374. HOWARD AYERS 
The muscles of Bdellostoma have been differentiated to such 
a degree beyond the Ammocoete condition that they have not 
yet been reduced to a grouping that permits comparison with 
Ammocoetes. IJ had planned to publish an account of the muscles 
of Bdellostoma in 1898; it would not have cleared many of the 
problems seeking solution. That paper went to the waste- 
basket two years later. Since then I have sought a basis for 
comparison of the muscles of Bdellostoma with both lower and 
higher forms. In 1896, F. J. Cole published a very full account 
T Ae SSE Nn ee eee 
f a og 
Fig. 25 Dissection of the left side of skeleton of jaw apparatus of Bdellostoma, 
to show the relation of its parts with dentigerous jaw protruded and retracted. 
The hyoidean mechanism bears the tentacular portion of the jaw bars fastened 
to its anterior end, thus leaving the dentigerous jaws free to move unhampered. 
of the muscles of Myxine with frequent references to the muscles 
of Bdellostoma, but he recognized that the comparative mor- 
phology of his subject was not ripe for solution. What is here 
offered is a grouping of the Myxinoid muscles based on the 
comparative anatomy of the jaw apparatus as outlined within. 
It is evident that we have to deal with two quite distinct 
major groups of muscles associated with the jaw apparatus. 
The first and oldest group is that of the intrinsic muscles of 
the jaw apparatus which are developed out of the ventral plate 
of transverse muscle fibers of the Amphioxine ancestor. Al- 
ready in Amphioxus the group of intrinsic muscles is sharply 
