File:Moffatt1957 plate01.jpg: Difference between revisions

Plate 1

Fig. 1 - Stage 22 embryo (no. 6701, 24 mm) Origin of articular disk. The origin of the articular disk is associated with the appearance of the external pterygoid and masseter muscles, which are recognizable in a frontal section (fig. I, pl. 1) through the region corresponding to the anterior portion of the future condyle, the disk is seen as a vague layer of mesenchyme extending laterally across the superior border of the external pterygoid muscle to the medial side of the masseter. The developing disk is separated from the condensation of mesenchyme which becomes the zygomatic process of the temporal bone by a large area of sparse cells, the precursor of the superior joint cavity. In contrast, the inferior joint cavity is preceded by only a very narrow zone of cells, because the articular disk, even in its early development, rests closely on the mandible. In this specimen an attachment of the external pterygoid muscle to the mandible could not be identified. The muscle, however, could be followed back to the posterior end of Meckel’s cartilage.

Fig. 2 - Stage 23 (no. 86, 30 mm) shows the further development of the articular disk. In frontal section the upper surface of the developing condyle faces laterally. Lying against this surface is a dark band of cells which gives rise to the articular disk. The external pterygoid muscle joins the medial side of the condyle at its approximate site of attachment in the fully developed joint. The muscle does not end at this point, however. It passes posteriorly along the medial side of the condyle and joins the band of cells forming the articular disk. The cells giving rise to the articular disk and to the external pterygoid tendon continue from this point postero-superiorly to attach to that portion of Meckel’s cartilage which becomes the malleus. This attachment of the mesenchymal layer and the external pterygoid tendon to the malleus is a constant feature, seen in all specimens up to and including a 40mm fetus. In this 30-mm embryo, membrane-bone spicules make their appearance in the zygomatic process and squama of the temporal bone. The articular disk is still separated from the temporal bone by a large area of sparse cells which are giving up their round form to become elongated. The joint capsule is not yet recognizable.

Fig. 3 - Fetal (no. 1318, 37 mm) Relations to adjacent structures. In a frontal section the condyle is still merely a condensation of mesenchyme around the upper end of the osseous lamella forming the mandible. The articular disk and external pterygoid tendon are shown continuing posteriorly to their attachment on the malleus. The structures in immediate relation to the medial side of the temporomandibular joint are demonstrated in this section. Directly inferior to the external pterygoid muscle is the internal maxillary artery cut in cross section. The middle meningeal artery is seen in longitudinal section running superiorly between the condyle and the otic ganglion. The two portions of the auriculo-temporal nerve which surround the middle meningeal artery are visible, as are also the inferior alveolar and lingual nerves.

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Reference

Moffatt BC. The prenatal development of the human temporomandibular joint. (1957) Carnegie Instn. Wash. Publ. 611, Contrib. Embryol., 36: .