. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. 268 COMPARATIVE ANATOMY which communicates with the pharynx by the posterior nostrils, the turbinals arise from the lateral Avails of the chamber and are developed later than the ethmoid turbinals : their skeletal frame- work unites with the maxillary bone, while a less complicated ridge, which may unite with the nasal bone, can usually be recognised. The ethmoturbinals project forwards between the nasotnrlinals and maxillpturbina,ls\ the two last-mentioned no longer possess an olfactory epithelium, and have plainly under
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. 268 COMPARATIVE ANATOMY which communicates with the pharynx by the posterior nostrils, the turbinals arise from the lateral Avails of the chamber and are developed later than the ethmoid turbinals : their skeletal frame- work unites with the maxillary bone, while a less complicated ridge, which may unite with the nasal bone, can usually be recognised. The ethmoturbinals project forwards between the nasotnrlinals and maxillpturbina,ls\ the two last-mentioned no longer possess an olfactory epithelium, and have plainly undergone a change of function in connection with the perception of the warmth and moisture of the inspired air. When well-developed, the maxilloturbinal forms a single or double coil, and may even be more or less branched (Fig. 197); fibres of the maxillary division of the trigeminal supply its mucous membrane. The ethmoturbinals referred to above (endoturbinals) are peculiar to Mammals, as are also certain accessory folds situated laterally to them and also belonging to the ethmoid (Fig. 198): these may c D E. J Fi, transition from latter to single coil, E, F; C, transition from double coil to the dendritic form D. (After Zuckerkandl.) be described as the postero-lateral or ectoturbinals to distinguish them from the endoturbinals and from the antero-lateral maxillo- turbinals and nasoturbinals, which correspond to those of the Sauropsida. The ethmoid turbinals are arranged in a row more or less parallel or obliquely to the palate : their number and relative development varies considerably amongst Mammals and is propor- tionate to the development of the olfactory lobes and sense of smell. In Monotremes two extreme types are seen: Echidna possesses a highly developed and complicated labyrinth of six or more scrolls, while in Ornithorynchus the labyrinth is greatly reduced in adaptation to an aquatic mode of life. A definite type with five endoturbinals occurs in Marsupials, and this
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