The Latero-Sensory Canals and Related Bones in Fishes. 411 



re-anastomosed with each other in such a way as to give rise to a 

 most complicated system of canals and branches. Collinge has called 

 attention to this, and his figures are said by him to "diagrammatically 

 represent, so far as is possible in a drawing, this network of branches". 

 But certain of the canals shown in those drawings do not belong to 

 the latero-sensory system, and, what is equally unfortunate, other canals 

 or tubes that do belong to it are not even indicated. In my figs. 2, 

 3 and 4 these dendritic systems are all shown on one side of the head, 

 and the cut trunks, or demi-trunks, on the other. These figures are 

 necessarily large, and perhaps occupy more space than the subject 

 warrants. But they present a typically exaggerated condition of the 

 dichotomizations and subsequent interanastomoses of the primarily simple 

 primary tubes of the latero-sensory system, found in no other fish 

 known; and, aside from showing the possibilities in this particular 

 line of development of the system, they may serve to explain certain 

 conditions found in fossil fishes. The resulting canals and tubules 

 are so complicated that I shall not attempt to in any way describe 

 them, the figures themselves amply sufficing. It may however be 

 stated that the interanastomoses of the dentritic s, stems give rise, in 

 many places, to what might be considered as a system of two or 

 more parallel and intercommunicating canals. 



The ethmoidal section of the main infraorbital canal begins in 

 the median line of the ventral surface of the extreme anterior end of 

 the snout, there being continuous with its fellow of the opposite side. 

 The canal there lies in a median dermal bone, the prenasal of 

 Parker's [58] and Collinge's descriptions, but this bone is certainly 

 the strict homologue of the dermal ethmoid bone of Amia. In this 

 bone a median primary tube arises from the canal, and the canal from 

 there runs laterally and then downward and backward in the bone, 

 to its hind edge, where it enters a bone that is clearly the homologue 

 of the antorbital bone of Amia. This antorbital bone is called by 

 Collinge the premaxillary, but nothing is said as to its bearing teeth. 

 By Parker I can not find that it is particularly described, but it 

 would certainly seem to form no part of the premaxillary of his 

 descriptions. In it, latero-postero-ventral to the posterior nasal aperture, 



