. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. OLFACTORY ORGAN 199 two portions, an anterior and a posterior (Figs. 157, B, and 158), by a fold of skin. The nostril often lies at the summit of a longer or shorter tube, lined with ciliated cells, and the distance between the anterior and the posterior aperture varies greatly, according to the width of the fold of skin which separates them. The mucous membrane of the nasal organ of Fishes is always raised up into a more or less complicated system of folds, which may have a transverse, radial, rosette-like, or longitu
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. OLFACTORY ORGAN 199 two portions, an anterior and a posterior (Figs. 157, B, and 158), by a fold of skin. The nostril often lies at the summit of a longer or shorter tube, lined with ciliated cells, and the distance between the anterior and the posterior aperture varies greatly, according to the width of the fold of skin which separates them. The mucous membrane of the nasal organ of Fishes is always raised up into a more or less complicated system of folds, which may have a transverse, radial, rosette-like, or longitudinal arrange-. E80 Fig. 158.—Lateral View of the Head of Murima helena. VR and HB, anterior and posterior tubes of the external nostrils ; A, eye ; HSO, integumentary sense-organs. ment, and which are supplied by the branches of the olfactory nerve. The olfactory organ of Polypterus is more highly developed and compli- cated than that of any other Fish. In certam representatives of the Pleoto- gnathi and Gymnodontes amongst the Teleostei, on the other hand, the organ shows various stages of degeneration. Dipnoi.— A nasal skeleton well differentiated from the skull proper is met with for the first time in Dipnoans. In Protopterus it consists of a cartilaginous trellis-work enclosing each olfactory sac and united with its fellow in the median line by a solid septum : the floor is formed mainly by the pterygopalatine and by con- nective tissue. The mucous membrane is raised into numerous transverse folds connected with a longitudinal fold, and the olfac- tory organ in general most nearly resembles that of Elasmobranchs,. 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 original Wiedersheim, Robert, 1848-1923; Parker, William Newton, 1857-1923. London, Macmillan
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