人胎児鼻腔初期の発生学的研究

Abstract

The nasal pit of the early human embryo appears in the Streeter's horizon XV, in the next horizon XVI it becomes a nasal fossa which is surrounded by mesenchymal tissue of the socalled medial, lateral nasal and maxillary processes. This nasal fossa deepens in the next horizon XVII and in the horizon XVIII the thin bucco-nasal membrane at the bottom of the fossa gives way and disappears. Thus the primitive choana is open in this stage.This structure of the primitive nasal cavity is visible in the author's 10 to 20 mm long embryos, by which the absolute thickness of the nasal septum does not change, while the dimensions of the cavity increase twice in this period. During this period of the primitive nasal cavity the palate process on the pharyngeal surface of the maxillary process is becoming prominent and at the end of this period the anterior end of this swelling visible on the maxillary process lateral to the primitive palate, which structure is missed in the succeeding more developed embryos.Among three elder embryos a 35 mm long have a distinct secondary palate, by which the palate processes of both sides are above the tongue, the incisive canal at the anterior third is surrounded by osseous tissue of the maxillary and premaxillary processes. By the other two 22 and 27 mm long embryos the palate processes of both sides are lateral and under the tongue, their anterior parts protruding not vertically, but horizontally under and before the tongue and continued to the palate. By these two embryos the Jacobson's organ comes more foreward on the hinder third (22 mm) or middle (27 mm) of the palate, which condition is not by the primitive palate, by which the organ comes above the posterior margin of the palate.The olfactory fibers are from the beginning of the nasal pit discernible, the terminal nerve later before the perforation of the primitive choana. The nasopalatine nerve comes from the maxillary on the surface of the nasal septum under the epithelium and reaches the anterior naris early in the horizon XV, the palatine nerves a little later in the horizon XVII, when the palatine processes are becoming eminent. The anterior ethmoidal and infratrochlear nerves are also in the latter stage observed.During the primitive nasal cavity is the maxilloturbinale alone visible on the lateral surface, the ethmoturbinale later in the 22 mm long embryos, also the maxillary sinus.The precartilage of the wall of the nasal cavity appears first in the nasal septum in the horizon XVIII, then in the lateral wall a little later. The precartilageous septum becomes cartilageous first in the 27 mm, then the laterawall in the 35 mm long embryo.