No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 667 
being the homologue of the protractor hyomandibularis of 
sturgeons. The spiracle is also probably not inconstant in its 
relations to the hyomandibular if one does not first accept the 
conclusion that “the hyomandibular of Teleostei must be sought 
in the articular portion of the quadrate of Heptanchus.” 
Regarding Pollard’s cirrhostomial theory, in general, I find 
nothing in Amia, so far as my work has gone, that seems in any 
way to support it. On the contrary, everything seems to indicate 
the development of the mouth parts from visceral arches. As 
to the tentacles of fishes, at least of all gnathostome fishes, I am 
strongly inclined to think that they are simply special sensory 
structures developed in connection with terminal buds, or per- 
haps of such buds and also of other organs more nearly related 
to the pit organs of Amia. That procartilaginous or even car- 
tilaginous or bony pieces, such as Pollard describes, should 
develop in connection with such accumulations of these organs 
is not surprising, if dermal sense organs are, as Klatsch states 
(No. 65), active centers of ‘“skleroblastic ’ formation. 
It is perhaps worthy of note that in Amia there is a little 
fold or flap of dermal tissue on the upper edge of the lower 
jaw, just in front of the coronoid process, that is, about where 
the coronoid tentacle of siluroids is found. A similar fold is 
found in Esox and Scomber also, and doubtless in other teleosts 
as well. If these folds be sensory structures, as they seem to 
be, they may be the homologues of, or at least represent a 
certain stage in the development or degeneration of, the ten- 
tacles. 
2. Levatores Arcuum Branchialium. 
The levatores arc. branch. (Figs. 52-59, Pls. XXXIV and 
XXXV) area group of straight, diverging muscles, arising close 
together from the well-marked ridge that extends medianward 
and forward along the side of the skull from the hind end of the 
posterior process of the intercalar. The surface of origin lies 
immediately median to and below that of the posterior portion 
of the adductor hyomandibularis, and immediately lateral to and 
above that of the anterior end of the trunk muscles, which, in 
the adult, extend forward beyond the hind margin of the leva- 
