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The supratemporal bones of Polypterus are thus not, according 
to Mager, the homologues of the epiotics and supraoccipitals of the 
Stegocephali, and the related sensory canals can not, accordingly, be 
homologous. As the canal in Polypterus lies, according to Maget’s 
determinations, morphologically anterior to the one in the Stegocephali, 
it would seem necessarily to become the homologue of the middle 
head line of pit organs in Amia, and not of the supratemporal cross- 
commissure of that fish. While this may be found to be the case, 
it certainly seems most improbable. 
In very young sturgeons the interpanjetals of 1 man and of Poly- 
pterus are said by Maaer to be found as “quatre plaques osseuses 
rétropariétales également en série transversale, dont, chez les adultes, 
les médianes se fondent entre elles, tandis que les latérales restent 
distinctes”. The median plates are then said also to fuse with a 
median rhomboidal plate that lies anterior to them, and that is said 
to be formed by the fusion of two triangular plates found one on 
each side of the head of young larvae. Each of these two latter tri- 
angular plates is said to represent two of the four preinterparietal 
centers of ossification of man, and, hence, also a lateral half of the 
single, median, rhomboidal, preinterparietal plate of Polypterus. The 
fusion of these four distinct bones, or six centers of ossification, of 
the young sturgeon are said to give origin to the bone called by 
Hux ey in the adult fish, the supraoccipital. The lateral retroparietal 
plate, on each side of the head of the young sturgeon, becomes, so 
far as I can understand Maaat, the epiotic of HuxLey’s descriptions 
of the adult, and it and bone I of HuxLey are together the homologues 
of the lateral interparietals of man. 
In the Stegocephali the interparietals of Maaai’s discussion are, 
as already stated, the four bones usually called the supraoccipitals 
and epiotics, and these bones are, accordingly, the homologues, not of 
the median four supratemporal bones of Polypterus, but of the four 
osseous plates that, lie transversely, posterior to those bones. The 
preinterparietals are said to be rarely found distinct in the Stego- 
cephali, the two anterior ones being almost always fused, each with 
that so-called parietal of the animal that lies immediately in front of 
it, and the two posterior ones fused with the interparietals. The so- 
called parietal of the animal is not, according to Maaat, the homologue 
of the parietal of Polypterus, but is the homologue of that bone of 
Polypterus fused with the mesial retroparietal or postparietal (supra- 
temporal) of the fish. The parietal of the Stegocephali is thus the 
