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Summary.

  • 1
    The nasal organs of Sphenodon and lizards are considerably modified by the mode of life, which in turn influences the form of the nasal capsule.
  • 2
    The anterior chamber functions as a filter in preventing foreign bodies from entering the respiratory tract. It is well marked in terrestrial forms that are specialized for a deserticolous existence, but it is very reduced in arboreal forms.
  • 3
    The lateral nasal gland passes its mucoid secretion into the anterior chamber, and serves to bind to the epithelium any small particles that have been inhaled. It is well developed in deserticolous and fossorial forms, but reduced in arboreal and semi-aquatic lizards.
  • 4
    The olfactory chamber is well developed in terrestrial forms, but reduced in arboreal ones. Conchal formation is dependent upon orbital expansion.
  • 5
    Jacobson's organ is a specialization of ground-living lizards, and is reduced in arboreal forms. Stimulating particles are deposited by the tongue onto the choanal fold. They are carried by means of ciliary currents into, and along a continuous stream of lachrymal fluid passing to the organ. Some lizards by the development of deeply forked tongues deposit the particles directly into the organ.
  • 6
    The definitive nasal capsule is formed by the fusion of two distinct morphological elements. There is a medial rostral process which belongs to the cranium, and consists of the nasal septum, dorsal plate, and sphenoethmoidal commissure. The lateral capsular element, which is a true sensory capsule, is divisible into parietotectal, paranasal, paraseptal, and ectochoanal cartilages.
  • 7
    The rostral elements arise earlier in the embryo than do the capsular elements, and are distinguished in the adult by the relations of the profundus nerve, which lies ventral to the rostral element and dorsal to the capsular element. The line of union is taken from the points of entry and exit of this nerve, and the position of certain fenestrae.
  • 8
    The fenestrae are due in the first place to weak development of the dorsal plate, and secondarily follow weak capsular development. In the case of fenestrae superior it follows weak parietotectal cartilage development, while fenestrae lateralis appears where there is marked conchal formation.
  • 9
    The dorsal plate forms most of the roof of the capsule, and with the spheno-ethmoidal commissure encloses the cranial olfactory foramen.
  • 10
    The parietotectal cartilage is related to the fenestra narina and encapsulates the anterior chamber, on which it is dependent for its form. The paranasal cartilage encapsulates the olfactory chamber and gives rise to the lamina transversalis anterior, concha, planum antorbitale, and posterior maxillary process. The ectochoanal cartilage has become secondarily associated in lizards with the functioning of Jacobson's organ.