482 Edward Phelps AUis jr., 



to the postfrontal bone are all innervated by branches of the ramus 

 buccalis, the innervation showing that there are probably as many 

 organs as primary tubes. In the postfrontal bone there is a group ot 

 organs lying close together opposite the one primary tube that leaves 

 the canal as it traverses the bone. They are all innervated by short 

 branches of a single long nerve that has its origin from the ramus 

 oticus, the short terminal branches of the nerve showing that the sen- 

 sory structures it innervates are quite certainly simply parts of a pri- 

 marily single sense organ. The remaining and larger portion of the 

 ramus oticus goes to the squamosal and there innervated, in the smaller 

 one of my two specimens, four organs on one side of the head and 

 three on the other. These organs, as seen in figure 38, are grouped 

 near the central portion of the squamosal, practically opposite the point 

 of anastomosis of the main infraorbital canal with the supraorbital, one 

 organ, on each side of the head, lying immediately anterior to the point 

 of anastomosis, and the others opposite or posterior to that point, and 

 quite regularly between each two adjoining tubules. Compared with 

 selachians and teleosts, it would look as if the otic group of several 

 organs in the former, was here, in Acipenser, in process of being con- 

 densed into the single otico- squamosal organ of certain teleosts. A 

 branch of some postfacial nerve, it could not be determined which, ana- 

 stomoses with the terminal portion of the ramus oticus, and may contain 

 latero-sensory fibres destined to innervate certain of the organs in the 

 squamosal. Branches from it, and also from the oticus, go to the large 

 squamosal patch of nerve sacs. In the lateral extrascapular there was 

 one sense organ in the main canal, slightly anterior to the supra- 

 temporal canal, and it was innervated by a branch of a postfacial 

 nerve, that nerve innervating also those organs of the supratemporal 

 canal that lie in the lateral extrascapular, and also the extrascapular 

 group of nerve sacs, and apparently also the organ or organs of the 

 middle head canal, to be described below. The innervation of the 

 main infraorbital posterior to this point was not traced. 



The supratemporal canal, as already stated, leaves the main infra- 

 orbital as that canal traverses the lateral extrascapular. Running 



