ORAL CIRRI OF SILUROIDS AND ORIGIN OF THE HEAD IN VERTEBRATES. 15 



"wall of the orbital region, proceeding forwards, outside the olfactory 

 organ, to reach the nasal tentacle, then dividing into two branches 

 which supply this tentacle. 



The great maxillary stem, taking its exit in front of the hyomandi- 

 bular, proceeds downward and forward to below the eye. Behind the 

 optic nerve it gives off the Ramus palatinus (R. pal.), which runs 

 inwards and downwards, through the anterior portion of the adductor 

 arcus palatini muscle (that part which moves the prepalatine piece and 

 to which it gives motor fibres). Reaching the base of the skull it runs 

 forward alongside the vomer and parallel to the edge of the rostrum, 

 and then reaching the premaxilla it divides into several small twigs. 



Below the eye the great maxillary stem divides into two branches 

 the Bamus maxillaris (R. mx.) and the Ramus mandibulars (R. mcL). 



Almost immediately, the R. maxillaris gives off a Ramus pre- 

 maxillaris (R. pmx^) which runs outside the anterior portion of the 

 adductor arcus palatini, outside the articulating cartilaginous part of 

 the prepalatine piece, above the bony portion, and internal to the 

 anterior cartilaginous part of the prepalatine, Here it runs below the 

 olfactory organ, parallel to the Ramus palatinus, and dividing into fine 

 twigs, is lost in the tissue above the premaxilla at the tip of the snout. 



The Ramus maxillaris runs forward horizontally, above and some- 

 what internal to the coronoid piece, dividing in front into three branches, 

 the innermost of which supplies the skin internally at the upper 

 anterior angle of the mouth, the upper and outermost branch passing 

 downwards in front of the coronoid piece, then dividing into two twigs 

 which supply respectively the anterior faces of the maxillary and 

 coronoid tentacles. The third middle branch runs down, internal to 

 the coronoid piece, and supplies the posterior face of the maxillary 

 tentacle. 



The Ramus mandibularis gives off a Ramus coronoideus (R. cor.) 

 which runs forward, outside and parallel to the R. maxillaris, and 

 turning down, proceeds to the posterior face of the coronoid tentacle. 



The Ramus mandibularis, passing downwards, runs internal to the 

 coronoid process and divides into mental and submandibular nerves, 

 besides giving off motor fibres. The Ramus submandibularis (R. subm.) 

 turns backwards, outside the coronoid process, and supplies the skin 

 below the Meckelian cartilage, while the R. mentalis (R. merit,) is 

 continued forwards to the front of the dentary region. 



