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On either side of this median rod of cartilage, tlie dorsal surface of the vomer forms the floor of the 

 anterior half of the rostral Chamber. Posterior to the vomer, the antorbital cartilage expands rapidly, 

 on either side, and then again contracts to a narrow median column whicli is continuous dorsally 

 with the ventral surface of the anterior end of a broad band of cartilage which forms the roof of the 

 interorbital, olfactory Prolongation of the cranial cavity. A diamond-shaped or nearly Square surface 

 of cartilage thus forms the median portion of the post-vomerine portion of the floor of the rostral 

 Chamber, this cartilage being bounded laterally, on either side, by the pedicle of the ectethmoid. 

 There is thus no bone whatever at any point in the median line of the floor of the Chamber. 



The hind wall of the rostral Chamber is fornied by the median column of cartilage just above 

 referred to, and, dorsal to that column, by the broad anterior end of the roofing band of interorbital 

 cartilage. This anterior end of this latter cartilage projects forward slightly beyond the median 

 column, slightly overhangs the hind end of the rostral Chamber, and gives support, on its dorsal 

 surface, to the hind end of the so-called median ethmoid. Immediately beneath this part of the 

 median ethmoid there is, on either side, a slight eminence on the anterior edge of the cartilage, each 

 eminence giving origin to a ligament which runs antero-ventrally and is inserted on the dorsal surface 

 of the maxillary immediately lateral to its ascending process. This ligament is thus the homologue 

 of the ethmo-maxillary ligament of the other fishes of the group, and the little eminence of cartilage 

 from which it has its origin must accordingly be the mesethmoid process; but it is a process of the 

 ethmoid cartilage only, there being no primary bone whatever in any immediate relation to it. On 

 a slight median ridge in the cartilaginous floor of the Chamber, the ventral surface of the rostral glides. 

 There is accordingly, in this fish, no mesethmoid bone. That the median portion of the ethmoid 

 cartilage should remain unossified, and that a median ethmoid bone, of primary origin, should 

 nevertheless be found whoUy external to that cartilage, dorsal to the rostral instead of ventral to it, 

 and dorsal even to the mesethmoid processes of the ethmoid cartilage, is evidently impossible. 



The roof of the rostral Chamber is formed by the single median so-called ethmoid or proseth- 

 moid. This bone suturates posteriorly with the frontals. Laterally, on either side, it suturates, 

 in its posterior half, with the ectethmoid, while in its anterior half it forms the mesial boundary of an 

 elongated nasal opening; which opening lies between this so-called ethmoid and the anterior portion 

 of the ectethmoid, opens directly into the nasal pit and encloses the two nasal apertures. At the 

 anterior end of the opening, the two bounding bones closely approach each other, but do not quite 

 come into contact, a narrow space being left between them, closed antero-ventrally by the lachrymal. 



Slightly antero-mesial to the nasal opening, there is, on the anterior edge of the so-called 

 ethmoid, a short, broad, stout process which projects ventrally and antero-laterally. This process 

 arises from the deeper layers only of the bone, the anterior edge of that superficial portion of the 

 bone that bears the surface markings continuing, uninterruptedly, external to it. The internal surface 

 of the process forms a large flat articular surface which gives a sliding articulation to the flattened 

 anterior end of the maxillary process of the palatine. On its external surface the process gives support 

 to the internal surface of the dorsal edge of the lachrymal, the two bones being strongly but somewhat 

 loosely bound together by fibrous tissue, a slight sliding and oscillating motion, combined, of the 

 lachrymal being permitted. The process thus corresponds, in its relations to the palatine and lachry- 

 mal bones, to the process-hke antero-lateral corner of the nasal bones of Trigla and Peristedion, 

 excepting that here, in Dactylopterus, it is developed as a process-like Prolongation of the ventral 

 layers of the bone, and is interposed between the palatine and lachrymal instead of lying on the 



