The development and arrangement of the sphenomandibular ligament of 60 human embryos and fetuses were studied. Meckel's cartilage appeared as a single, continuous fibrous structure lying between the mandibular lingula and the malleus of the middle ear in fetuses of 210 mm crown-rump length (22 weeks of age) and over. This structure constitutes the malleolomandibular ligament, and two clearly differentiated portions bound by the tympanosquamosal fissure could be seen: a juxtaarticular portion, inserted on the posterior edge of the interpterygoid aponeurosis, and a tympanic portion, onto which the disc of the temporomandibular joint inserted. Some of the authors consider that if tension is applied to the sphenomandibular ligament this may injure the middle ear. The anatomical arrangement of the sphenomandibular ligament could explain these injuries.
The anterior process of the malleus of the middle ear develops irrespective of Meckel’s cartilage through an intramembranous ossification center that appears in the human embryo of 26.5 mm crown-rump length at a caudo-medial position in relation to Meckel’s cartilage. The malleus has a double origin: the anterior process originates from the os goniale through intramembranous ossification, and the rest from MeckeΓs cartilage through endochondral ossification.
The arrangement and relationships of the orbital muscle of Müller in human fetuses have been analyzed. This is a constant muscle made of smooth muscle fibers arranged over the longer axis of the inferior orbital fissure; some of its fibers reach the inferior wall of the cavernous sinus. The muscle layer is pierced by orbital rami of the medial maxillary artery and by thin veins communicating with the ophthalmic vein system and pterygoid plexus. The zygomatic nerve can be found in the midst of the muscle mass along most of its course. It is innervated by short rami from the sphenopalatine ganglion.
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