22 H. B. POLLARD. 



In Silurus the premaxillary piece is represented by precartilage 

 above and between the premaxillary bones. In many Teleostei it becomes 

 a solid block of cartilage. It is mentioned by Stannius as a special 

 part of the snout in front of the nasal septum. " In Gottus and Belone, 

 a small discrete cartilage, applied to the anterior end of the skull, is 

 covered by the premaxillae." " In M althaea it forms a considerable 

 free projection on the skull" (Stannius). 



Sagemehl gave the rather unsatisfactory name " Rostrale " to this 

 block and mentioned its existence in Scomberesocidae, Cyprinodojilidae, 

 Scopelidae, Cyprinidae, Anacanthini (Macrurus), Acanthopteridae and 

 Plectognathi. " From its relations to the premaxillae we have every 

 ground for the supposition that it originally formed the basis (Grund- 

 lage) of these bones. The fact that it occurs in far removed forms of 

 Teleostei allows the conclusion that it is of great antiquity, and thus 

 we may expect to find it in lower fish." " It is found in most distantly 

 related groups, and this points to its being an inheritance from a very 

 remote ancestral form." 



Sagemehl goes on to compare it to a small cartilage between the 

 ends of the palato-quadrate in Heptanchns. This view cannot be correct. 

 Since it is unpaired the piece cannot, according to Sagemehl, corres- 

 pond to a labial of Selachii. A premaxillary block also occurs in the 

 Pharyngognathi (Labrus) and probably in mauy others not yet investi- 

 gated, especially where the premaxillae possess a vertical upward 

 projection, sliding on the ethmoid region. Among the older anatomists 

 this piece has apparently also received the name prenasal cartilage, but 

 I have not succeeded in running this term down. 



An interesting feature in connection with this block is that the 

 median velar support is shown by comparison to be a posterior prolonga- 

 tion from it serving to support the velum or fold of respiratory 

 function, which lies behind the premaxillae. " In many Teleostei, 

 mucous folds, placed behind the jaws, hinder the outflow from the 

 mouth of the water which has been gulped in " (Stannius). The 

 median velar tentacle-like structure is shown in Silurus and Tricho- 

 mycterus (Figs. 3 and 5) and it occurs in many Teleostei. There may 

 be also a lower median tentacle-like support of a lower velum, and 

 these two give the appearance shown in Silurus (Fig. 3), It is the 

 mode of development of these structures in the embryo which has 

 given rise to the views of some embryologists on the paired nature 



