268 ALUS. [Vol. XVIII. 



canal gives oft a branch which separates at once into two parts. 

 Each of these parts traverses a separate, small, branch canal in 

 the hyomandibular, reaches the outer surface of that bone, enters 

 the preoperculum on its inner surface near the dorsal end of its 

 anterior edge, and then enters the preopercular lateral canal. In 

 that canal the dorsal branch turns upward, but as no indication 

 of a sense organ in relation to it could be found, it is probably 

 not a lateral sensory nerve, notwithstanding its course, position 

 and apparent origin. If it be a lateral sensory nerve its associated 

 organ must have aborted, in advance of the nerve, as would 

 naturally be the case. The other branch turns downward and 

 innervates organ ii of the preoperculo-mandibular line. From 

 the dorsal nerve a small branch was sent backward along the 

 inner surface of the preoperculum. Its ultimate destination could 

 not be determined, but it apparently went to general connective 

 or dermal tissues only. It is, however, to be noted, that, in Aiiiia, 

 in this same region, a branch is sent from the branch that inner- 

 vates organ 14 preoperculo-mandibular to the horizontal cheek 

 line of pit organs (No. 4, p. 616), and that this same branch is 

 apparently found both in Lofa and Esos in the buccalis acces- 

 sorius of those fishes. 



Having issued from the facial canal, onto the external surface 

 of the hyomandibular, the truncus hyoideo-mandibularis runs 

 downward and backward in the groove on the hind edge of that 

 bone, lying in a canal formed by the hind edge of the hyoman- 

 dibular and the anterior edge of the preoperculum. Near the 

 ventral end of the hyomandibular the truncus separates into its 

 two main parts, the ramus hyoideus and the truncus mandibularis. 



The Truncus Mandibularis Facialis, having separated from 

 the ramus hyoideus, turns downward and forward and issues 

 from the canal between the hyomandibular and preoperculum onto 

 the external surface of the former bone. Continuing its course it 

 crosses the external surface of the interspace of cartilage between 

 the adjoining ends of the hyomandibular and symplectic, passes 

 inward through the narrow space between the symplectic in front 

 and the preoperculum and the dorso-posterior process of the quad- 

 rate behind, and reaches the inner surface of the palato-quadrate 

 arch. While on the external surface of the arch it lies internal 



