their fibers indicated that these flat muscles are formed into a continuous muscular sheet.

The superior constrictor arises from the medial pterygoid plate, the pterygoid hamulus, the pterygomandibular raphe, the posterior end of the mylohyoid line and the side of the tongue [2, 6, 9, 14, 15, 17]. The palatopharyngeus arises from the palatine aponeurosis and hard palate, and the poster fibers are linked with the contralateral ones [14, 15, 17]. The palatopharyngeus also arises from the pterygoid hamulus [9]. Although the findings in this study are not inconsistent with these descriptions, as previously reported [7, 13] the most superior fibers of the superior constrictor attached to the lateral half of the palatine aponeurosis. In addition, the interfusion between the fibers of the two muscles was found in this portion. It is consistent with the studies reporting that the superior fibers of the superior constrictor often intermingled with the palatopharyngeus [7, 10, 18]. This study exhibited that the palatopharyngeus rotated 90 degrees about its long axis, and its lateral fibers passed on the internal surface of the superior constrictor. The findings indicate that the muscular layer in the posterior wall of the nasopharynx is composed of two sublayers. The fibers from the vicinities of the hamulus ascended to the top of the pharyngeal raphe, and more inferior fibers of the superior constrictor and more medial fibers of the palatopharyngeus sequentially attached to inferior part. Consequently, the two muscles are formed into a continuous sheet that is folded along the line from the hamulus to the pharyngeal tubercle. It was reported that the superior constrictor seems, in its upper part, to consist of two lamellae: a lateral lamella attached to the hamular process, and a medial lamella passing into the palate [20]. The lateral and medial lamellae correspond to the superior constrictor and the lateral fibers of the palatopharyngeus, respectively.

The palatopharyngeus arose from the palatine aponeurosis and the most medial fibers were conjoined with the fellows. The origin of the palatopharyngeus is separated into superficial and deeper, anteroinferior and posterosuperior, or anterior and posterior bundles by the levator veli palatini [14, 15, 17]. It was divided into lateral and medial fibers in this study, and the medial ones were interdigitated with the insertion of the levator veli palatini in the soft palate. Some investigators divided the palatopharyngeus into the bundles from the oral and nasal sides of the soft palate, and that from the oral side is inserted into the pharyngeal luminal side of the pharyngeal raphe at a higher point than the latter [11]. Others divided the palatopharyngeus into the longitudinal and transverse divisions [16]. Although the longitudinal division forms the palatopharyngeal arch, the transverse one takes a more cranial course and is inserted into the pharyngeal raphe. Another study divided the palatopharyngeus into the lateral and medial bundles [4]. The lateral bundle is subdivided into the longitudinal part that joins the medial bundle and the transverse part that is inserted into the pharyngeal raphe. The bundle from the oral side, the transverse division, or the transverse part of the lateral bundle seems to be comparable to the lateral fibers in this study, which passed on the internal surface of the superior constrictor. However, the medial fibers are confusing. They were separable into the superior and inferior layers. The superior layer dispersed into the pharyngeal wall inferior to the lateral fibers, and the inferior one descended along the palatopharyngeal arch. Some of the superior fibers passed superiorly to the levator veli palatini when the medial fibers interdigitated with it. This situation has made the medal fibers more complicated.

The two bundles of the palatopharyngeus unite at the posterior border of the soft palate and are joined by the salpingopharyngeus [14, 15, 17]. The palatopharyngeus is inserted into the posterior border of the thyroid cartilage with the stylopharyngeus, attach to pharyngeal fibrous tissue, and decussate with the contralateral muscle across the midline [5, 14, 15, 17]. Some studies reported that the blended bundle of the three longitudinal muscles also attached to the palatal tonsil, the epiglottis, the arytenoid cartilage, the piriform fossa [4, 11, 16]. It was also reported that the fibers of the salpingopharyngeus joined the fibers in the palatopharyngeal arch and the pharyngeal wall, respectively [10]. In this study, the salpingopharyngeus joined the superior medial fibers, and the stylopharyngeus the external surface of the medial fibers. The inferior medial fibers attached serially to the thyroid cartilage and the side of the epiglottis, and some fibers extended to the arytenoid cartilage and the piriform fossa. Although the attachment to the palatal tonsil was not reconfirmed in this study, the positional relationship suggests that it is possible. In the superior medial fibers, more medial fibers were sequentially passed inferiorly. In the inferior ones, more lateral fibers attached serially to the anterior portion. Consequently, the lateral fibers and the superior and inferior medial fibers showed contiguous sequence to spread out to the insertion. The fiber arrangement of the palatopharyngeus was deranged by the insertion of the levator veli palatini. However, it was indicated that the fibers were formed a continuous sheet, and its medial margin was folded back near the origin and spread near the insertion.

It was described that a transverse ridge was found on the posterior pharyngeal wall in the speech of the case of the cleft palate [12]. It was reported that the upper part of the superior constrictor seems to consist of two lamellae [20]. It was also suggested that the palate-pharyngeal sphincter, which is the internal layer of the upper part of the superior constrictor, assists in shutting off the nasopharynx by producing the ridge of Passavant. Some investigators described the thickened upper border of the superior constrictor as Passavant’s ridge [3]. Although the interrelations between these muscular parts are not been clear, the lateral fibers of the palatopharyngeus in this study correspond to the internal one of the two lamellae. As shown in this study, the superior margin of the superior constrictor and the lateral margin of the palatopharyngeus were inseparable. It is reasonable to regard them as a muscular sheet that was folded back. It is similar to the collar of a dress shirt. In the pharyngeal phase of the swallowing, a seal is produced by activation of the superior constrictor and contraction of a subset of the palatopharyngeal fibers forming Passavant’s ridge to which the soft palate is elevated by the levator veli palatini [2, 15]. In this study, the superior constrictor (external layer) and the lateral fibers of the palatopharyngeus (internal layer) ran parallel to the pharyngeal raphe, implying that they cooperate to constrict of the pharynx. However, the internal layer arising from the palate may be more effective than the external layer from the movable structures. At the lower level, the seal of the air way at the laryngeal inlet is produced by closure of the glottis [15]. The palatopharyngeus depresses the soft palate and raises the pharynx and shortens it during swallowing, and the stylopharyngeus elevates the pharynx and the larynx [15, 17]. The palatopharyngeus also produces a constriction of the palatopharyngeal arch and helps to shut off the pharynx from the mouth [14, 17]. The fiber arrangement indicated that the medial fibers of the palatopharyngeus and the stylopharyngeus play a main role in this function. The superior and inferior medial fibers elevate the pharyngeal wall and the larynx, respectively.

As the superior constrictor and the palatopharyngeus can be regarded as a sheet, their origins and insertions were arranged in the continuous arching line from the midline of the soft plate to the side of the tongue and from the pharyngeal tubercle to the side of the epiglottis, respectively. This muscular sheet spreads out from the anterior margin (line of the origins) to the posterior margin (line of the insertions), and its superior half and a part of the inferior margin were folded back. In addition, right and left sheets are partially joined together in the anterior and posterior margins, respectively. It resembles the open-front mantle with turnover collar. Because the fibers show contiguous sequence, it seems that this muscular sheet seems to be a functional unit, and the fibers can act serially or at the same time, depending on the situation. The findings in this study are useful for the examination of velopharyngeal function and the closure of the oropharyngeal isthmus, and the study and diagnosis of the swallowing function.