— 18 — 



seem as if it might be partly of perichondrial origin, this perichondrial portion of the bone lying directly 

 lipon the iinderlying cartilage but not yet having acquired endosteal relations to it. In certain spe- 

 ciinens, as seen in Figure 10, a bit of cartilage is enclosed in the vomer, near its anterior end, this 

 seeming to indicate that this part of the bone is of perichondrial origin and has surrounded and iso- 

 lated a bit of the chondrocranium. In sections of young specimens the ascending processes of the 

 bone lie closely against the cartilage but are separated from it by a line of tissue, and this tissue is 

 certainly not a simple perichondrial membrane. Just what it is, I liave not sufficient histological 

 experience to determine, but the bone, if by origin a purely membrane one, is certainly here in process 

 of acquiring that direct perichondrial contact with the underlying cartilage that Schleip ('04, p. 351) 

 describes in 29 mm larvae of Salmo. But there is in Scorpaena, even in the adult, no indication of 

 that calcification of the cartilage found in Salmo. It can, however, be positively asserted that the 

 dorsal limb of the vomer, not only of Scorpaena but probably also of all other fishes in which it is 

 developed, has, or may acquire quite difierent relations to the underlying cartilage than that part 

 of the bone that lies upon the ventral surf ace of the cartilage and is developed in the mucous membrane 

 of the mouth. And this apparently difEerent origin and character of these two parts of the bone is 

 of importance in the homologies that I shall now seek to establish. 



Beginning with Scomber, the two stout condylar processes of the head of the vomer of that 

 fish are evidently the homologues of the ascending processes of the vomer of Scorpaena, the external 

 surface of the processes of Scomber being presented laterally forward and but slightly upward (Allis, 

 '03, p. 68), while in Scorpaena it is presented dorsally; and in Scomber, as in Scorpaena, these pro- 

 cesses of the bone seem to be in process of acquiring primary relations with the underlying cartilage. 

 The cartilaginous interspace of the internasal ridge of Scorpaena, partly enclosed as it is between 

 the two ascending processes of the vomer, is thus the homologue of the beak of my descriptions of the 

 chondrocranium of Scomber, and hence of a part of the prenasal process of the chondrocranium ofAmia. 



In Amia, the so-called posterior process of the premaxillary is, as will be later shown, the pro- 

 bable homologue of the articular process, to be later described, of the premaxillary of Scorpaena. 

 It lies directly upon the dorsal surface of the anterior end of the chondrocranium, and also upon 

 the dorsal surface of the preethmoid (septomaxillary) bone (Allis, '98); and the anterior, or proximal 

 end of the maxillary articulates with its ventral surface, and also with the anterior edge of the preeth- 

 moid. The vomer lies immediately ventral to the articular end of the maxillary, and, immediately 

 posterior to that bone, against the ventral surface of the preethmoid. The lateral edge of the preeth- 

 moid encroaches upon the anterior end of the single palatine articular ridge of the ethmoid cartilage, 

 and Supports, rather than forms part of, that ridge. Taking all these facts into consideration, it is 

 evident that the preethmoid of Amia replaces functionally the ascending process of the head of the 

 vomer of Scorpaena, and that if it were to fuse, in Amia, with the underlying vomer, and the vomers 

 of opposite sides were to fuse with each other, a bone functionally the equivalent of the vomer of 

 Scorpaena would arise. But the preethmoid of Amia is a perichondrial bone that has acquired endo- 

 steal relations to the underlying cartilage, while the ascending processes of the vomer of Scorpaena 

 are either purely membrane bones that seem to be in process of acquiring perichondrial relations 

 to the underlying cartilage, or are, perhaps, partly of perichondrial bone that has not yet acquired 

 endosteal relations to the related cartilage. This difference in the character of the bone in the two 

 fishes may however simply indicate that the primary bones develop in a somewhat difierent manner 

 in Amia and teleosts, being perhaps formed, in Amia, by direct ossification of the cartilage, while in 



