THE HEAD OF OSTEOLEPIS. 187 



represented by the ' hyomandibular canal ' of Selachians. A further study 

 of this region in the Stegocephali might enable us to determine the homology 

 of the lateral hones of the skull, especially of the quadratojugal, which is 

 still very obscure. Judging from modern forms, the preopercular canal must 

 have been supplied by a postspiracular branch of the hyomandibular nerve; 

 we should not, therefore, expect to find it and the bone containing it in the 

 skull of an Amphibian. Although a canal is known to have been present in 

 the lower jaw of some Stegocephalians, its connexion with the more dorsal 

 canals does not seem to have been made out. The settlement of this 

 important point might help us to determine whether the preopercular is 

 really represented in the Amphibian skull or not. 



In conclusion attention may be drawn to the remarkable uniformity in the 

 structure of the skull among the Osteolepidas. T'hursius, Diploptervs, and 

 even Megaliclithys seem to differ in no important respect from Osteolepis in 

 the number and disposition of the bones on the head. The Iihizodontidse 

 also closely resemble the Osteolepids ; and, except for the presence of infra- 

 dentaries and for the subdivision of the squamosal, the restorations of 

 Rhizotlojisis made by Traquair (12), that most accurate of observers, would 

 serve almost equally well for Osteolepis, as ma)' easily be seen by comparing 

 his figures with mine. 



List of References. 



1. Allis, E. P. : On Certain Homologies of the .... Bones of Amia 



calva. Anat. Anz. vol. xvi., 1899. 



2. Baur, G. : The Stegocephali. Anat. Anz. vol. xi., 1896. 



3. (Jollinge, W. E. : The Sensory Canal System in some Fossil Fishes. 



Proc. Birmingham Phil. Soc. vol. ix., 1895. 



4. Goodrich, E. S. : On the Scales of Fish. Proc. Zool. Soc, 1908. 



5. Vertebrata Craniata, Part 9 of a 'Treatise on Zoology/ 1909. 



6. Gregory, W. K. : The Problem of the Origin of the Tetrapoda. Ann. 



New York Acad. Sci. vol. xxvi., 1915. 



7. Huxley, T. H. : The Systematic Arrangement of the Fishes of the 



Devonian Epoch. Mem. Geol. Survey, 1861. 



8. Jaekel, 0. : Ueber die Epiphyse u. Hypophyse. Sitz. Gesell. Naturf. 



Fr. Berlin, 1903. 



9. Moodie, Pi. S. : Lateral Line of Extinct Amphibia. Journ. Morph. 



vol. xix., 1908. 



10. Pander, C. H. : Die Saurodipterinen des Devon. Systems, 1860. 



11. Poelard, H.B. : On the Anatomy and Phylogical Position of Polypterus. 



Zool. Jahrb., Abt, Anat. vol. v., 1892. 



