142 ALUS. [Vol. XVIII. 



and downward across the external surface of the ventral end of 

 the former, there is a narj-ow slit, which transmits the truncus 

 mandibularis facialis, from the groove on the dorso-posterior sur- 

 face of the hyomandibular to the external surface of the hyoman- 

 dibulo-symplectic. In the groove on the dorso-posterior sur- 

 face of the hyomandibular, somewhat above the middle point of 

 the bone, a canal leads forward and upward into the bone itself, 

 and issues on its mesial surface near the ventral edge of the base 

 of the anterior articular process. This canal transmits the truncus 

 hyoideo-mandibularis facialis from the internal surface of the 

 hyomandibular to the groove on its dorso-posterior edge. The 

 facial nerve thus has, in a part of its course, much the same rela- 

 tions to the hyomandibular that the branchial nerves have to the 

 proximal elements of their respective arches. 



The ramus hyoideus facialis leaves the truncus hyoideo-man- 

 dibularis near the ventral end of the groove on the dorso-posterior 

 surface of the hyomandibular, and, passing backward and inward 

 between the adjoining edges of the hyomandibular and preoper- 

 culum, issues on the internal surface of the latter bone slightly 

 dorsal to the dorsal end of the epihyal. 



From the canal that transmits the facial nerve through the hyo- 

 mandibular, near its dorso-internal end, a small canal leads back- 

 ward and laterally in the bone. It soon separate^ into two parts 

 both of which traverse the bone and issue in the groove on its 

 dorso-posterior surface, one at the level of the dorsal edge and 

 the other at the level of the ventral edge of the base of the 

 opercular process (Fig. 36). The openings of both of these 

 canals lie internal to the preoperculum, between it and the hyoman- 

 dibular, and they both give passage to branches of the facialis 

 destined to supply the one or more lateral sense organs that lie in 

 the dorsal part of the canal that traverses the preoperculum. 



The ventral end of the hyomandibular is united by a small in- 

 terspace of cartilage with the dorsal end of the symplectic. Ad- 

 joining the ventral end of the hyomandibular a part of this carti- 

 lage seems to belong much more to that bone than to the rest of 

 the interspace, the histological condition being such that the hyo- 

 mandibular could almost always be separated with a rounded carti- 

 laginous end attached to it, this end fitting into a corresponding 



