. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 170 COMPARATIVE ANATOMY. OLFACTORY ORGAN. The olfactory organ, in its simplest form, consists of a paired, pit-like depression of the integument above the cleft of the mouth. A nerve passes to the base of this pit, and becoming enlarged in the form of a ganglion sends off nerves to the sensory cells (olfactory cells). The latter must be regarded as phylo- genetic derivatives of the end-bulbs of that part of the integu- ment which becomes pushed in to form the primitive olfactory pit ("olfac
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 170 COMPARATIVE ANATOMY. OLFACTORY ORGAN. The olfactory organ, in its simplest form, consists of a paired, pit-like depression of the integument above the cleft of the mouth. A nerve passes to the base of this pit, and becoming enlarged in the form of a ganglion sends off nerves to the sensory cells (olfactory cells). The latter must be regarded as phylo- genetic derivatives of the end-bulbs of that part of the integu- ment which becomes pushed in to form the primitive olfactory pit ("olfactory bulbs"), and therefore come under the same morphological category as the taste-bulbs. At first (that is in Fishes and Urodeles), they are only separated from one another by interstitial epithelial tissue, but from the Anura onwards this tissue gradually disappears in order to allow of an increased surface for the olfactory epithelium. The ciliated cells lying amongst the sensory cells serve to continually renew the outer medium—whether that be water or air—by which the odoriferous particles are conveyed (Fig. 140,-R,^).. FIG. 140.—EPITHELIUM OF THE OLFACTORY Mucous MEMBRANE. Petromyzon planeri; B, of Salamandra atra. R, olfactory cells ; E, interstitial epithelial cells. A, of While the olfactory organs of all the true Fishes exhibit the above-described simple sac-like form, from the Dipnoi onwards they come to communicate with the cavity of the mouth as well as with the exterior. In consequence of this, anterior or external, and posterior or internal nostrils (choanse) can be distin- guished, and as a free passage is thus formed through which the external medium can pass, the olfactory organ takes on an important relation to the respiratory Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the origina
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