278 Journal of Comparative Neurology. 



sends a twig of the coarse fibers to supply the iith organ of 

 the operculo-mandibular Hne and from this point may be re- 

 garded as containing the r. hyoideus only (Fig. i, hy.). 



Having reached the ventral edge of the operculum, it di- 

 vides, one portion turning caudad and a larger portion cephalad 

 and both containing both coarse and fine fibers. Neither por- 

 tion distributes to cutaneous sense organs of any description ; 

 the distribution shows that the finer fibers are general cutaneous 

 and the coarse fibers motor. The caudal branch of the r. hy- 

 oideus enters the branchiostegal membrane and supplies its skin 

 and muscles behind this point. The cephalic branch runs along 

 the ventral edge of the operculum mesially of the interopercu- 

 lum, ventrally of the cerato-hyal and just dorsally of the line 

 of attachment of the branchiostegal membrane, in which posi- 

 tion it gives off frequent branchlets of coarse and fine fibers 

 which distribute to the skin and muscles of the branchiostegal 

 membrane like the branch last described. It distributes forward 

 in the branchiostegal membrane to its cephalic end. A few 

 fibers are also distributed to the skin covering the cephalic end 

 of the interopercular bone. This nerve (the r. hyoideus) anas- 

 tomoses in front with the branches of the r. mandibularis V for 

 the genio-hyoideus muscle, as in Amia (Allis, '97). 



After the separation of the combined superficial opercular 

 and hyoideus nerve, the next branch given off from the hyo- 

 mandibular trunk is the lateralis branch for pit-organs, the nerve 

 H^ of Cole (Fig. i, H^). This nerve runs laterad and cephalad 

 between two slips of the m. adductor mandibulae and farther 

 cephalad between the ventral one of these slips and the ventral 

 edge of the m. levator arcus palatini. Still farther cephalad, 

 under the eye, this twig bends outward across the dorsal side 

 of the m. adductor mandibulae to reach the skin, in which it 

 distributes in many minute branchlets terminating in pit-organs. 

 These organs lie chiefly in the area of skin under the eye be- 

 tween the infra-orbital and mandibular canals, but also larther 

 back upon the operculum over the opercular canal, and one 

 twig runs cephalad onto the mandible to supply a row of simi- 

 lar organs lying along the mandibular canal for almost its entire 



