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Tlie ECTETHMOID has dermo-perichondrial and primary portions, and resembles, in general 

 shape, the corresponding bone in Trigla. Its posterior surface forms the anterior wall of the orbit. 

 Posteriorly, its superficial component sutuxates with the frontal, while mesially it suturates with 

 the mesethmoid and nasal, extending forward, along the lateral edge of the latter bone, almost and 

 sometimes quite to the hind edge of a small oval nasal incisure in the lateral edge of the skull, This 

 anterior end of the ectethmoid, when it reaches the nasal incisure, forms only a point in the hind 

 wall of that incisure, and the bone has no other bounding relations to the nasal pit. The mesial edge 

 of that part of the ectethmoid that bounds the nasal bone is grooved, and the lateral edge of the 

 related portion of the nasal bone, that edge of the nasal bone here being grooved on its dorsal sur- 

 face, fits into the groove on the ectethmoid; the nasal bone thus appearing, in dorsal views, to here 

 underlie the ectethmoid , while in reality it overlies it. Between the dorsal edge of this portion of the 

 ectethmoid and the dorsal surface of the body of the nasal, there is the long and wide groove above 

 referred to, which groove, although it appears to lie between the two bones, lies largely on the dorsal 

 surface of the nasal bone alone. This groove is roofed, in the recent state, by a thin and tightly 

 stretched drum-head-like membrane, which is pierced by several small holes, the groove lodging 

 he anteriorly-directed second supraorbital primary tube, and the several small holes being the pores 

 by which that tube opens onto the outer surface. Similar drum-head-like membranes, perforated by 

 several small holes, are found associated with nearly all of the primary latero-sensory tubes on the 

 head of the fish, but none of them are so large as this second supraorbital one. 



The ventro-lateral edge of the ectethmoid presents three regions, one of which forms the 

 anterior half of the edge, and the other two its posterior half. The edge of the bone in the posterior 

 one of these three regions is presented ventrally, in a line that extends posteriorly and slightly 

 laterally, and forms the ventral edge of the lateral portion of the orbital surface of the bone. On 

 the outer surface of this part of the bone there is a smooth surface which gives a sliding articulation 

 to a corresponding surface on the inner surface of the dorsal edge of the third infraorbital bone. Imme- 

 diately anterior to this posterior portion of the ventro-lateral edge of the bone, there is a short portion 

 which is thickened and rounded to form an articular edge which articulates with a groove on the 

 dorsal edge of what I shall later describe as the dermo-ectopterygoid. Directly mesial to this articular 

 edge, a groove begins on the ventral surface of the ectethmoid and continues forward along the 

 ventral surface of the lateral edge of the anterior half of the bone. The anterior portion of the lateral 

 edge of the bone, lateral to the groove, is rounded. When the cheek bones Swing inward the groove 

 receives the dorsal edges of the palatine and dermo-ectopterygoid, and limits the swing of the bones. 

 When the cheek bones swing outward the rounded lateral edge of the ectethmoid enters a groove 

 on the dorsal edge of the lachrymal, between it and the palatine, and limits the swing of the bones 

 in that direction. 



A small olfactory canal perforates the antorbital cartilage, mesial to the ectethmoid, lying, 

 in its posterior portion, in the specimens examined, wholly in that cartilage. 



The VOMER caps the end of the thin flat and broad cartilage of the snout, and is wholly 

 without teeth. It has a broad thin and delicate body, which lies partly on the ventral surface of the 

 cartilage of the snout and partly on the ventral surface of the parasphenoid, and two short wide 

 and somewhat stouter ascending processes which lie on the dorsal surface of the cartilage of the 

 snout and come into contact, posteriorly, with the anterior edges of the ventral plates of the nasals. 



