— 150 — 



externally and the anterior end of the ectopterygoid internally; tlie three bones being firmly bound 

 together. Posterior to the palatine, and in the same narrow space between the lachrymal and 

 ectopterygoid, a narrow rod of cartilage continues backward and soon expands into a large flat piece 

 of cartilage which lies against the inner surface of that part of the ectopterygoid tliat bears the dermo- 

 ectopterygoid. 



The second infraorbital bone is V-shaped, the hoUow of the V embracing the bluntly pointed 

 anterior end of the third bone of the series. The bind end of the dorsal linib of the V is rounded, and 

 rests upon the externa! surface of the dermo-ectopterygoid. The bind end of the ventral limb is 

 slightly grooved on its inner surface, and this groove receives the anterior end of a pointed anterior 

 process of the quadrate, the two bones being strongly bound together but a slight sliding movement 

 being permitted. The hind end of the second infraorbital, in some specimens, abuts against, while 

 in others it does not quite reach, the anterior end of the ventral limb of the preopercular. The main 

 infraorbital canal enters the: bone at its anterior end, and leaves it at the point of the angle between 

 its two limbs, one sense organ being found in the section of canal so enclosed. On the outer surface 

 of the bone, near the middle of its length, there are two or three spines, these spines lying on the 

 horizontal ridge already described, and that ridge marking the course of the latero-sensory canal 

 in the bone. 



The third infraorbital bone is large and somewhat parallelogrammic in shape. Its ventral 

 end is in contact with the dorsal edge of the ventral limb of the second bone of the series, the ventral 

 half of its anterior edge being in contact with the postero-ventral edge of the dorsal limb of the same 

 bone. The dorsal half of its anterior edge rests upon the outer surface of the dermo-ectopterygoid, 

 a small portion of the latter bone coming to the level of the outer surface of the infraorbital bones, 

 being similarly marked with surface granulations, and appearing as a Prolongation of the dorsal 

 limb of the second infraorbital bone. The hind edge of the third infraorbital bone overlaps internally 

 and rests against the anterior edge of the ventral half of the preopercular. The anterior portion 

 of its dorsal edge is thickened, and bevelled on its inner surface, this bevelied surface having a sliding 

 articulation on that free ventral edge of the ectethmoid that Hes posterior to the posterior palatine 

 articular surface of that bone. The posterior portion of the dorsal edge of the infraorbital bone lies 

 internal to the fourth infraorbital, the latter bone lying in a large depressed region on the external 

 surface of the third bone. The bone is traversed by the main infraorbital canal and lodges two sensory 

 Organs of the hne. 



The fourth infraorbital is a rhomboidal bone traversed by the main infraorbital canal, and 

 lodging one organ of that line. It forms almost the entire ventral margin of the orbit, overlaps 

 externally the third infraorbital, and is bounded both anteriorly and ventrally by that bone. Poste- 

 riorly, it overlaps externally and rests upon the outer surface of a flange of the hyomandibular, its 

 hind edge abutting against the anterior edge of the preopercular, and its dorso-posterior corner being 

 in contact with the fifth bone of the infraorbital series. On its outer surface there is a low, sharp 

 and finely serrated longitudinal ridge, which lies superficial to, or slightly dorsal to the enclosed 

 section of the latero-sensory canal. 



The fifth infraorbital is a triangulär bone that forms the hind margin of the orbit and transmits 

 the main infraorbital canal from the fourth infraorbital to the postfrontal, lodging one organ of the 

 line. Its hind edge rests upon the outer surface of the shank of the hyomandibular, and, in specimens 

 that have been preserved in alcohol, is so firmly attached to that bone that it appears in process 



