. Comparative anatomy. Anatomy, Comparative. THE SENSE ORGANS 577 pit with the corner of the mouth. The narial passages, however, are not formed by the fusion of the edges of this groove, as in some amphibia 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 narial passages into the mouth correspond with those of amphibia and reptiles. The secondary and definitive choanae rise poste- rior to the primary pair, when paired
. Comparative anatomy. Anatomy, Comparative. THE SENSE ORGANS 577 pit with the corner of the mouth. The narial passages, however, are not formed by the fusion of the edges of this groove, as in some amphibia 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 narial passages into the mouth correspond with those of amphibia and reptiles. The secondary and definitive choanae rise poste- rior 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 NASO-OPTIC. GROOVE NASO-BUCCAL GROOVE MANDIBULAR PROCESS. DOUBLE HARE-LIP Fig. 476.—The development of the narial passages in A, Chick and B, Man. In phylogenesis the narial 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 narial 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. (A redrawn after B. Patten, and B after Corning.) from the mouth cavity. Palatine processes appear first in a two-months human embryo, and the formation of the palate is completed at five months. The inferior or maxillary conchae arise early in ontogenesis. Five more pairs are formed by outgrowth from the ethmoid. Of these, three later disappear, leaving the maxillary and two ethmoid characteristic of the adult. TASTE ORGANS The second of the chemical senses is taste which, as we have seen, has a common origin with smell. All animals respond in one way or another to substances dissolved in water. Specialized taste organs in the form.
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