— 180 — 



which doubtless lodges the anterior end of a gristly mandibular core, but this was not investigated 

 in the preparation of my material. On the ventral surface of the dorsal limb of the bone is inserted 

 the strong ligament that has its origin on the internal surfaces of the second and third infraorbital 

 bones. The bone is traversed by the mandibular latero-sensory canal and lodges but two sense organs 

 of the line. 



The articular is a stout bone with a pointed anterior end which fits into the V between the 

 two limbs of the dentary, lying on the dorsal surface of the ventral limb of that bone. On the ventral 

 half of its internal surface is a deep V-shaped groove which receives the hind end of the ventral limb 

 of the dentary. Near the hind end of this groove a canal traverses the bone from its ventral to its 

 dorsal surface, but what it transmits was not determined. The bone is without coronoid process, 

 and nearly its entire hind end is occupied by the articular facet for the quadrate. The bone is tra- 

 versed by the mandibular latero-sensory canal and lodges one organ of that line. 



The angular is a small bone that fits against the ventral surface of the articular, there forming 

 a low, longitudinal and rounded ridge. At about the middle of its length there is a low transverse 

 ridge, the posterior surface of which gives insertion to a ligament that has its origin on a rod-like 

 bone that must represent the interopercular. From the hind end of this little bone a ligament extends 

 posteriorly and has its origin on the externa! surface of the dorsal ossification of the ceratohyal, near 

 its dorso-posterior end; the bone thus being intercalated in the mandibulo-hyoidean ligament, as a 

 part of that ligament, but seeming nevertheless to represent the interopercular. 



The OPERCULAR is, as Gill has said, a flexible subtriangular bone, the external surface of 

 which is covered with scales. 



The SUROPERCULAR is said by Gill to be „almost membranous, mostly concealed", and 

 to lie internal to the ventral end of the opercular. I find it as a relatively stout and curved bone, 

 the dorsal end of which lies internal to the ventral end of the opercular, while the ventral end 

 curves forward and lies against the internal surface of the preopercular; this latter end of the bone 

 being directed toward but widely separated from the hind end of the interopercular. In Figure 71, 

 which alone shows these bones, the line separating the subopercular and opercular has been omitted. 



The INTEROPERCULAR is apparently represented, as Gill has stated and as just above 

 described by me, by a rod-like bone intercalated in the mandibulo-hyoidean ligament. 



4. LATERO-SENSORY CANALS. 



The main infraorbital canal begins at the dorsal edge of the lachrymal, directly antero-ventral 

 to the anterior end of the large nasal opening between the nasal and ectethmoid bones, there lying 

 directly opposite and close to the anterior opening of the supraorbital canal. It runs at first ventro- 

 laterally, then turns sharply backward at a right angle, and so continues in a nearly horizontal 

 position until it has traversed the lachrymal and the anterior two-thirds of the second infraorbital 

 bone. There it turns sharply upward and forward, at an acute angle, and curving backward and 

 upward borders the hind edge of the orbit, traversing the second, third, and fourth infraorbital bones. 

 At the anterior end of the horizontal part of its course, it sends a short branching tubule forward 

 in the lachrymal, and at the hind end of this part of its course, it sends a long branching tubule 

 directly backward nearly to the postero-ventral corner of the second infraorbital bone. Numerous 

 other tubules arise from the canal in this part of its course, some of them being simple tubes while 



