— 90 — 



lateralis ones, and they are said to have been definitely traced to certain opercular pit organs. In 

 Pleuronectes, Cole and Johnstone ('Ol, p. 132) also find the nerve a purely lateralis one, its terminal 

 branches supplying an opercular line of pit organs. 



Having given off this small branch the main truncus, in Scorpaena and Lepidotrigla, traverses 

 the facialis canal in the hyomandibular and issues on the external surface of the shank of that bone. 

 There it separates into its two parts, the ramus hyoideus and truncus mandibularis, the latter of which 

 soon separates into the rami mandibularis externus and internus. The ramus hyoideus runs downward 

 and backward through the opening between the hyomandibular and the preopercular and so reaches 

 the hyoid arch, its further course not being traced. The rami mandibularis externus and internus 

 run downward and forward across the hyomandibulo-symplectic interspace of cartilage, and then 

 pass, respectively, through the openings on the posterior and anterior side of the symplectic, as 

 already fuUy described, and so reach the inner surface of the palato-quadrate apparatus and then 

 the mandible. The externus sends branches, as usual, to the latero-sensory organs of the preoper- 

 culo-mandibular line, and certain branches also to the general tissues, the nerve thus not being a 

 simple latero-sensory nerve. The internus goes to the inner surface of the mandible, its special distri- 

 bution and relations to the other nerves not being investigated. Whether it contains communis fibers, 

 and those fibers only, as in Menidia, could not be determined, but, whatever its composition may 

 be, it is a true ramus mandibularis internus as that nerve is defined by Stannius. Herrick ('99, p. 171) 

 takes the position, and it may be correct, that a nerve can not be a mandibularis internus unless 

 it contains communis fibers; and the inference is that it must contain those fibers alone, for he says 

 that the nerve is absent in Gadus notwithstanding that both Stannius and Cole describe a nerve in 

 that fish that is said to have the topographical position of an internus. Neither Stannius' nor Cole's 

 descriptions of the course of the nerve being very definite, I have had the nerve looked for in dis- 

 sections of Gadus merlangus, but it could not be found; which would seem to confirm Herrick's con- 

 clusion that the nerve, when present, conta,ins communis fibers only. 



In Dactylopterus the truncus hyoideo-mandibularis facialis does not traverse a single canal 

 in the hyomandibular and issue on the external surface of that bone, as it does in Scorpaena, Cottus, 

 Trigla and Lepidotrigla. When it reaches the internal surface of the hyomandibular the nerve, in 

 Dactylopterus, separates into its two portions, the ramus hyoideus and the truncus mandibularis, 

 the latter of which alone traverses the facialis canal through the bone and issues on its external sur- 

 face. The ramus hyoideus simply passes beneath a bridge of bone on the internal surface of the 

 hyomandibular and reappears on the internal surface of that bone. This will be further discussed 

 when describing the bones in this fish. From the truncus mandibularis, as it enters its canal in the 

 hyomandibular, a lateralis branch, accompanied by what are apparently whoUy general cutaneous 

 fibers, passes backward through a small branch canal in the bone, this nerve supplying the two dorsal 

 organs of the preopercular canal and the tissues on the outer surface of the opercular. The truncus 

 mandibularis contains communis fibers and is joined, after it reaches the outer surface of the hyo- 

 mandibular, and as already stated, by the communicating general cutaneous branch that issues 

 through the trigeminus opening of the trigemino-facialis Chamber. After being joined by this com- 

 municating branch, the entire truncus mandibularis passes to the internal surface of the palato- 

 quadrate through an opening that lies posterior to the symplectic, no evident branch passing in- 

 ward anterior to that bone. There is thus no evident ramus mandibularis internus in this fish. The 

 mandibularis externus, after it reaches the internal surface of the palato-quadrate, certainly con- 



