[270] 
THE OSTEOLOGY OF 4MIURUS CATUS 
(L) GILL. 
BY J. PLAYFAIR McMURRICH, M.A. 
Prosessor of Biology in the Ontario Agricultural College. 
{Read before the Canadian Institute, February the 16th, 1884.) 
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, Claus, 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, Anwiwrus 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 pteroties, 
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 
