An introduction to the systematic zoology and morphology of vertebrate animals / by alexander Macalister.

  • MacAlister, Alexander, 1844-1919.
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: An introduction to the systematic zoology and morphology of vertebrate animals / by alexander Macalister. Source: Wellcome Collection.

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    CHAPTEK IV. Craniota {contimied). The olfactory organ is median and azygos in Marsipo- branclis, double in others, opening externally between the middle and lateral processes of the naso-frontal lobe, and lined with a plaited membrane. In fishes it is a groove, usually crossed by a transverse bridge of skin. Sometimes the membrane is stretched over a papillary eminence {Balistes). In Chimara one opening extends to the angle of the mouth. In Dipnoi and Amphibia the groove lies deeper, between the maxillary arch and the frontal process, and opens into the mouth through the upper lip. In caduci- branchs the hinder opening is bounded by bone. As this canal grows, the true olfactory region becomes by degrees differentiated from it as a diverti- culum from its upper and hinder wall, and in front it becomes complicated by the development of cartilaginous supports, developed either from carti- lages of the ethmoidal region or from the dermis. A horizontal plate extends backwards from the maxillary arch, which becomes the palate, and separates the nasal canals from the mouth. When this extends to the mesethmoid septum it separates one nostril from the other, often leaving long fissures in the nasal floor. The extension of the palate separates the mouth and the nose, leaving the latter to open by choanaj into the post-oral cavity (pharynx), and on the face. Palatine openings may remain permanently between the maxillae and palatine, as in marsupials, or between the maxiUaj and pre- maxillae, as in the incisive canal of Stenson. An anterior mucous diverti- culum from these, which may be lamellated or saccular (and which is supplied by the olfactory, the nasal branch of the fifth, and the naso-palatine and anterior palatine branches of Mechel's ganglion), is called the organ of Jacobson. It is an accessory smelling organ, as if to discern the odour of food when in process of mastication. In the nasal folds of mucous membrane there are formed tm-binal bones (or cartilages, as in tortoises and birds) ; of these, two are connected to the ethmoid (superior and inferior ethmo-turbinals), one is independent, but articulating with the maxilla (maxUlo-turbinal, or inferior spongy bone). This is most largely developed among mammals in the otter and seal, very small in Sirenia, Cetacea, and some marsupials. There is also a sphenoidal turhinal (the bone of Berlin) really connected to the base of the vomer.