ORAL CIRRI OF SILUROIDS AND ORIGIN OP THE HEAD IN VERTEBRATES. 31 



Certain muscles in Teleostei, considered by Vetter superficial 

 portions of the adductor mandibulae, proceed, not to the lower jaw 

 but, to the maxilla and neighbouring parts. The Adductor tentaculi 

 of Amiurus, described by McMurrich, is one of these. In Cobitidae 

 (Misgurnus) they are very large, labial muscles also being present in 

 correspondence with the presence of the tentacles. Vetter states that 

 they are innervated by a special motor branch of the Trigeminus. 

 They correspond to the Retractores tentaculorum of Myxinoids, and 

 are a further proof of the correctness of the views here maintained. 



Nerve Supply. 



It is impossible in Siluroids to sharply define maxillary and coronoid 

 nerves, inasmuch as many fibres rnnning along with the maxillaris 

 supply the coronoid tentacle. However, there is always a coronoid 

 branch arising from the mandibularis and supplying the posterior face 

 of the coronoid tentacle. Where the coronoid and maxillary tentacles 

 are fused, as in Auchenaspis, the branch is still present in exactly the 

 same relation, and this, indeed, is one of the proofs that the maxillo- 

 coronoid tentacle contains maxillary and coronoid elements. A similar 

 coronoid branch is described as arising from the mandibular nerve in 

 larval Salamanders, by von Plessen and Rabinowicz. 



As to Myxine, the second branch of the Trigeminus divides into 

 maxillary and coronoid branches, apart from motor nerves. They 

 supply maxillary and coronoid tentacles and the skin between them. 



Stannius gives further descriptions of the distribution of the 

 maxillai-is superior in Silurus and Aciqienser, mentioning the pre- 

 maxillary branch in Silurus. He states that the maxillaris superior 

 supplies the upper labial cartilages in Spinax. 



Biichner figures the maxillaris superior in Barbus as an upper 

 branch of the maxillaris inferior. He describes its course and its 

 anastomosis with the premaxillary nerve (his maxillaris superior). The 

 literature of the cranial nerves is immense, but I do not think the 

 facts need further reviewing here. 



Mental Tentacle. 



The mental tentacles of Callichthys are fused at their bases, the 

 fused portion lying medially in front of the symphysis of the dentary 

 bones, Thence the tentacle curves down on each side, and, never 



