Sphenomandibular ligament and degenerating Meckel's cartilage revisited: Sequential variations with temporal bone deformity for ligament attachment in near-term human fetuses.

BACKGROUND: The sphenomandibular ligament (SML) is considered to originate from Meckel's cartilage (MC). However, no study has examined how the os goniale contributes to SML development. METHODS: Semiserial histological sections of heads from 18 near-term fetuses at 27-40 weeks of gestation were examined. OBSERVATIONS: The os goniale and the anterior process of the malleus (AP) provided a long, bar-like membranous bone complex that passed through the petrotympanic and tympanosquamosal fissures. Notably, the AP-goniale complex is sometimes elongated inferiorly to join the SML (n = 4 specimens). Along the complex in the bone fissures, a degenerating MC was often present (n = 12). With (n = 6) or without (n = 3) the MC remnant, the tympanic bone (TYB) protruded inferomedially near the tympanosquamosal fissure, and it sometimes continued to a cartilaginous SML (n = 3). The temporal bone squamosa or petrosa provided a similar bony process approaching the SML. The middle meningeal artery often ran between the sphenoid and petrosa. CONCLUSIONS: Most of the specimens (n = 15) exhibited a sequential change from a cartilaginous SML as a continuation of the MC remnant to the ligament after the disappearance of the cartilage. The degenerating MC appeared to cause transformation from the AP-goniale complex and/or TYB to "another ligament" that replaced the usual SML at the upper part. Near the MC remnant, a similar transformation was also suggested on the squamosa or petrosa. The sphenoid spine appeared to originate often from the sphenoid ala major but sometimes from the TYB.

The canine jaw-ear connection: The malleomandibular and tympanomandibular ligaments.

In the human, two ligaments derived from the first embryonic pharyngeal (branchial) arch that unite the mandible and temporomandibular joint (TMJ) with the middle ear have been identified as the discomalleolar ligament (DML) and sphenomandibular ligament (SML), also known as the malleomandibular ligament (MML), anterior ligament of the malleus (AML), and tympanomandibular ligament (TML). Neither of these structures has been previously described in the dog. The homologue of the human sphenomandibular ligament (SML) exists in the dog and is represented as a fibrous remnant of Meckel's cartilage. In the newborn puppy, the ligament is a true malleomandibular ligament (MML), extending from the medial mandible to the rostral process of the malleus with no intermittent attachments. In the adult dog, the ligament is entrapped within a bony passageway, likely due to the development and ossification of the tympanic bulla, making it difficult to grossly view the complete course of the ligament. The majority of the ligamentous fibers attach near the tympanic bulla in the adult dog, thus this portion of the ligament has been named the tympanomandibular ligament (TML). Those fibers of the ligament not attaching near the tympanic bulla appear to continue through a canal, located between the tympanic annulus and the surrounding tympanic bone, to become continuous with a connective tissue sheet within the cavity of the middle ear that has attachments to the malleus and incus. Tension on the adult canine TML did not result in movement of the malleus.

Distribution of elastic fibers in the head and neck: a histological study using late-stage human fetuses.

There is little or no information about the distribution of elastic fibers in the human fetal head. We examined this issue in 15 late-stage fetuses (crown-rump length, 220-320 mm) using aldehyde-fuchsin and elastica-Masson staining, and we used the arterial wall elastic laminae and external ear cartilages as positive staining controls. The posterior pharyngeal wall, as well as the ligaments connecting the laryngeal cartilages, contained abundant elastic fibers. In contrast with the sphenomandibular ligament and the temporomandibular joint disk, in which elastic fibers were partly present, the discomalleolar ligament and the fascial structures around the pterygoid muscles did not have any elastic fibers. In addition, the posterior marginal fascia of the prestyloid space did contain such fibers. Notably, in the middle ear, elastic fibers accumulated along the tendons of the tensor tympani and stapedius muscles and in the joint capsules of the ear ossicle articulations. Elastic fibers were not seen in any other muscle tendons or vertebral facet capsules in the head and neck. Despite being composed of smooth muscle, the orbitalis muscle did not contain any elastic fibers. The elastic fibers in the sphenomandibular ligament seemed to correspond to an intermediate step of development between Meckel's cartilage and the final ligament. Overall, there seemed to be a mini-version of elastic fiber distribution compared to that in adults and a different specific developmental pattern of connective tissues. The latter morphology might be a result of an adaptation to hypoxic conditions during development.

Histological Characteristics of Ligaments between Middle Ear and Temporomandibular Joint.

OBJECTIVES: To examine histological aspects of the ligaments between the middle ear and temporomandibular joint and suppose a theoretical role of their structural characteristics on mobility of mallear ossicle. METHODS: The ligaments were obtained by microdissection of middle cranial fossa on both sites of 15 cadavers fixed in formalin solution and were sectioned longitudinally (7-10 mum thickness). The sections were stained with Verhoff's Van Gieson's stain (VVG) for demonstration of elastic fibers and visualized at X2.5 and X10 magnifications under light microscopy. RESULTS: Anterior mallear ligament (AML) and sphenomandibular ligaments (SML) were consisted of collagen fibres in analyzed specimens. The discomallear ligament (DML) was constituted of rich collagenous fibres. One specimen of DML harvested between petrotympanic fissure and retrodiscal-capsular intersection site contained elastic fibers dispersed in cotton-bowl appearance between collagen fibers. In the light of functional tests performed in previous studies, it could be extrapolated that presence of elastic fibers in the DML may prevent excessive forces conducted to mallear head by elongation of elastic fibers. CONCLUSIONS: Collagenous fibres have no ability to stretch along their axis which may lack compensatory mechanism to prevent mallear head mobility.

Análisis de los términos utilizados en la literatura científica para referirse a los ligamentos extracapsulares de la articulación témporomandibular: Parte I: Ligamentum sphenomandibulare / A study of terms used in scientific literature to refer to the extracapsular ligaments of the temporomandibular joint: Part I: Ligamentum sphenomandibulare

La Terminología Anatómica es la base de correcta comunicación anatómica y establece la unificación internacionalmente aceptada para diversas estructuras anatómicas. Sin embargo, su uso en la literatura pedagógica y científica no se ha aplicado por completo. El objetivo de esta investigación fue analizar la literatura en relación al uso correcto de los términos referentes al Ligamento esfenomandibular de la Articulación témporomandibular (ATM). Se realizó una revisión en libros de anatomía y artículos científicos relacionados y se comparó el uso de términos referentes al ligamento esfenomandibular con la Terminología Anatómica Internacional (TAI). Se encontraron diferencias en cuanto a los términos usados (sinonimia) para referirse tanto al ligamento esfenomandibular, así como a las estructuras que sirven de origen e inserción a este con los términos establecidos por la TAI en latín, inglés y algunos términos traducidos al español. La sinonimia y uso de epónimos encontrados dificultan la comunicación entre los científicos del área, así como el aprendizaje de los alumnos de pregrado y postgrado, cuya principal fuente de estudio continúan siendo los libros de anatomía.

Terminología Anatómica is currently the international standard for anatomical terminology, and establishes an internationally accepted and unified nomenclature for several anatomical structures. However, International Anatomical Terminology (IAT) is not always used correctly in scientific literature. The purpose of this review is to examine scientific literature in order to determine whether the terms that refer to the sphenomandibular ligament of the temporomandibular joint (TMJ) are being used correctly. Scientific books and articles were reviewed, and the terms used were compared with those established by the IAT. Our study found differences between the terms actually used (Synonyms) to refer to the sphenomandibular ligament and to the anatomical structures where the ligament originates and where it is inserted and those established by the IAT in Latin, English and some terms translated into Spanish. The use of eponyms and synonyms found, creates difficulties in communication between scientists and in the learning process of undergraduate students, who frequently use textbooks.

Distribution of elastic fibers in the head and neck: a histological study using late-stage human fetuses / 대한해부학회지

There is little or no information about the distribution of elastic fibers in the human fetal head. We examined this issue in 15 late-stage fetuses (crown-rump length, 220-320 mm) using aldehyde-fuchsin and elastica-Masson staining, and we used the arterial wall elastic laminae and external ear cartilages as positive staining controls. The posterior pharyngeal wall, as well as the ligaments connecting the laryngeal cartilages, contained abundant elastic fibers. In contrast with the sphenomandibular ligament and the temporomandibular joint disk, in which elastic fibers were partly present, the discomalleolar ligament and the fascial structures around the pterygoid muscles did not have any elastic fibers. In addition, the posterior marginal fascia of the prestyloid space did contain such fibers. Notably, in the middle ear, elastic fibers accumulated along the tendons of the tensor tympani and stapedius muscles and in the joint capsules of the ear ossicle articulations. Elastic fibers were not seen in any other muscle tendons or vertebral facet capsules in the head and neck. Despite being composed of smooth muscle, the orbitalis muscle did not contain any elastic fibers. The elastic fibers in the sphenomandibular ligament seemed to correspond to an intermediate step of development between Meckel's cartilage and the final ligament. Overall, there seemed to be a mini-version of elastic fiber distribution compared to that in adults and a different specific developmental pattern of connective tissues. The latter morphology might be a result of an adaptation to hypoxic conditions during development.

Topographic Anatomy of the Discomalleolar and Anterior Malleolar Ligaments in Human Adults and Fetuses / 체질인류학회지

During temporomandibular joint (TMJ) formation, discomalleolar ligament (DML) and anterior malleolar ligament (AML) are formed within the dorsal end of the 1st branchial arch. But, DML is known as a remnant or the degenerated tissue through the TMJ development. There is few reports said that damage of AML and DML cause the damage of middle ear during surgical procedures. Especially, in case of anterior disk displacement of TMJ, aural symptom can be made via DML due to hyperextension anteriorly. A few studies have been reported about DML and AML in embryological and histological points of view, morphology and clinical aspects of DML and AML are still unclear. Four fetuses and sixteen adult hemi -sectioned heads were dissected to clarify the topographical relationship of AML and DML and to find out the anatomico -clinical relevance related with temporomandibular disorder. In fetal specimens, DML was firmly attached from the disk of the TMJ to the malleus. Also, AML in which distinguished into the superior and inferior lamellae was running anteriorly and continuous with the sphenomandibular ligament (SML) through the future petrotympanic fissure (PTF). DML attached to the malleus was observed in all adult specimens and was expanded broadly to the disk and capsule of the TMJ as shown the V -shaped ligament structures. The average distance between the anterior aspects of the malleolar head to the anterior wall of the tympanic cavity was 1.13 mm(0.75 ~1.59), and the length of the DML from the anterior aspect of the malleolar head to the attached site to the TMJ capsule at the PTF was 5.37 mm (4.53 ~6.07). The average width of the DML at the PTF was 6.06 mm (4.72 ~7.46). Most of the posterior attachments of the DML were the cases in which DML was directly attached to the malleus (68.7%). In all specimens, DML was attached to the disk and capsule of TMJ and attached to the anteromedial border of the PTF concurrently. In this study, two morphological patterns of AML were observed according to the presence of the bony ridge on the Huguiers canal in the PTF. The bony ridge of the Huguiers canal showed DML and AML separately in 56.3%, and the fused pattern of DML and AML was observed in 43.7%. AML was not distinguished with two lamellae in most specimens, superior ligament fibers were attached to the anteromedial border of the PTF and most of the inferior lamella was entering the gap in PTF and continuous with the SML. Average length from the anterior aspect of the malleolar head to the exit point of the AML on the PTF was 8.40 mm(6.62 ~11.42), and the shortest distance between the AML and chorda tympani was 2.01 mm(1.25 ~3.02). Taken all together, DML and AML were not the rudimentary, but the distinguishable structures in adults. Through the various morphological findings, DML and AML were separated ligamentous structures in which might be given rise from the divergent origin. And the anterior hyperextension of the disk of TMJ did not lead the movement of the malleus in the tympanic cavity, whereas, the movement of the malleus followed by the traction of the AML and SML was observed in a few cases. So, this results can be explained the possibility of the clinical symptom on the middle ear in case of the over -traction of the AML and SML.