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Right Olfactorj' Organ. 



Anterior Nostril {a. nos.). — A small aperture situated 

 on the anterior aspect and almost at the apex of a largish 

 tube. 



Posterior Nostril {p. nos.). — A large aperture only 

 slightly raised above the surface of the body. 



Both nostrils open into a large nasal chamber (??. eh.), 

 the external wall of which is perceptibly thickened, and 

 the internal wall of which is thrown into a vertical series 

 of large folds or olfactory laminse (o. Jam.). These 

 laminse bear the olfactory cells and sensory hairs, to which 

 the olfactory nerve is distributed (?;. olf.), and run in a 

 longitudinal direction. The nasal chamber is therefore 

 the sensory chamber of the nose, and in most fishes is the 

 only one present. There were 9 olfactory laminae in the 

 rig'ht nasal chamber in our sections, bnt the most dorsal 

 and ventral one is very small. 



Into the nasal chamber open the nasal sacs, the walls 

 of which are non-muscular and non-sensory, but contain 

 innumerable goblet cells. They therefore have a secretory 

 function at least. These sacs are as follows : — 



Dorsal nasal sac (//. sac.^). — Opens into the nasal 

 chamber behind and above. Passes forwards and bifur- 

 cates. The inner limb soon terminates, but the outer one 

 passes far forwards, and although it is very narrow from 

 side to side, it is very wide from above downwards. Its 

 true extent therefore does not appear in the figure. 



Antero-Yentral nasal sac (?;. sac.''^). — Has a common 

 opening with the postero-ventral sac into the nasal 

 chamber behind and below. Its outer wall is continued 

 backwards into that of the third sac. Passes far forwards, 

 narrow from above downwards, but wide from side to side, 

 between the mucous membrane of the mouth and the 



