. L'anatomie comparée des vertébrés. L'anatomie, les vertébrés ; comparatifs. 266 ANATOMIE COMPARATIVE La structure du nez des chéloniens est très complexe et varié. Dans les chéloniens l'orgue est divisé en deux passages, l'un au-dessus de l'autre, et connecté à l'aide d'une per- foration du septum. La rareté comparative des glandes dans l'organe olfactif des lézards et serpents forme un contraste marqué par rapport à l'état vu dans chéloniens, l'organe nasal est caractérisée par un très grand nombre d'entre eux. L'extension vers le bas et vers l'arrière de l'organe olfactif est la plus marquée en C

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. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. 266 COMPARATIVE ANATOMY The structure of the nose in Chelonians is very complicated and varied. In marine Chelonians the organ is divided into two passages, one above the other, and connected by means of a per- foration of the septum. The comparative paucity of glands in the olfactory organ of Lizards and Snakes forms a marked contrast to the condition seen in Chelonians, the nasal organ of which is characterised by a great abundance of them. The extension downwards and backwards of the olfactory organ is most marked in Crocodiles, in correspondence with the forward growth of the facial region and the formation of the palate; its posterior part thus lies below the brain and base of the skull, the naso-pharyngeal passage being so much elongated that the posterior nostrils open far backwards into the pharynx. Each nasal chamber is divided posteriorly into two superimposed cavities, the upper of which represents the proper olfactory chamber, and is lined by sensory epithelium, while the lower serves as a respiratory passage only. Certain accessory air-chambers are connected with the nasal cavity. A large gland is present between the olfactory chamber and its investing bones, and opens on either side of the nasal septum, posteriorly to the external nostrils, by one or two apertures. As in other Reptiles, there is only a single true turbinal, but externally to it lies a second 0]ir prominence, which may be spoken of as a pseudo-turbinal, and which possibly corre- sponds to the upper turbinal of Birds.. Birds.— In all Birds, as in Lizards, there is an outer chamber lined by stratified epi- thelium, and an olfactory chamber proper, situated above the former. In addition to FIG. 195.—TRANSVERSE a turbinal corresponding to that of Reptiles SECTION THRO UGH THE and usually known as the middle turbinal, RIGHT NASAL CAVITY th j so-called upper turbinal (Fig. 195) : OF A SHRIKE (Lnnuix . -i i ji -11 min

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