328 PHILOSOPHY OF ZOOLOGY. 



motion. This motion, however, in living fishes, can seldom 

 be perceived. 



Proceeding to the examination of the inside of the nos- 

 tril, we may observe, that, in the sharks, skates, and eels, 

 the nasal laminae are placed parallel to each other, on both 

 sides of a large lamina, which extends from one end of the 

 fossa to the other, and consists of folds of the pituitary 

 membrane. In general, in the other fishes, whether carti- 

 laginous or osseous, the laminae proceed like radii from an 

 elevated and round tubercle, The pituitary membrane, in 

 some fishes, as in the pike, is furnished with reticular rami- 

 fications of black vessels, but in the greater number of fishes 

 these vessels are red. Between these, are situated some; 

 small papillae, which pour out a thick mucilage. 



The Olfactory Nerves, at their origin, form swellings or 

 knots, so large as frequently to have been mistaken for the 

 real brain. These tubercles in skates and sharks are united 

 into one homogeneous medullary mass, from each of the 

 lateral parts of which the olfactory nerves arise. In the 

 species of the genera Pleuronectes, Clupea, Esox, Perca, 

 and Salmo, there are two pair of tubercles, the anterior of 

 which is smaller than the other. 



In the cartilaginous fishes, as the skate and shark, the 

 olfactory nerve is very soft. It is, in them, a bulb which 

 passes obliquely forward toward the nares, which are at a 

 greater or less distance from the brain ? according to the 

 species. The spinous fishes have the olfactory nerve very 

 long and slender. In those which have the snout elonga- 

 ted, this nerve is received into a cartilaginous tube. In 

 those with short snouts, the nerve is surrounded by a fine 

 membrane only, whiqh appears to be the same as that which 

 contains the fat or oily humour that covers the brain. In 

 the haddock, and some other fishes, the olfactory nerve, in 

 its course from the brain to the nose, passes through a cine- 



