SMELL. ■ • XXXVll 



depressions is formed of a fibrous membrane, which in its turn lies upon a 

 cartilaginous or more frequently an osseous basis, termed the turbinal bones. 



The appearance of these openings or nostrils in bony or teleostean fishes 

 is various. There are generally two apertm-es on the, upper. surface, side, or 

 front edge of the snout leading to each olfactory sac, the one often tubular, 

 the other oval and patulous, while between them a bridge of integument or 

 even a wide interspace exists, and attached to their edge is often a valve which 

 protects one or both of the orifices. The anterior nostril is most frequently 

 tubular and contractile, the posterior open, while internally the two com- 

 municate one with the other. In a few forms only one opening is present 

 for each sac. In some eels and a few other bony fishes we- find a nasal orifice 

 on the inner side of the upper lip. 



In the Plagiostomes the nasal depressions are very large, and a mem- 

 branous or cartilaginous opercle -is present, by which they may be closed : 

 they open on the under surface of the face. The membrane Hning them is 

 exceedingly vascular, and provided with, cryprts which secrete mucus ; the 

 membrane is sometimes' folded, and on these folds are occasionally stellated 

 ridges, in order to increase the extent of the surface. As the nasal cartilages 

 have their proper muscles, it has been concluded "that these fishes scent as 

 well as smell, i.e. actively search for odoriferous impressions by rapidly 

 changing the current of water through the olfactory sac" (Owen, i, p. 329). 



In the Cyclostomata we find an unpaired or single nasal aperture, situated. 

 on the upper surface of the head. In one species, " the Myxine," a com- 

 munication with the p&late exists in the form of a naso-palatine canal, which 

 opens backwards oh the palate, where it is furnished with a valve j whereas 

 in the Petromyzon the nasal duct terminates in- a blind pouch, without per- 

 forating the palate. In Amphioxus the organ of smell is likewise single, in 

 the form of a simple depression, placed rather on the left side, and which 

 ends in a small, dilated, blind pouch, resting upon the central axis of the 

 ■ nervous system. 



For the supply of these organs we have the olfactory nerve, which arises 

 alone from the rudimentary hemisphere of the brain, and having dilated, 

 perforates the anterior portion of the skull, where it corresponds with the 

 cribriform plate of the ethmoid bone, and immediately divides and subdivides 

 upon the radiating laminis' here covered with the pituitary nasal membrane. 

 A branch of the fifth pair or one for sensation likewise goes as an accessory 

 nerve to the organs of smell. 



That odour may exist in water is evident, and I have been informed by 

 a gentleman who kept tame otters in India, that he has seen them hunt 

 along the bottom of a narrow and clear stream, follo.wing the trail of a fish 

 as unerringly as a hound works on land. Whether this odour is from the 

 fish itself or due to its excretions may be questioned. 



