ORAL CIRRI OF SILUROIDS AND ORIGIN OF THE HEAD IN VERTEBRATES. 13 



Sensory Tentacular Nerves of Auchenaspis (Fig. 8). 



The trigeminal nerve passes out from the skull, along with the 

 Facial, in front of and below the hyomaudibular articulation, thence 

 passing downwards and forwards below and somewhat internal to the 

 eye, which in Siluroids is small. Just below the optic nerve it divides 

 into two great branches, the upper and internal shortly dividing into 

 palatine (R. Pal.) and maxillary branches. The lower branch slightly 

 further forwards divides into Ramus coronoideus and Ramus mandi- 

 bularis. 



The palatine branch, after separating from the maxillary, passes 

 inwards through an anterior portion of the adductor arcus palatini 

 muscle, that part which stretches from the skull wall in the anterior 

 orbital region to the posterior end of the prepalatine piece, and which 

 moves the maxillo-coronoid barbule. The motor nerves to this muscle 

 run along with the palatine nerve. Reaching the skull wall the pre- 

 palatine nerve passes downwards and forwards, beneath and internal 

 to the preorbital process, lying in fact beneath the lower wall of the 

 passage of the olfactory nerves. Here it runs alongside the edge of the 

 vomer and, reappearing in front of the postorbital process, proceeds, 

 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. 



The maxillary nerve (R. Mx.) runs forward almost horizontally above 

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

 premaxillary branch 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 skin 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 preorbital 

 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 organs to supply the 

 premaxillary region. 



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



