. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. SEA'SE ORGANS. 77 Connected with the nose in all vertebrates above the fishes is a pair of accessory sensory organs, — the organs of Jacobson. They are outpushings of the wall of the olfactory surface, sup- plied by branches of the first and fifth nerves. In the lower amphibia these organs are placed on the medial side of the nasal cavities ; a little higher they are ventral in position ; in the high- est amphibia they have rotated to the lateral side of the olfactory organ. In the amniotes they are either medial or ventral
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. SEA'SE ORGANS. 77 Connected with the nose in all vertebrates above the fishes is a pair of accessory sensory organs, — the organs of Jacobson. They are outpushings of the wall of the olfactory surface, sup- plied by branches of the first and fifth nerves. In the lower amphibia these organs are placed on the medial side of the nasal cavities ; a little higher they are ventral in position ; in the high- est amphibia they have rotated to the lateral side of the olfactory organ. In the amniotes they are either medial or ventral in position. In the lower forms these sacs are connected only. Fig. 83. Section through the nasal region of the Surinam toad, Pipa. c, car- tilage; en, cavum nasale; d, Jacobson's gland and duct; e, ethmoid cartilage; /, frontal bone; /, organ of Jacobson; /, lateral portion of nasal passage; n, nasal bone; nj, branch of olfactory nerve to organ of Jacobson; nn, branches of nasal nerve of trigeminal. with the nasal cavities ; but in the mammals a duct (Stenson's duct) sometimes leads from them into the mouth through the foramina incisiva, between the premaxillary and the palatine processes of the maxillary bones. In many mammals, however, these foramina are closed by membrane, and are vestigial in character. In the mammals for the first time appears an external nose supported by cartilage. In some, like the tapirs and elephants, this organ becomes enormously developed, and forms in the latter the well-known 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 Kingsley, J. S. (John Sterling), 1854-1929. New York, H. Holt and Company
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