1909.] OLFACTORY ORGAN OF TELEOSTEAN FISHES. 625 



certain bones when the maxillary tentacles are swung forward. 

 This can best be explained by reference to text-fig. 196 (right 

 side). 



The root of the maxillary tentacle is supported and stiffened by 

 the rod of bone that represents the maxilla (MX) which at its 

 proximal end articulates at right-angles with another rod of bone 

 (the palatine bar), that lies in the longitudinal plane and hinges 

 about the middle of its length upon the oviter end of the lateral 

 ethmoid. From the free posterior end of the palatine bar a large 

 muscle (a) fans out towards the floor of the skull and is there 

 attached. Another muscle (the retractor maxillae) takes origin 

 from the floor of the skull to the outer side of a, and running 

 directly forward is inserted by a slender tendon upon the maxilla. 



The outer parts of the accessory nasal sac lie above and in close 

 connection with the palatine bar in front of its hinge point. 



In action the muscle « swings out the anterior end of the 

 palatine bar which in turn rotates the maxilla into a longitudinal 

 position shooting the point of the tentacle forwards. The reverse 

 movements to bring the tentacle to rest result from the action 

 of the retractor tnaxillae. It will be apparent that owing to its 

 close connection with the palatine bar the outer part of the nasal 

 sac will follow its movements. When this bone swings outwards 

 the sac will be dilated, and when it returns to rest, compressed, 

 causing a stream of water alternately to enter the anterior nostril 

 and to be expelled from the posterior or more probably from both 

 nostrils. 



Thus upon structural grounds alone it seems quite clear that 

 when the fish is on the alert it is enabled to bristle its tentacles 

 and sniflf by means of one and the same mechanism. 



In general appearance the rosette is very similar to that found 

 in the Eels, being of considerable length and composed of a large 

 number of laminae set at i-ight-angles to a median raphe. Each 

 lamina (text-fig. 196) has a simple convex free border without a 

 linguiform process. 



Malaptei'urus electricus (text-fig. 197, p. 626). 



The nostrils are situated in much the same position as in Clarices, 

 though relatively closer together. The anterior lies at the end of 

 a short tube the posterior wall of which is prolonged to form a short 

 pointed tentacular process. In a similar way the posterior nostril 

 is guarded in front and at the sides by an upstanding hood-shaped 

 lip. 



The olfactory chamber is a simple flattened circular cavity. 

 The rosette is oval and occupies only the inner half of the chamber 

 leaving the outer half vacant. 



The cavity is thus separable as in Clarias, but to a less degree, 

 into an olfactory chamber lodging the rosette and an accessory 

 sac between the rosette and the posterior nostril. The relations 

 of the vacant part of the cavity to the supj)orting bones of the 



Proc. Zool. Soc— 1909, No. XLIII. 43 



