The Latero-Sensory Canals and Related Bones in Fishes. 433 



lateral edge and enters the squamosal, where, as already stated, it 

 either ends or anastomoses with the main infraorbital. The nasal 

 bone lodges one sense organ of the line, and the frontal five organs, 

 no organ being found, in the parietal. A primary tube leaves the 

 canal regularly between each two organs, and opens on the outer surface 

 by a single pore. That part of the canal that lies in the parietal and 

 squamosal is the terminal tube only of the line, for it lodges no sense 

 organ. The sixth or penultimate tube of the line is a long one, and is 

 directed almost directly laterally. The corresponding tube in Erythrinus 

 is considered by Sagemehl as the posterior poi'tion of the canal itself, 

 and is said by him to open on to the postero-lateral corner of the 

 frontal. It is, in Macrodon, directed toward and approaches somewhat 

 the 9 th. tube of the main infraorbital canal, and the arrangement 

 would seem to suggest that if these two tubes should meet and fuse, 

 it would produce an anastomosis of the two canals exactly similar to 

 the one that is found in Amia. A little consideration, and more 

 particularly a comparison with Hydrocyon and Alestes, shows that 

 the normal fusion, if it were to take place, would be with the next 

 posterior or 10 th. infraorbital tube, that tube arising from the main 

 canal between the postfrontal and squamosal bones. 



Sagemehl says [64, p. 30] that one of the lateral canals of 

 Macrodon, I can not make out which one, traverses his postfrontal 

 bone. As his postfrontal is the sphenotic (postorbital ossification) of 

 the nomenclature here employed, this is certainly an error. Sagemehl 

 furthei^ says [p. 36]: "Bei den Characiniden ist, wie schon früher 

 hervorgehoben wurde, das Postfrontale von der Schädeloberfläche in 

 die Tiefe gerückt, indem der Dilatator operculi die obere Fläche des 

 Postorbitalfortsatzes zur Insertion benutzt hat. Dadurch hat der ur- 

 sprünglich kontinuierliche Schleimkanal an dieser Stelle eine Unter- 

 brechung erfahren und ist in einen vorderen, supraorbitalen und einen 

 hinteren, temporalen Abschnitt zerlegt worden". This, in so far as it 

 relates to the sensory canals, is certainly an erroneous statement, for 

 the main infraorbital canal is confinons, not only in Macrodon, but 

 also in Hydrocyon and Alestes. 



The supratemporal canal of Macrodon lies mainly in the so-called 



Internationale Monatsschrift für Anat. u. Phys. XXI. 28 



