On the Anatomy and Phylogenetic Position of Polypterus. 



409 



the quadrate or possibly to degenerate into a cartilaginous tympanic annu- 

 lus then the operculum must, if it is to remain, fix itself to the quadrate. 

 In Stegocephali there was apparently no hyomandibular and the oper- 

 culum did shift forwards somewhat and attach itself to the quadrate 

 becoming the supratemporal, so called, the squamosum of Amphibia 

 and Reptilia (Baur). The other elements of the opercular series also 

 shifted forwards and became somewhat reduced, the suboperculum be- 

 coming the quadrato jugal and the praeoperculum the jugal. The small 

 plates below the praeoperculum appear to be lost. 



The accompanying woodcuts represent Polypterus and a Stego- 

 cephalan. The general similarity will be seen. 



Woodcut 1. Woodcut 2. 



Woodcut 1'). Surface of skuH of Polijpterus , chiefly from Wiedersheim, with 

 the mucous canals marked in deep lines. 



Woodcut 2. Metopias diagnosticus from Zittel. 



Dermethmoid (abs. in Metopias), 1 Nasal, 2 Frontal, 3 Parietal, 4 Squamosal 

 (piscine), 5 Premaxilla, 6 Anterior suborbital or lachrymal, 7 Maxilla, 8 Postfrontal, 

 9 Posterior suborbital or postorbital, 10 Preoperculum or jugal (reptilian), 11 Oper- 

 culum or squamosal (reptilian) or suprateniporal (stegoceplialan), 12 Suboperculum or 

 quadratojugal , 13 Supratemporals or dermosupraoccipitals, 14 Posttemporal scale or 

 epiotic (Gehördeckknochen), Jugal (piscine) abs. in Metopias. 



1) In Woodcut 1 the opercular mucous canal is wrongly joined to 

 the main cranial. Careful study of Polypterus and comparison of figures 

 of fossils (Pander) show that a canal formerly ran back in the pre- 

 operculum. I have had occasion to revert to the subject in a later 

 paper. 



