. Chordate anatomy. Chordata; Anatomy, Comparative. THE SENSE ORGANS 40,3 which connects the anterior part of the nasal passage with the mouth cavity. (Fig. 354) Ontogenesis. In elasmobranchs, each olfactory organ develops from a placode-like thickening at the anterior termination of the series of lateral- line organs. Subsequently each placode, by invagination, is converted into a pit, which Hes in close apposition to the telencephalic vesicle. In man a groove similar to the nasobuccal groove of elasmobranchs connects each olfactory pit with the corner of the mouth. The nasal passages, howeve
. Chordate anatomy. Chordata; Anatomy, Comparative. THE SENSE ORGANS 40,3 which connects the anterior part of the nasal passage with the mouth cavity. (Fig. 354) Ontogenesis. In elasmobranchs, each olfactory organ develops from a placode-like thickening at the anterior termination of the series of lateral- line organs. Subsequently each placode, by invagination, is converted into a pit, which Hes in close apposition to the telencephalic vesicle. In man a groove similar to the nasobuccal groove of elasmobranchs connects each olfactory pit with the corner of the mouth. The nasal passages, however, are not formed by the fusion of the edges of this groove, as in NASO-OPTIC GROOVE NASO-BUCCAL GROOVE MANDIBULAR, PROCESS. DOUBLE HARE-LIP Fig. 355.—The development of the nasal passages in A, chick and B, man. In phylogenesis the nasal passages are believed to have arisen through the approximation and closure of the edges of the nasobuccal grooves. Such grooves appear in ontogenesis. Failure of such grooves to close over is the best explanation of hare-lip and perforate palate shown in B. In normal growth in the human embryo, however, the nasal passages are not formed by the closing over of grooves but by the backward growth of an ectodermal cord which grows from the nasal pit to the mouth cavity. (.4 redrawn after B. Patten, and B after Corning.) some amphibians and fishes, but by the backward extension of the olfactory pits, which acquire a secondary connexion with the mouth. Hare-lip in man results from the imperfect obliteration of the nasobuccal groove. The primary openings of the nasal passages into the mouth correspond with those of amphibians and reptiles. The secondary and definitive choanae arise posterior to the primary pair, when paired palatine processes unite in the middle of the roof of the mouth, and thus separate the naso- pharyngeal cavity from the mouth cavity. Palatine processes appear first in a two-months human embryo, and the formation of the palate
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Keywords: ., bookcentury1900, bookpublisherphi, booksubjectanatomycomparative
