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teleosts the cartilage is usually first broken down and then replaced by bone developed in relation to 

 periehondrial plates. Be this as it may, the preethmoid of Amia and tbe ascending processes of the 

 vomer of teleosts seem to be developed in relation to the same region of the chondrocranium, and 

 this seems sufficient to establish an homology. 



In Esox, the preethmoid, bone 3 of Huxley's ('72) descriptions, is an ossification of the posterior 

 edge of that abrnptly widened portion of the anterior end of the ethmoid cartilage that Swinnerton 

 ('02) ealls the preethmoid cornu. This ossification, in young specimens of Esox, I find formed of two 

 thin plates of periehondrial bone, united by a thick outer edge of similar appearance, the two plates 

 lying one on the dorsal and the other on the ventral surface of the chondrocranium. In older speci- 

 mens ossification extends into the cartilage, beween the two plates, from the outer thickened edge 

 of the bone. A lateral corner of the anterior end of bone 2 of Huxley's descriptions lies directly upon 

 the dorsal surface of the preethmoid; and on the free, latero-posterior edge of the preethmoid there 

 is a longitudinal articular head, capped with fibro-cartilage, which articulates with a facet on the 

 mesial surface of the anterior end of the palatine. The maxillary bone articulates, by a condylar 

 surface near its anterior end, with a facet on the anterior end of the palatine, the pointed anterior 

 end of the maxillary very nearly, but not quite, reaching the preethmoid and being bound to that bone 

 by tough fibrous tissue. The lateral corner of the anterior end of the single median vomer rests upon 

 the ventral surface of the preethmoid. The preethmoid of Esox, which seems unquestionably the 

 homologue of the preethmoid of Amia, thus has relations to the other bones that are in aecord with 

 the supposition that it finds its homologue in the ascending process of the vomer of Scorpaena, 

 and its manner of development seems intermediate between that of the bone of Amia and that of 

 Scorpaena. The vomer of Esox, as is proper where the preethmoid is an independent bone, con- 

 sists of a ventral plate only, as in Amia, without a vestige of a dorsal limb. 



The only other fishes in which a preethmoid has been described, so far as I can find, are certain 

 of the Cyprinidae, and Belone acus. In the Cyprinidae, Sagemehl ('91) shows a preethmoid (septo- 

 maxillary) lying on either side of the anterior end of the internasal ridge, and forming part of the 

 dorsal surface of the anterior end of the snout. Antero-ventrally it closely approaches the anterior 

 end of the vomer, that bone having no dorsal limb. The preethmoids (septomaxillaries) are said 

 (1. c, p. 510) to each lie upon, or in, a cartilaginous process that gives articulation not only to the 

 palatine but also, through the intermediation of a päd of cartilage, to the maxillary. A fusion of the 

 preethmoids with the vomer would thus certainly here produce the vomer of Scorpaena. 



In the Characinidae the preethmoids are replaced topographically, as well as functionally, 

 by processes of the mesethmoid (Sagemehl, '84b, p. 30), the. vomer reaching, on either side, the base 

 of this process, or even forming part of it. The vomer is said to have acquired pronounced primary 

 relations to the skull, and, in Erythrinus, to even form an important part of the internasal septum. 

 The descriptions and figures are however not definite, and it is impossible to teil whether the preeth- 

 moids are absent or have been absorbed by the mesethmoid or by the vomer. 



In Belone acus, Swinnerton ('02) says there is a preethmoid, and he shows it apj)arently lying 

 on the dorsal surface of the snout, slightly antero-mesial to his prepalatine articular facet and close 

 to the lateral edge of the mesethmoid. Having several specimens of this fish, I have looked for this 

 bone in three of them, but I have wholly failed to find it. 



The frontal, in Belone, has a long, thin, anterior Prolongation which lies closely upon the dorsal 

 surface of the cartilage of the snout, exactly as a similar process of the frontal does in Esox. The 



