18 H. B. POLLARD. 



in front of and below the anterior lateral piece of the " Zungenbein n 

 of Miiller which I take to be the Meckelian cartilage. 



Comparative Part. 

 Nasal Tentacle. 



The most typical condition of the nasal tentacle is shown in 

 Trichomycterus. The procartilaginous axis expands at its basal portion, 

 and forms a partial wall outside the olfactory organ, being attached to 

 a small bone, one of the terminal antorbitals of the series surrounding 

 the suborbital branch of the lateral line system. This small bone and 

 the base of the tentacle are supported by the prepalatine piece. 



In Clarias the base of the tentacle is bifurcated, and the two prongs 

 are attached to pi'efrontal and antorbital bones, at each side of the 

 posterior of the nasal openings, the tentacle itself rising up in front of 

 the opening behind the small nasal bone. 



The position of the tentacle in relation to the anterior and posterior 

 nostiils has been used as a diagnostic of certain groups of the Siluroids 

 (Giinther). 



In Motella tricirrata, one of the Gadidae, far removed from the 

 Siluroids, the procartilaginous axis of this tentacle bears the anterior 

 tubular opening of the nose, and the basal portion forms the roof of 

 the olfactory chamber. 



In Callichthys though the tentacle is absent there is a procarti- 

 laginous roof to the olfactory chamber, which helps to support the 

 anterior narial aperture and is obviously the basal portion of a tentacle. 



Thus it is seen that when the tentacle is absent yet a basal portion 

 of it may remain and form a support for the wall of the olfactory 

 capsule. As such it is known to anatomists as the " nasal labial " or 

 " Nasenfliigelknorpel." 



According to Sagemehl, such a nasal labial occurs in many Cyprinoids 

 and perhaps in all ; and also in the Characinidae. No doubt on 

 special search it might be found in very many other groups of Teleostei. 



The nasal labial of Selachii has been described in rich detail by 

 Johannes Miiller and Gegenbaur, Many referetices to such structures 

 have been made by Parker, but subsequent investigation has shown 

 his observations to be unfortunately unreliable. 



In many Selachii the nasal labial is fused with the edge of the nasal 



