ON THE UROSTYLE OP THE ANUROUS AMPHIBIA. 239 



19. A. Note on the Urostyle (Os Coccygeum) of the Anurous 

 Amphibia. By Geo. E. Nicholls, D.Sc., F.L.S., late 

 Professor of Biology, Agra College, Agra, India *. 



[Received January 20, 1915 : Read April 13, 1915.] 

 (Text-figure 1.) 



Morphology. 



It is, I believe, generally supposed that the neural canal in 

 the Anura ends blindly in the urostyle. That this is nob true of 

 Rana ternporaria — at any rate, in the young animal — I ascertained 

 so far back as 1910, when examining sections (cut sagittally) 

 through small frogs. In these sections the filum terminal e is seen 

 lying uncovered (except for connective tissue) upon the dorsal 

 surface of the urostyle. 



At that time, however, I paid no further attention to the 

 matter, assuming that this was merely a transient condition- in 

 the young animal in which the absorption of the terminal 

 portion of the filum terminale was not yet completed. I imagined 

 that the resorption of tissues, which causes the disappearance 

 of the tadpole-tail, would continue, and that, finally, what re- 

 mained of the terminal filament would become entirely encased 

 in bone. Unaccountably, it did not then occur to me to examine 

 the adult urostyle. 



While in India, however, I had occasion to examine closely 

 the urostyle of Rana tigrina, the type commonly dissected in my 

 laboratory there. 



The urostyle of this species differs from that of Rana tempo- 

 raria in the exceedingly variable occurrence of the paired per- 

 forations, which, in the latter species, admit of the exit of the 

 tenth pair of spinal nerves. These perforations are, in Rana 

 tigrina, frequently absent (text-fig. 1, a, c, d). When present 

 (text-fig. 1, b, X.) they are extremely minute, and commonly, upon 

 one side or the other, the external opening leads only .into a 

 blindly-ending canal. 



It was while engaged in studying the urostyle in connection 

 with this matter that I noticed that the neural canal turned 

 upwards very sharply, and apparently extended quite to the 

 dorsal margin of tbe bone. The position and extent of this 

 passage is clearly indicated (in the fresh condition), through the 

 thin translucent bone, by the deeply pigmented meningeal 

 sheath of the filum terminale and its related blood-vessels. 



A recollection of the perforated condition of the urostyle 

 which I had observed in the young R. temporaries led me to 

 examine the upper margin of the urostyle with the aid of a 

 powerful lens. 



* Communicated by Prof. Arthur Dendt, D.Sc, F.R.S., F.Z.S. 



17* 



