357 



The nerve supply to the mental tentacle is by the mental branch 

 of the third division of the Trigeminus. Certain muscles in connection 

 with it remain beneath and between the rami of the lower jaw. 



The last tentacle is the submandibular which I have investigated 

 in Auchenaspis and Silurus. In these two forms it has no connection 

 with a rootpiece but is sustained by a secondary superficial plate of 

 procartilage. It lies below the Meckelian cartilage and from comparison 

 with Myxine I am convinced that the Meckelian bar is the rootpiece 

 of this tentacle. The tentacle is supplied by the submandibular branch 

 of the third division of the Trigeminus and it is worked by inter- 

 maxillary or mylohyoid muscles. Where the tentacle is wanting as 

 in Trichomycterus and Callichthys the submandibular nerve is present 

 precisely as in Myxine. This is the collateral evidence of the former 

 presence of this tentacle in Myxine. 



The Meckelian cartilage in Siluroids demands special attention 

 for it differs markedly from the homologous structure of for example 

 Selachii. Firstly may be noted the presence of the large vertical 

 coronoid process which bears the coronoid piece and tentacle. Secondly 

 in several forms it is very far from reaching symphysis of the jaws, 

 that is to say the mentomeckelian portion is but little developed. 

 This is also the case in Protopterus. In Trichomycterus and Callich- 

 thys the mentomeckelian process is hardly developed at all. In 

 Auchenaspis it reaches about half way from the coronoid process to 

 the symphysis which in these cases is formed solely by the dentary 

 bone. Finally it tapers away behind and in most of the forms examined 

 takes no part in the articulation of the jaws, that being effected 

 by the dermal bones. The mandibular division of the Trigeminus 

 passes internally to the coronoid process, then crossing outside the 

 mentomeckelian process to divide into mental and submandibular 

 branches. 



In form and relations the Meckelian cartilage of Siluroids is 

 strikingly like the anterolateral piece of the „Zungenbein" of Myxine. 

 The other pieces of the latter structure appear to be represented in 

 higher vertebrates by the hypo- and ceratohyals which thus have no 

 connection with gill bars. 



The dermal bones are structures supseradded to a Myxinoid 

 skeleton. 



Thus I have endeavoured to show that the Siluroids in the 

 nervous and skeletal elements of the head present 

 hitherto unrecognised homologies with Myxine. They 

 are of the same type and both can be traced back to an 



