330 ANATOMY OF VERTEBRATES. 



search for odoriferous impressions by rapidly changing the current 

 of water through the olfactory sac. 1 



The Protopteri show no outward signs of olfactory organs : the 

 thick upper lip must be raised to bring the plicated sac, with its 

 two remote orifices, into view. In Amphiuma the external nostrils 

 are minute, approximate, and near the end of the snout. In the 

 Siren and Axolotl the external nostril is conspicuous on each 

 side the snout: the internal one opens outside the series of 

 ptervgo-vomerine teeth. In the Siren the maxillary does not 

 extend back so as to divide the internal nostril from the inner or 

 under part of the lip : in the Axolotl it is so extended, and the 

 opening is situated between the maxillary and palatine series of 

 teeth. In these, as in the Proteus, the olfactory membrane is 

 plicated at right angles to a longitudinal seam. In the Newts 

 and Salamanders the olfactory membrane is smooth, and lines an 

 oval cavity with an external nostril and a palatal one, the former 

 defended by a little fold of skin. 



In tailless Batrachia the external nostril has an inferior flap, 

 endowed with a slight movement : the palatal is widely open, 

 between the palatine and maxillary bones, near the fore part of 

 the mouth. The olfactory membrane is not augmented by any 

 folds or prominences. In the Pipa it presents a cylindrical form, 

 and its outer opening is much nearer that of the opposite side 

 than in other Anoura. In Ophidia the external nostrils are 

 double ; the internal nostril is single and median : the bone and 

 gristle supporting the olfactory sac make some prominences in it ; 

 the pituitary membrane is almost black in some Colubers. In 

 Aw/rds, and other snake-like Lacertians, the palatal nostrils open 

 separately. 



In the Iguana a single broad turbinal cartilage extends into the 

 olfactory cavity from the outer side, terminating below in two 

 tuberosities. The meatus extends at first longitudinally back- 

 ward, then bends downward to open upon the palate between the 

 anterior maxillary and the pterygoid teeth. The turbinal projects, 

 with slight modifications of proportion and form in the nasal 

 cavity of other Lacertians. The external nostrils offer varieties 

 of relative size, shape, and position, seldom receding far from the 

 muzzle in existing species. In the extinct Saurians of marine 

 habits, Ichthyosaurus and Plesiosaurus, the external nostrils 

 opened near the orbits, at a distance from the muzzle. In Chelonia 



1 'Is the mode of smelling in Fishes similar to tasting in other animals? Or is 

 the air contained in water impregnated with the odoriferous parts, and is it this air 

 which the tish smells? ' — John Hunter, in xx. vol. iii. p. 88. 



