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the hyomandibular in the angle between tlie opercular arm and the shank of the bone, and the other 

 close to the hind edge of the web of bone that fills the space between the same two arms of the bone. 

 This second and branching canal transmits the two branches of a nerve that supplies the two dorsal 

 latero-sensory Organs of the preopercular canal. 



The ramus hyoideus separates from the truncus hyoideo-mandibularis as that nerve reaches 

 the external surface of the hyomandibular, passes downward and backward through a small passage 

 between the hind edge of the hyomandibular and the anterior edge of the preopercular, and so 

 reaches the internal surface of the latter bone. 



SYMPLECTIC. 



The symplectic is a slender curved bone, the dorsal two-fifths of which lie along the hind edge 

 of the cartilage that separates the metapterygoid and quadrate, while the ventral three-fifths lie 

 in the symplectic groove on the internal surface of the quadrate. The ventral end of the bone is tipped 

 with cartilage. Its dorsal end is bounded by the interspace of cartilage that lies between itself and 

 the hyomandibular. This interspace of cartilage is in close contact with the hind edge of the palato- 

 quadrate cartilage, but is not continuous with that cartilage. A part of the hind edge of the inter- 

 space of cartilage is overlapped externally by a thin web of bone on the anterior edge of the preoper- 

 cular, near the middle of its length, and the hind edge of this part of the cartilage bears the articular 

 facet for the proximal end of the interhyal. Between the hind edge of the dorsal portion of the sym- 

 plectic, anteriorly, and the anterior edges of the preopercular and the posterior process of the quad- 

 rate posteriorly, there is a long oval space which transmits the ramus mandibularis externus facialis 

 and the arteria hyoidea. Along the anterior edge of the symplectic, between it and the hind edge 

 of the dorsal portion of the body of the quadrate, there is a small opening which transmits the ramus 

 mandibularis internus facialis. 



PREOPERCULAR. 



The preopercular is a curved bone, traversed its füll length by the preopercular latero-sensory 

 canal. It has, on its hind edge, five so-called spines, the two ventral ones being blunt or pointed 

 eminences, rather than spines. The dorsal spine is by far the longest and is always double, a small 

 spine, almost completely fused with it, arising on the external surface of its base. At the ventral 

 edge of the base of this small spine, and hence on the external surface of the base of the large spine, 

 there is the opening of a primary latero-sensory tube; and similar openings are found at the ventral 

 edges of each of the three next distal spines. The fifth spine lies at the distal end of the bone, is an 

 eminence rather than a spine, and immediately distal to it there is a primary tube which arises from 

 the sensory canal as it passes from the preopercular into the mandible. The spines, thus here, as 

 on the lachrymal, have definite relations to the primary tubes of the latero-sensory system; but 

 there is not a spine for every tube, for dorsal to the most dorsal spine there is, in the preopercular, 

 still another opening of the latero-sensory canal, but without related spine. The bone lodges six 

 latero-sensory organs, one between each two adjoining tubes. 



At the middle of the anterior edge of the preopercular, spanning the hollow of the curve of 

 the bone, there is a thin web of bone which bears, on its internal surface, a small cup-like depresion, 

 this depression reeeiving the lateral surface of the proximal articular head of the interhyal and to 

 that extent forming part of the articular cup for that element. Lateral to this web of bone, or 



