On certain features of the lateral canals and cranial bones of Polyotlon folium. 667 



branch of the glossopharyngeus going to any of the organs of the 

 lateral line system, and that a branch of the vagus, which innervates 

 the anterior portion of the lateral canal of the body, "also innervates 

 the cluster pores in the occipital region". This probable innervation 

 of the commissure, together with its origin from the main canal 

 slightly anterior to the suprascapular, clearly indicates that it must 

 be the homologue of the supratemporal commissure of Amia and 

 tcleosts, and that the two enclosing ossicles must accordingly represent 

 all, or a part, of the extrascapular (supratemporal) bone of the fish. 

 The lateral one of the two ossicles, on this side of this fish, did not 

 enclose any portion of the main canal. In all the other dissections 

 made, and as shown on the left side in the figure, it enclosed a part 

 of that canal both anterior and posterior to the Commissure, the 

 lateral ossicle of the commissure apparently fusing with that ossicle 

 of the main line that lies between it and bone C\ and the united 

 ossicles then not only encroaching upon the canal anterior to the 

 commissure, but often also fusing with the mesial ossicle of the com- 

 missure. A single T-shaped bone thus often arises which encloses 

 the commissure and a short section of the main canal, exactly as the 

 extrascapular does in Amia. The primary tube that arose, on the 

 right side of the figure, at the middle of ossicle 1, arose, in most of 

 the other dissections, directly opposite the lateral end of the com- 

 missure; and was enclosed, nearly to the point where it begins to 

 branch, in a delicate tube of bone. This enclosing of the primary tubes 

 in bone, it may here be mentioned, is the general rule in Folyodon. 

 Anterior to this T-shaped extrascapular bone, between it and 

 bone C^ there were, in the several specimens, either two, three, or 

 four lateral sensory ossicles, with three or four related primary lubes. 

 There is thus, in these little bones, an evident tendency to fuse, and 

 they would seem to represent a single cranial element; for in no 

 case were any of them fused either with the extrascapular or 

 with the bone CI Their position would seem to indicate that 

 they represent the entire lateral canal component of a squamosal 

 bone, and as such I should certainly consider them if Bridge and 

 CoLLiNGE had not both considered bone C^ as the dermo-sphenotic. 

 This will be further discussed below; but as these ossicles cer- 

 tainly form part, if not the whole, of the lateral component of the 

 squamosal, they will be for convenience referred to as the squamosal 

 ossicles. 



Znol. Jahrb. XVII. Abth. f. Morph. 43 



