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preformed in cartilage, resembling, in this, the mesethmoid processes of the mesethmoid; but, as in 

 the case of the latter processes, the bone is perhaps of perichondrial origin, developed, in that case, in 

 perichondrial membrane, but without the related development of cartilage. The arm of the bone 

 projects antero-latero-ventrally from a relatively small ossification of the side wall of the skull, this 

 ossification lying immediately in front of the orbit and forming the body of tlie bone. From the ventro- 

 mesial corner of the anterior surface of the wing, where the arm and wing join the body of the bone, 

 two ridges start, and diverging slightly run upward and backward to the dorso-posterior edge of the 

 wing. The lateral one of these two ridges terminates in the preocular spine, which lies near the dorsal 

 cnd of the lateral edge of the entire bone. The mesial ridge does not terminate in a spine, but gives 

 Support, along its mesial surface, to the lateral edge of the anterior end of the frontal, a pronounced 

 ridge, formed by the two bones, here appearing on the dorsal surface of the skull. The curved lateral 

 edge of the wing turns sharply forward, at its ventral end, to join the outer end of the arm of the 

 bone, a sharp corner, but not a spine, marking this angle in the edge of the wing. In certain of the 

 Scorpaenidae there is said to here be a short, blunt spine. On the dorso-anterior surface of the wing, 

 lateral to the preocular spinous ridge, there is sometimes an eminence, or short spine, which occupies 

 the Position of a stout process found on the bone of Cottus, that process there giving support to a 

 lateral process of the nasal bone, as will be later described. 



The arm of the ectethmoid is a stout, flat, quadrant-shaped process, which has a slightly curved 

 outer edge presented ventro-laterally, and nearly straight dorsal and mesial edges which are both 

 considerably thickened. The entire arm, in the adult fish, thus looks like two stout processes that 

 arise from a single point, and, diverging, are connected by an intervening portion of thinner bone. 

 In 45 mm specimens the two process-like portions of the arm are of cartilage, enclosed in perichondrial 

 bone, the thinner intervening portion being of bone similar to that that forms the wing of the bone. 

 In tlie adult, one of the process-like portions of the arm lies in a nearly horizontal position, directed 

 laterally and slightly forward. It forms the dorsal edge of the entire arm, and its dorsal surface forms 

 part of the dorsal surface of the entire skull. Its anterior surface is slightly concave and forms the 

 latero-posterior and part of the posterior wall of the nasal pit. Its outer end is considerably thickened 

 and forms a large articular head, capped with cartilage, which is presented latero-ventrally and but 

 slightly anteriorly, and gives articulation to an articular facet on the dorsal edge of the lachrymal. 

 The other process-like portion of the arm forms no part of the boimding walls of the nasal pit. It is 

 directed almost directly ventrally, and its ventral end forms a small elongated articular head, capped 

 with cartilage, which gives articulation to the posterior ethmoid articular surface of the palatine. 

 Between these two articular surfaces, the outer edge of the arm of the ectethmoid is thin, slightly 

 concave, and not capped with cartilage. 



The body of the ectethmoid is an ossification of the ventro-lateral corner of the antorbital 

 process of the chondrocranium, and consists, as the mesethmoid does, of a superficial layer of dense 

 dermo-periehondrial hone, which overlies, but projects every where beyond, a deeper endosteal portion 

 which replaces portions of the cartilage. This body of the bone is of less important dimensions than 

 the part that I have described as its arm. It extends but slightly posterior to the point of origin of 

 that arm, but its anterior portion projects considerably anterior to the arm, is gutter-shaped, and 

 embraces the thin lateral edge of this part of the antorbital cartilage. The rounded lateral surface of 

 this anterior portion of the body of the bone is slightly concave, longitudinally, and a deep rounded 

 angle is thus formed between itself and the concave anterior edge of the horizontal, process-like portion 



