Human anatomy, including structure and development and practical considerations . and vieus represent specialized parts of the cartilaginous rod of the first arch, the tensor tym-pani being developed from the muscular tissue of the same arch. The slapes is developed fromthe second arch. The mesoblast which surrounds the structures of the tymi^anic cavity duringtheir development becomes spongy and finally degenerates toward the end of foital life.^ Amer. Jour, of Anatomy, Vol. VI., 1907. 1526 HUMAN ANATOMY. The air-ce//s of the temporal l)one, inducliiif^ those of the mastoid process, are forme
Human anatomy, including structure and development and practical considerations . and vieus represent specialized parts of the cartilaginous rod of the first arch, the tensor tym-pani being developed from the muscular tissue of the same arch. The slapes is developed fromthe second arch. The mesoblast which surrounds the structures of the tymi^anic cavity duringtheir development becomes spongy and finally degenerates toward the end of foital life.^ Amer. Jour, of Anatomy, Vol. VI., 1907. 1526 HUMAN ANATOMY. The air-ce//s of the temporal l)one, inducliiif^ those of the mastoid process, are formedlater by a process of absorpti(^ii. The tympanic membrane resuUs principally from chanjjes which take place in the firstbranchial arch ; it is originally thick and consists of a mesoblastic middle stratum, C(jvered on itsouter surface by the ectoblasl and on its inner surface by the entoblast. Development of the External Ear.— The median portion of the ectoblastic jijroove of thefirst branchial furrow becomes deepened to form the outer part of the external auditory canal,. 10 WEEKS ?. Diagram illustrating development of human membranous cochlea; primary otic vesicle subdivides into vestibularand cochlear pouches and endolymphatic appendage; cochlear pouch becomes ductus cochlearis ; from vestibularpouch are derived utricle, saccule and semicircular canals; whilst endolymphatic appendage gives rise to endo-lymphatic sac and duct. (Slreeter.) while the surrounding parts of the first and second arches develop into the auricle. About thefourth week of fcetal life, the thickened posterior margin of the first arch is broken up into threetubercles by two transverse furrows. Similarly on the adjoining margin of the second arch, asecond vertical row of three tubercles is formed and, in addition, behind these a longitudinalgroove appears marking ofT a posterior ridge. From these six tubercles and the ridge are differ-entiated the various parts of the auricle, the lowest nodule of the
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Keywords: ., bookauthormc, bookcentury1900, bookdecade1910, booksubjectanatomy