. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 454 Coinparatwe Animal Physiology in the superior part of the nasal cavity. In deer the area is much greater. During normal respiration of man most of the air does not pass directly over the olfactory organ, but this is supplied with air (and odors) primarily by eddy currents (Fig. 146). The secluded position of the olfactory epithelium seems to be important in preventing desiccation of the protoplasmic processes of the olfactory cells. Hou'cver, in sniffing, the volume of air passing the olfactory organ is grea
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 454 Coinparatwe Animal Physiology in the superior part of the nasal cavity. In deer the area is much greater. During normal respiration of man most of the air does not pass directly over the olfactory organ, but this is supplied with air (and odors) primarily by eddy currents (Fig. 146). The secluded position of the olfactory epithelium seems to be important in preventing desiccation of the protoplasmic processes of the olfactory cells. Hou'cver, in sniffing, the volume of air passing the olfactory organ is greatly increased. In dogs more of the air passes directly over the olfactory epithelium. Jacobson's organ or the naso-vomerine organ, located in the nasal septum, is well developed in some fishes and reptiles and is believed to function as an accessory olfactory organ. Histologically, the olfactory epithelium (Fig. 147) consists of the olfac- tory receptors (primary neurones) embedded in columnar epithelial cells, some of which contain a yellowish-brown pigment and give the organ a. Fig. 146. Diagram of the right nasal cavity of man, showing the direction of air flow. Eddy currents around the superior concha are created by sniffing and bring the inspired air into contact with the olfactory epithelium. After Evans"' from ; yellowish appearance macroscopically. The primary neurones are bijx)lar, with the dendrite forming the receptor proper and the cell body performing the function of "ganglion cells" in supplying the fibers (unmyelinated) of the olfactory nerve. 1 he olfactory epithelium also contains free nerve end- ings of the trigeminal ner\'e which function as part of the common chemical sense receptor. The olfactory organ is the simplest sense organ of the body and is also very sensitive. Stimulation probably occurs through the hairlike processes, and the sense cell, serving as both receptor and conductor, trans- mits this to the brain. Compared with
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