441 
terus are generally considered, as the name implies, as the homologues 
of the one or more supratemporal bones of Teleosts, and also of the 
single supratemporal, or extrascapular, bone of Amia, the name extra- 
scapular having been given by SAGEMEHL to the bone in this latter 
fish. If the three bones of Polypterus be the homologues of the single 
bone of Amia, the main infraorbital canal should not, in Polypterus, 
normally and primarily traverse the second ossicle of the series. It did, 
however, traverse a portion of that bone in the 44-cm specimen. 
Thinking this must be a secondary arrangement I examined a 30 cm 
specimen. In this specimen the canal is not entirely enclosed in the 
second ossicle of the series, as shown in ‘the accompanying figure 3. 
The canal is thus secondarily enclosed in this ossicle, the ossicle being 
primarily formed in relation to the commissure and not in relation to 
the main infraorbital canal. If the commissure in Polypterus should 
be turned backward, at its lateral end, so as to open into. the main 
infraorbital canal opposite organ 12 of that line, or if this organ No. 12 
and the ossicle that encloses it should be pushed forward somewhat, 
exactly the arrangement found in Amia would arise. 
The supratemporal cross-commissure of Polypterus thus agrees in 
every important respect with that of Amia, it being assumed that it 
is innervated by a branch of the first, or supratemporal branch of the 
nervus lineae lateralis, as seems evident from POLLARD’s descriptions. 
Further confirmation of this conclusion is found in the fact that a line 
of surface sensory organs is found in Polypterus occupying a position 
corresponding closely to that of the middle head line of pit organs 
of my descriptions of Amia. This must certainly have an important 
bearing on the homologies that Mager attempts to establish for the 
bones the commissure traverses, and that were referred to at some 
length in one of my a earlier works (No. 5). 
The Supraorbital Canal begins at a single pore that lies 
immediately posterior to the nasal tube. From there the canal curves 
mesially and forward around the base of the nasal tube, traversing 
the os terminale of TRAQuAtR’s descriptions. The first sense organ of 
the line lies in this bone. At the anterior end of the bone the canal 
turns sharply backward and enters the anterior end of TRAQUAIR’S 
accessory nasal bone. At this bend, where, normally, tube No. 2 of 
the line should be found, the canal anastomoses with the main infra- 
orbital canal, joining that canal opposite to, or slightly mesial to, the 
second sense organ of the line. There is here a somewhat enlarged 
space in the main infraorbital canal, from which the double system 2 
infraorbital-2 supraorbital takes its origin. The supraorbital canal, 
