The oral cirri of Siluroids and the origin of the head in Vertebrates. 395 



The remaining branches belong to the "anterior lower branch" of 

 MCllek. The maxillary nerve (R.mx.) is his branch G' and the 

 coronoid (R. cor.) is his branch 6'". They supply the maxillary and 

 coronoiil tentacles. 



My Ramus raandibularis (R.md.) corresponds to the "deeper 

 finer branch, (I", of the anterior lower branch". Only the sensory 

 part is shown in the figure. It divides into a Ramus mentalis (R.ment.) 

 supplying the fourth or mental tentacle, and a Ramus submandi- 

 bularis {R.siibm.), not specially mentioned by Müller, which supplies 

 the skin in front of and below the anterior lateral piece of the 

 "Zungenbein" of Müller 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 por- 

 tion, and forms a partial wall outside the olfactory organ, being at- 

 tached 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 pre- 

 palatine piece. 



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

 prongs are attached to prefrontal 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 nostrils has been used as a diagnostic of certain groups of 

 the Siluroids (Günther). 



In MoteUa tricirrafa, 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 

 olfactor}- capsule. As such it is known to anatomists as the "nasal 

 labial" or „Xasenflilgelknorpel". 



