On the Anatomy and Phylogenetic Position of Polypterus. 421 



the higher level of the sacculus, the elongation of the external semi- 

 circular canal and in the division of the auditory nerve Polypterus 

 shows distinct Urodelan characters. I failed to find the ductus and 

 Saccus endolymphaticus but as depicted by Retzius the saccus shows 

 a difference from the other Ganoids in its expansion and leads to the 

 condition of higher vertebrates. 



As is well known the ribs in Polypterus represent an ontogenetic 

 stage in the Urodela. In the Stegocephali the ribs are formed of 

 two different elements fused together. 



ZiTTEL (Handbuch der Paläontologie) denies that the Amphibia 

 can be derived from the Stegocephali direct but then comparatively 

 little is known of their primordial cranium and of their anatomy 

 generally where as Polypterus which I take to represent fairly well 

 the ancestor of the Stegocephali shows especially in these regions and 

 not in the dermal bones the characters, which must be assigned to 

 the ancestral form of the Amphibia. Polypterus is fitted to be the 

 ancestor of Amphibia in so far as its teeth are simple but allied 

 Crossopterygidae possessed Labyrinthodont teeth. 



Conclusion. 



In the present paper it has been my endeavour to trace the 

 relationships of Polypterus below to the most archaic Selachii, above 

 to the Stegocephali and Amphibia. To this end I have described and 

 compared the muscles of the cranial region and have done my best 

 to fill up gaps in our knowledge of the peripheral nervous system, 

 the cranium, dermal bones, palatal region, shouldergirdle and pec- 

 toral fin, bloodvessels and jaws. Incidentally points which I believe 

 to be new have been noted in the fate of the retractor hyomandi- 

 bularis muscle, in the relations and history of branches of the Trige- 

 minal and Facial nerves as well as perhaps of the Vagus, in the 

 wandering of the pineal aperture, in the origin of the columella, in 

 bone formation, in the homologies of the opercular series and in the 

 origin of the humerus. 



Should only part of the results stand the test of further re- 

 search it will be seen how true is the sentence of Agassiz: 



"L'étude de la tête de ce poisson ouvre, comme on vient de le 

 voir, un champ entièrement neuf à T Ichthyologie". 



July 1891. 



