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THE OSTEOLOGY OF AMIURUS CATUS 

 (L.) GILL. 



BY J. PLAYFAIR McMURRICH, M.A. 

 Professor of Biology in the Ontario Agricultural College. 



[Read before the Canadian Institute, February the 16th, 188!,.] 



Numerous statements regarding the osteology of the Siluroids 

 have appeared from time to time in various works, such as the text- 

 books of Stannius, Huxley. Glaus, Wiedersheim, etc., and in many 

 scattered papers, but, as far as I can discover, no complete study has 

 been made of any one form. In the following pages I desire to re- 

 count the results of a detailed study of the various osteological 

 elements of our common Canadian Siluroid, Amiurus catus (L.) 

 Gill. The description of the various portions of the skeleton will be 

 accompanied by some notes on the development of certain bones, as 

 far as it has been possible to trace them, and a few remarks of a 

 comparative nature. 



I.— THE CRANIUM. 



Viewed as a whole the cranium is extensively flattened, tapering 

 from behind forwards in depth, so that a vertical longitudinal section 

 would present a triangular aspect. Posteriorly are seen the five 

 processes characteristic of the Teleostean skull, those of the pterotics, 

 epiotics, and the median elongated supraoccipital spine. No well 

 defined orbit is present, the postorbital process of the sphenotic being 

 exceedingly small. A well marked antorbital process is, however, 

 present, and in front of this at the anterior extremity of the skull 

 two more lateral processes are formed by ossification of the lateral 

 expansions of the ethmoid cartilage. On the upper surface of the 

 skull are two median fontanelles ; the anterior is the broadest, and 

 is bounded by the frontals behind, and slightly by the mesethmoid 

 in front ; the posterior, which is long, tapering posteriorly, is bounded 

 in front by the frontals, and posteriorly separates the supraoccipital 

 into two halves, nearly as far back as the posterior surface of the 

 skull. In accordance with the flattening of the skull, the canal for 



