630 H. H. SWINNERTON. 



figs. 3, 4). In the adult, when looked at from beneath, this 

 region (ibid., pi. vii, fig. 2) is triangular; and the nasal 

 septum is very massive, extending not merely to the anterior 

 end, but also to the lateral edges of the ethmoid plate or sub- 

 nasal lamina (ibid., pi. vii, figs. 5 — 8). 



In the absence of well-marked laminal or lateral remnants 

 of the ethmoid plate ; in the forward extension of the massive 

 mesethmoid cartilage to the anterior end ; in the removal of 

 the pre-ethmoid cornu (figs. 44, 45, 2^^-') fi'oni tJie end of the 

 rostrum, the typical Acanthopterygian ethmoid departs from 

 that of Alepocephalus, pike, and stickleback, and approaches 

 that of the salmon. There are, however, some Acanthoptery- 

 gians (e. g. Mesoprion) whose ethmoid is but a modification 

 of the other type. 



Only three primary ossifications are present in this region, 

 viz. the two parethmoids and the mesethmoid. 



The mesethmoid is no longer a mere superficial ossification, 

 but it has penetrated in the case of old individuals far into 

 the substance of the cartilage (figs. 20, 42, e. m.). Super- 

 ficially its central area is coated with a thin layer of peculiar 

 cartilaginous tissue (fig. 42), to which I shall return when 

 dealing with the premaxillte. 



In Amia, Bridge (77, p. 615) describes two ossifications in 

 the antero-lateral angles of the subnasal lamina, and regards 

 them as the homologues of the " paired endosteal ossifications 

 which are to be found at the distal end of the great pre-nasal 

 rostrum in the pike." He also suggests that they are homo- 

 logous with the " septo-maxillary bone, described by Mr. 

 Parker as existing in the fioor of the nasal capsules in the 

 frog." Sagcmehl (84, p. 204) agrees with him in homolo- 

 gising this bone with that found in the pike ; but though he 

 regards its homology with the septo-maxillary of the frog as 

 doubtful, he does not venture to give it a new name. In his 

 postliumous work on the Oyprinidee two similarly situated 

 ossifications are described, but here, though they are quite 

 enclosed in cartilage, they are referred to as septo-maxillary 

 bones (91, p. 511). Allis (98, p. 446, et seq.) has recently 



