Tlie oral cirri of Siluroids and the origin of the head in Vertebrates. 391 



ceeds, parallel to the edge of the rostrum and beneath the olfactory 

 organ, to the end of the snout where, on reaching the premaxilla, it 

 divides into several small twigs. 



Tiie maxillary nerve {li.Mx) runs forward almost horizontally 

 above the edge of the posterior part of the prepalatine piece, giving 

 00" the premaxillary l)ranch and passing just outside the postorbital 

 process. It then takes a long course forward between the anterior 

 part of the prepalatine and the coronoid piece , giving off above a 

 small branch to the skin and, below, another branch which supplies 

 the skill at the base of the maxillo-coronoid tentacle. 



The main portion turns outward and supplies the anterior face 

 of the maxillo-coronoid tentacle. 



The premaxillary branch (R.pmx.) passes external to the pre- 

 orbital process, crossing over the prepalatine piece to lie internal to 

 this piece, runs forward parallel to the edge of the rostrum, and 

 divides into twigs which run beneath and outside the olfactory organ 

 to supply the premaxillary region. 



The coronoid branch {R.cor.) is given off from the mandibular 

 nerve and passes forward parallel to and just outside and below the 

 maxillary nerve. It turns outward, still parallel to the maxillary 

 nerve, and supplies the posterior face of the maxillo-coronoid tentacle. 



The mandibular nerve {R.md.) passes downwards and forwards 

 and, some little distance behind the coronoid process, it divides into 

 Ramus mandibularis externus and R. md. internus 



The R. md. externus passes outside the coronoid process forwards 

 and downwards outside the mento-meckelian process, and reaches the 

 posterior edge of the mental piece (the large block of procartilage in 

 the lower lip). Here it divides into a number of twigs which supply 

 the fold of skin below and behind this piece. 



The R. md. interims passes inside the coronoid process and 

 divides into two branches which 1 name mental and submandibular. 

 The mental branch (R. ment.) passes forwards, outside and below the 

 mento-meckelian process, internal to the R. md. externus. Proceeding 

 horizontally forwards, it crosses internally the block of procartilage of the 

 lower lip and, reaching the mental tentacle, passes down it, dividing 

 then into two branches, which supply the anterior and posterior 

 aspects of the tentacle. 



The submandibular branch (R.subm.), after parting from the 

 mental , proceeds down outside the mento-meckelian process to the 

 submandibular tentacle, dividing into two branches, which supply the 

 anterior and posterior faces of the tentacle. 



