268 EDWARD PHELPS ALLIS, JR. . 
acquired a cross-commissural connection with each other. A 
basioccipital portion of the dorsal compartment of the tele- 
ostean myodome would then be added to the prootic portion, 
developed as above set forth, whenever an aortal groove similar 
to that in Hyodon had been developed and retained; and a pos- 
terior extension of the ventral compartment would be acquired 
by the recti interni pushing posteriorly between the floor of 
that compartment and the underlying parasphenoid. The 
many variations that I have described above in the myo- 
dome of the non-siluroid Teleostei would then all arise by dif- 
ferent degrees of ossification of the several membranes in this 
region. 
As already stated, the internal carotid arteries of Amia tra- 
verse the presphenoid bolster in order to enter the cavum cere- 
brale cranil, and, although the development of this bolster has 
not yet been worked out, there seems no question that it is 
formed by the hind ends of the trabeculae The median ver- 
tical myodomic membrane of the Teledstei, which in those 
fishes represents the presphenoid bolster of Amia, would then 
also represent the hind ends of the trabeculae. The basisphenoid 
of the Teleostei cannot then be the exact homologue of the pre- 
sphenoid bolster of Amia. The fenestra ventralis myodomus 
of the adult Amia les posterior to the presphenoid bolster; 
it must then be bounded laterally by the so-called anterior 
prolongations of the parachordals, and hence correspond to 
Gaupp’s fenestra basicranialis posterior in embryos of Salmo, the 
fenestra hypophyseos of these embryos apparently being repre- 
sented in the internal carotid canals of Amia. The fenestra 
hypophyseos is said by Gaupp (’05 b, p. 585) to be a persisting 
portion of the large fenestra basicranialis anterior of early em- 
bryos, and it is said by him to be always traversed by the ecto- 
dermal stalk of the hypophysis. The hypophysis must then 
lie, in these early embryos, dorsal to this fenestra, and as the 
internal carotid arteries, in the Holostei and Teleostei, run 
upward anterior to the hypophysis, they must traverse the 
fenestra. The hypophysis must then have later shifted pos- 
teriorly to a position dorsal to the fenestra interparachordalis 
