The oral cirri of Siluroids »nd the origin of the head in Vertebrates. 411 



Addendum. I must confess to not being able to speak with 

 any feeling of certainty concerning the mental tentacle in Siluroids 

 and Cyprinoids. 



The independence of the R. niandibularis externus and tlie ex- 

 istence of the separate block in Auchenaspis may be taken to represent, 

 as an alternative view to the above, a separate external tentacle or 

 Extranieutal. CiCntiieu in the Catalogue of Fishes mentions two pairs 

 of barbels as occurring in a number of Siluroids close to the chin. 

 This is also stated for Cobitidae, but I am in doubt whether the inner 

 smaller process is a real tentacle or only a fold of the skin. It has 

 the form of a tentacle. 



The question may be decided by examination of fuller material 

 or completer literature than has been accessible to me. 



Submandibular Tentacle. 



I have investigated the submandibular tentacle in Auchenaspis 

 and Silnrus. It lies just below the coronoid process, being supported 

 by a subdermal plate of procartilage, which is very large in Auchen- 

 aspis. It has no typical relation with a root piece, but from careful 

 comparison I am convinced that the Meckelian cartilage is the root 

 piece of this tentacle, precisely as in the case of the premaxillary 

 root piece, the prepalatine, and the coronoid block. It is in Myxine 

 that the Meckelian cartilage, or anterolateral piece of the tongue ap- 

 paratus most closely resembles a root piece, a supposition strengthened 

 by the disposition of the nerves. Occurrence of the submandibular 

 tentacle is rare in fish. 



The nerve supply is from the R. subraandibularis which in Silu- 

 roids is given off from the R. niandibularis, just at the point of origin 

 of the coronoid process. The Ramus submandibularis then crosses 

 outside the mentomeckelian process to supply the tentacle. At the 

 branching of the R. mandibularis into R. mentalis and submandibularis, 

 the motor nerves to the muscles , moving the mental and submandi- 

 bular tentacles are given off, A similar disposition of the nerves is 

 described i)y Gaupp in Amphibia. "In Urodela and Reptiha, the 

 principal portion of the Inframaxillary nerve runs in the canal of the 

 lower jaw, as the Ramus alveolaris, forwards at the upper edge of 

 the Meckelian cartilage, but a branch of this Alveolaris inferior runs 

 tlown <ni the outer side of the Meckelian cartilage, and round its 

 lower edge inwards, reaching the inner side after proceeding through 



