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not, however, fused into a common cell mass as CornınG (’95) states 
for Seyllium, but show their primary metamerism, which is still further 
evinced by the five ventral nerve roots related to them. The anterior 
myotomic bud, which is quite as long as the following four taken 
together, has become differentiated into two distal portions, a median 
and lateral, comparable with the bipartite buds which enter the 
appendages. This anterior segment of the hypoglossus musculature 
(derived from the 4th postotic myotome) corresponds with the “peri- 
phere Abschnitt” of the ,,Zungenstrang” which MoLLIEr (95) has 
described in Lacerta. It later comes to lie between the hyoid and 
mandibular cartilages and thus forms in part the Anlage of the proper 
tongue muscles. The four following myotomie buds come to lie 
between hyoid and procoracoid. 
Five ventral spinal nerve roots innervate the hypoglossus muscu- 
lature at this stage. These are the nerve roots of the 4th to 8th 
post-otic myotomes, i. e. of VAN WisHE’s 8th to 12th somites. The 
ventral root of the 3rd post-otic myotome is present!), but it is somewhat 
rudimentary and has no connection with sub-branchial musculature. 
Branches from the 7th and 8th post-otic myotomes enter the pectoral 
plate as finally do those of at least eleven of the following myotomes. 
Thus having found evidence that the same number of myotomic 
buds form the Anlage of the ventral longitudinal muscle in the 
branchial region both of Petromyzon and Squalus (compare CoRNING’s 
[’95] results), are we to conclude that these five?) myotomes are 
exact homologues? Surely not from the evidence of their numerical 
correspondence alone. Such an homology would be especially doubtful 
since these myotomes lie in that region of the embryo, where there 
has occurred phylogenetically a reduction at least of ventral segments, 
and where marked “metamerische Umbildungen” take place during 
ontogeny. In order to determine an exact homology of a metamere 
or a portion of a metamere in Squalus and Petromyzon, it is quite 
1) Horrmann (’94) incorrectly states that this nerve root disappears 
in very early stages. I find it present even in embryos of 4!/, to 5 cm. 
2) I do not wish to seem to lay too much stress upon the fact 
that the anterior eight segments of the ventral longitudinal muscle of 
Petromyzon, to which 1 have for convenience given the name M. par. 
subbranchialis, are derived from the buds of the first five post- 
branchial myotomes. It would he difficult indeed to maintain that there 
is any fundamental distinction between the buds of these five myotomes 
and those of the following myotomes, since the musculature formed by 
them is perfectly continuous, 
