Musculus Uvulae and Palatine Raphe
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The Longitudinal Fibromuscular Component of the Soft Palate in the Fifteen-Week Human Fetus: Musculus Uvulae and Palatine Raphe HERBERT L. LANGDON, Ph.D. KATHLEEN KLUEBER, M.S. Pittsburgh, Pennsylvania 15261 The structural relationships of the longitudinal fibromuscular component of the soft palate (musculus uvulae and raphe) were studied using histologic sections from 19 early human fetal specimens. Musculus uvulae arises in association with the palatine aponeurosis near the beginning of the second quadrant of the velum, follows a sigmoid course, and terminates near the base of the uvula. In addition, an occasional muscular loop may arise from the bony palate, arch downwards, and then recur into the uvular muscle. A complex relationship exists between the raphe in the velum and several palatal muscles. With regard to musculus uvulae, small muscular bundles arise from the raphe to embrace the muscle near its crest. These branches may aid in contouring the dorsal surface of the velum in the region of the levator eminence to complement the surface of the posterior pharyngeal wall and thus enhance the efficiency of the velopharyngeal seal. Introduction received considerable attention in the litera- ture from the perspectives of comparative In the early human fetus, as well as in the anatomy (Kuenzel et al., 1966), prenatal de- adult, musculus uvulae and the palatine velopment (Doménech-Ratto, 1977; Peter, raphe form a longitudinally-oriented fibro- 1913; Futamura, 1906), and the gross anat- muscular complex running the length of the omy of the muscle in the adult (Azzam and soft palate. The uvular muscle overrides the Kuehn, 1977; Kriens, 1975; Voth, 1961; Rue- other palatal musculature in the dorsal mid- dinger, 1879; Henle, 1873). Nevertheless, line of the velum, while the raphe, situated areas of disagreement and uncertainty con- ventrally, runs a parallel course immediately tinue to exist concerning aspects of this mus- deep to the oral mucosa. cle's structure and relationships within the _- The 15-week fetus was selected for this velum. study on the morphology of the velopharyn- The palatine raphe is a landmark easily geal musculature primarily because it serves visualized from the ventral surface of both the as a model of convenient size for examining hard and soft palates. The anterior half of the the structure of this mechanism at the micro- raphe, related to the hard palate, has been scopic level. While fetal anatomy differs con- examined extensively because of its associa- siderably from adult structure in size and, to tion with the epithelial pearls found there a much lesser extent, in spatial relationships, during fetal and neonatal life (Burdi and if used judiciously, this model nevertheless Faist, 1967; Wood and Krause, 1962; Peter, provides an excellent means for surveying 1924; Bergengruen, 1909). However, since basic velopharyngeal fibromuscular arrange- pearls have not been observed to form within ment. : the soft palate to any extent, the relationships The morphology of musculus uvulae has and attachments of the raphe in the velum This research has been supported in part by the U. S. have tended to be overlooked. __ Public Health Service Grant DE-1697, National Institute Jonnesco (1912), describes the raphe as at- of Dental Research, and Health Research and Services taching anteriorly in the region of the palatine Foundation Grant 0-85. papilla and then passing caudally in midline The authors are affiliated with The Cleft Palate Cen- ter and Department of Anatomy (Dental Medicine), to become continuous with a corresponding University of Pittsburgh, Pittsburgh, PA 15261. structure in the soft palate. In addition, the 337 338 Cleft Palate Journal, October 1978, Vol. 15 No. 4 The objective of the present study is to Legend for Identification of Figures describe the morphologies of musculus uvulae MU M. uvulae and the palatine raphe, emphasizing their A Arches of raphe structural inter-relationships, which, in turn, R Axis of raphe suggest possible functional implications in the TM Transverse musculature mechanism of velopharyngeal closure. PA Palatine aponeurosis BP Bony palate Materials and Methods RM Recurrent muscle Gestational ages of the 19 human fetuses (lateral) used were determined according to estab- B Branches of raphe lished criteria (Streeter, 1920) to be 15 t 2 T Termination of raphe weeks. All specimens appeared typical-for-age MT M. tensor veli palatini as determined by gross inspection. Following PNS Posterior nasal spine routine histologic processing, ten of the heads G Glandular tissue and ducts were sectioned (30 micra) in the coronal plane TG Tongue while the remainder were sectioned sagittally. | C.T. Inclusion All even-numbered sections were stained ac- H Hamulus cording to a modified Masson trichrome tech- nique. raphe has been reported to take supplemental Pilot work suggested the use of tracings attachment to the posterior nasal spine (Jon- made from every fourth section for the com- nesco, 1912; Henle, 1886), although Luschka prehensive analysis of musculus uvulae and (1868) describes it more precisely as being the raphe, although intervening sections were continuous with the median palatine suture. included when warranted. Following a de- Fibers of musculi levator veli palatini tailed light microscopic examination of each (Todd and Fowler, 1927-28; Ruedinger, stained section of a specimen, tracings were 1879) and palatopharyngeus (Fara and Dvor made at optical enlargements of either 25 % ak, 1970; Jonnesco, 1912) have been observed (sagittal series) or 100 X (coronal series). to attach to the raphe, although this relation- Results ship has been questioned (Podvenic, 1952). In addition, an intrinsic muscular component In mid-sagittal plane, fibers of musculus (musculus uvulae inferior or minor) has been uvulae appear most anteriorly in the velum observed within the anterior one third of the near the beginning of its second quadrant velar raphe where it is described as being with the muscle characteristically having a sharply outline in its perimeter and as existing sigmoid profile or course when viewed lat- separately and distinctly from musculus uvu- erally (Figure 1a). It passes first over and then lae (proper) (Ruedinger, 1879). However, nei- downward and around the posterior bound- ther the number of specimens examined nor ary of the large muscular mass comprised of the frequency with which this muscle arrange- musculi palatopharyngeus, palatoglossus, and ment :was found to occur was reported by levator veli palatini. Upon reaching the lower Ruedinger. Finally, as the raphe approaches half of the palate, the uvular muscle joins its termination, near the base of the uvula, it with fibers of the palatine raphe before resum- is said to become deflected to the left of center ing a posterior course toward the base of the (Piersol, 1911). However, Piersol does not uvula. In this plane of section, the muscle comment further on the nature of its posterior appears to be spindle-shaped, expanding into attachment. a belly near the crest of its slope. The course The raphe itself has been described as a of the individual muscle fibers generally fol- "sharp white line," appearing shortly after lows the axis of the muscle except at its junc- fusion of the palatal shelves in the fetus (Peter, - tion with the raphe, where fiber orientation 1913). Although the term "raphe" suggests may become quite irregular. The sites of ori- this structure to be a product of shelf-fusion, gin of musculus uvulae vary considerably no description of actual raphe-formation has among the specimens examined, and their been found. ‘ attachments may be visualized as arising from Langdon and Klueber, ronctruomat rimromuscurar component mn verum 339 FIGURE la. Sagittal section through velum illustrating the course and relationships of M. uvulae (32 % , specimen 3-1546, section 516). FIGURE 1b. Schematic diagram of the sagittal section shown in Figure la, demonstrating the points at which coronal sections illustrated in Figures 4 through 11 were taken. 340 Cleft Palate Journal, October 1978, Vol. 15 No. 4 positions anterior, superior, and/or inferior to showed no obvious connection with the raphe. the muscle per se. When present, this recurrent muscle contrib- The principal anterior attachment of the utes significantly to the bulk of musculus muscle is to the posterior edge of the bony uvulae. A second group of inferiorly-related palate via an intermediate zone of fibrous fibers is observed to traverse, singly or in small connective tissue. This origin may be well bundles, the boundary between the uvulae defined as consisting of one or more tendons, muscle. and the underlying musculature (Fig- or it may be diffuse, losing its identity within ures 5 and 6). the substance of the palatine aponeurosis. In In Figure 3, musculus uvulae is depicted in two specimens (n = 10) a limited number of a coronal section through the velum at the muscle fibers originated anteriorly in the level of the pterygoid hamuli. Subsequent transverse plane, sharing this orientation with illustrations (Figures 4 through 11) character- most of the connective tissue fibers of the ize changes in the morphology of musculus aponeurosis as well as with those fibers of uvulae at points along its posterior course in musculus palatopharyngeus attaching in this the velum (see Figure 1b). part of the velum. Subsequently, these fibers In cross-section, the anterior part of the bend through a 90-degree are to join with uvular muscle typically has a lentiform shape those of the uvular muscle. and a predominantly longitudinal fiber ori- Superiorly, some fibers in all specimens entation (Figure 4). Although the muscle is were found to arise from the inferior surface bounded dorsally by fascia throughout its of the overlying aponeurosis. In 33 percent of course in the velum, it is overlapped by the the specimens, a fiber origin is seen inferiorly palatine aponeurosis only slightly at its ante- as a muscular component having a variable rior end.