. Elementary text-book of zoology. Zoology. 92 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. antenna? in which the gangliated swollen extremities of nerves occur are to be explained as olfactory fibres. In the Vertebrata the olfactory organ usually has the form of a paired pit or cavity placed on the under surface of the head (nasal cavity), on the walls of which the ends of the olfactory nerve are distributed. The higher air- breathing Vertebrata are distinguished by the fact that in them this cavity communicates with the pharynx, and by the great surface extension (in a confined area)
. Elementary text-book of zoology. Zoology. 92 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. antenna? in which the gangliated swollen extremities of nerves occur are to be explained as olfactory fibres. In the Vertebrata the olfactory organ usually has the form of a paired pit or cavity placed on the under surface of the head (nasal cavity), on the walls of which the ends of the olfactory nerve are distributed. The higher air- breathing Vertebrata are distinguished by the fact that in them this cavity communicates with the pharynx, and by the great surface extension (in a confined area) of the much-folded olfactory mucous membrane. The fibres of the olfactory nerve terminate in delicate elongated cells, bearing * rods or hairs and placed between the epithelial cells of this mucous membrane. The special sense of taste is confined to the mouth and pharynx. Its function, from what we know of the higher organisms, is to test the quality of fluid sub- stances, and to bring about the special sensation of taste. The presence of this sense can be demonstrated with certainty in the Ver- tebrata, and it is connected with the distribution of a special nerve of taste, the glossopharyngeal, which in man supplies the tip, edges, and root of the tongue and also parts of the soft palate, making these parts capable of the taste sensation. The so-called taste-buds found in special papilla? (papilla? circum- vallata1), with their central fibre-like cells, are explained as the percipient organs of this sense (fig. 89 a, b, c). Taste is, as a rule, connected with the tactile and temperature sensations of the buccal cavity, and also with the olfactory sensations. Finally, special organs of taste appear to be present also in the Mollusc* and Arthropods as a specific sensory epithelium at the entrance to the buccal cavity. In the lower animals the taste and olfactory organs are still less. FIG. 89.—a Transverse section through a circum- vnllate papilla of a calf (after Th.
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
