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trigeminus ganglion and issues through the trigeminus opening of the trigemino-facialis Chamber, 

 this being the second trigeminus bündle to join the facialis, the other bündle issuing through 

 the facialis opening of the trigemino-facialis chamber, joining the nervus facialis internal to 

 the hyomandibular, and going largely, if not entirely, to the ramus hyoideus. The ramus 

 mandibularis, thus formed, after giving off certain branches, passes downward and inward through 

 a large opening between the hind edge of the symplectic and the anterior edge of the web of bone 

 that spans the angle between the two limbs of the preopercular, this opening being the regulär foramen 

 for the ramus mandibularis externus. Certain fibers other than lateralis ones form part of the nerve 

 that passes through the foramen, but whether they are partly communis or wholly general cutaneous 

 could not be determined in my material. It is, however, certain that, in this fish, no important 

 bündle of communis fibers passes inward anterior to the symplectic, where the ramus mandibularis 

 internus should normally pass, and, in my material, I could not there find an opening that I could 

 certainly call a foramen and not an artifact. From the facialis canal, near its internal opening, a canal 

 leads backward in the hyomandibular, as usual, opens on its external surface near its hind edge and 

 immediately ventral to the opercular process, and transmits a nerve containing lateralis and general 

 cutaneous fibers destined to innervate the dorsal two organs of the preopercular canal and tissues 

 on the outer surface of the opercular. 



The ramus hyoideus facialis thus never reaches the external surface of the hyomandibular, 

 and it accordingly here has relations to that bone that might be taken to indicate that it was in process 

 of cutting through the bone from its outer to its inner surface; but this is certainly not the case, the 

 condition being in some way related to the development of that tall ridge cn the external surface of 

 the bone that gives support to the preopercular. This ridge lies, in certain fishes (Scorpaena, Trigla etc.), 

 posterior to the external opening of the facialis canal through the hyomandibular, while in others 

 (Scomber) it lies anterior to that opening. If, in one of these latter fishes, the ridge were to be pushed 

 backward into the position, relative to the shank of the bone, that it has in Dactylopterus, it would 

 probably pass over the ramus mandibularis, held in position by its lower foramen, but would push 

 the ramus hyoideus downward and backward onto what would be morphologically a part of the 

 posterior surface of the bone, though appearing as a part of its internal surface. An intermediate 

 stage in such a process is shown in Gasterosteus, where, according to Swinnerton ('02, p. 544), „the 

 hyomandibular nerve foramen occupies the same position as it did in the last stage, but externally 

 at first sight it seems to have disappeared; in reality it has been carried to the ventral edge [of the 

 hyomandibular] by overgrowth of bone". 



The distal end of that slightly thickened portion of the hyomandibular that represents the 

 shank of the bone is in synchondrosis with the usual interspace of cartilage, that cartilage being 

 bounded anteriorly by the metapterygoid, antero-ventrally by the symplectic, and posteriorly by 

 the web of bone that fills the angle between the two limbs of the preopercular. The interspace gives 

 articulation, on its internal surface, to a relatively long and important interhyal. Immediately 

 dorsal to this interspace of cartilage, the anterior edge of the hyomandibular is in contact with and 

 firmly bound to the dorso-posterior corner of the metapterygoid, and between the two bones and 

 the interspace of cartilage there is a relatively large foramen which transmits the arteria hyoidea. 



The SYMPLECTIC is broad and flat, and lies in the line, prolonged, of the shank of the hyo- 

 mandibular. Its ventral end overlaps the dorsal edge of the quadrate, and lies in a slight depression 

 on the internal surface of that bone. The anterior edge of the bone is bounded externally by the 



Zoologica. Heft 57. 23 



