422 Julia B. Platt 
skeleton lends support to the view that the trabeculae were prim- 
arily bars of a prae-oral visceral arch. 
SEWERTZOFF (97, page 422) notes that in embryos of Acipenser, 
Petromyzon, and of the Amphibia, where the mesocephalic flexure 
_ of the brain is slight, the trabeculae lie in a position nearly horizontal, 
while in those animals which have a prouounced mesocephalic flexure, 
as in the Selachian embryo, the trabeculae are almost vertical. 
From this correlation between cranial flexure and direction of the 
trabeculae, SEWERTZOFF concludes that the primary function of the 
trabeculae was that of supporting the brain. 
I regret that SEWERTZOFF does not tell us the position of the 
mouth cleft in these embryos, for should it appear that the trabe- 
eulae are horizontal in position when the mouth cleft, dorsal (rela- 
tively anterior) to which they lie, is horizontal, and vertical when 
this cleft is vertical, a correlation might be found leading to quite 
different conclusions. | 
SEWERTZOFF, moreover, includes the Amphibia among those 
forms in which, with slight mesocephalie flexure of the brain, the 
trabeeulae lie almost horizontal. I believe no power of imagination 
could lead one to describe the procartilage, camera outlined in 
fig. 8, as a nearly horizontal bar. When this bar of procartilage is 
converted into cartilage, it does, indeed, lie horizontally, but so also 
do the mandibular bars which bound the mouth cleft ventrally (rela- 
tively posteriorly), yet their horizontal position proves nothing against 
the primitive branchial function of the bars. 
Part IL. 
The Cartilaginous Skull. 
The anatomy of the skull in Menobranchus (Necturus) has 
been described by Huxrey (74), and the development of the Urodel 
skull, as observed in Triton and Siredon, has been carefully 
studied by Srénr (’80). In the following account, I shall conse- 
quently note chiefly such points as seem to me of some importance, 
wherein the development of the skull in Necturus differs from that 
of Triton and Siredon, as described by SrtöHr, attempting to 
make this part of the study merely supplementary to the admirable 
papers of Huxrey and STÖHR, rather than complete in itself. 
