No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 643 
(No. 121, p. 186), in every detail with the fasciculus communis 
of fishes and Amphibia. 
III. MUSCLES INNERVATED BY THE GLOSSOPHARYNGEUS 
AND VAGUS, AND THE NERVI GLOSSO- 
PHARYNGEUS AND VAGUS. 
1. The Visceral Arches. 
The visceral arches in Amia have been described by Bridge 
(No. 15) and by van Wijhe (No. 129). There are seven of 
them in all, the mandibular, or perhaps more properly palato- 
mandibular, arch, the hyoid arch, and five branchial arches. 
Of the latter, four are complete arches bearing each a double 
row of gill filaments, while the fifth is a half arch without gill 
filaments. 
Between the fifth arch and the next preceding, or fourth arch, 
the gill opening lies entirely on the ventral aspect of the arches, 
and does not extend to their hinder, outer angle ; that is, it lies 
between the ceratobranchials only, of the two arches, and does 
not extend upward onto the dorsal aspect of the arches 
between the epibranchials, as is the case with the other open- 
ings. Between the fifth arch and the next following, or pec- 
toral arch, there is a relatively large space, closed externally by 
a thin layer of integument which extends upward and forward, 
beyond the upper end of the fifth arch, along the posterior edge 
of the dorsal portion of the fourth arch, and then forward, 
across the dorsal ends of that arch and the other anterior 
arches, median or proximal to the gill filaments, to the inner 
upper angle of the operculum. 
Immediately internal to the dorsal portion of this thin mem- 
brane, and attached to it, there is, in the adult, a much degen- 
erated glandular formation, extending from near the upper 
anterior corner of the opercular opening back to the front 
edge of the supraclavicular. It is evidently the thymus, but 
apparently so degenerated that it disintegrates and floats away 
when stirred with a scalpel under water, or even when washed 
with a pipette. In embryos it is found as a well-defined, rela- 
tively large mass, not at all degenerated in appearance, and not 
