No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 591 
In Galeus Csd2 arises, as it does in Scymnus and Acanthias, 
from the upper, outer corner of the skull, from the line mark- 
ing the position of the lateral canal of the head, and from the 
tendinous streak which extends upward and forward from the 
upper end of the first gill slit. That part of the muscle that 
arises from the skull has, however, been differentiated as a 
wholly separate muscle and lies immediately external to the 
anterior part of the rest of the muscle, the front edges of the 
two exactly coinciding. It is a thin, delicate, band-like muscle, 
nearly as broad as it is long, inserted entirely on the hyoman- 
dibular and lying immediately external to the large spiracle 
muscle. The facialis, as it runs outward around the front edge 
of the muscle below the spiracle muscle, sends a branch out- 
ward and then backward along its outer surface to supply it. 
It thus corresponds in its innervation to the adductor hyoman- 
dibularis in Amia, and but slight changes in origin and inser- 
tion would be needed to produce that muscle. The muscle 
in Galeus has simply to travel backward at its origin beyond 
the origin of the spiracle muscle and then downward along the 
side of the skull. If this little muscle in Galeus is the homo- 
logue of the adductor hyomandibularis in Amia, the remaining 
larger portion of Csd@2 must either disappear or, more probably, 
give rise to the opercularis in Acipenser, and to the adductor 
operculi and levator operculi in Amia, which muscles arise 
wholly or in part from the dermal bones of the head, as does 
the muscle Csd@2 in Galeus. 
In Chimaera the adductor operculi and the levator operculi 
are probably represented by Csz ; the retractor hyomandibularis 
of Acipenser and the adductor hyomandibularis of Amia being 
represented by the muscle which Vetter has called the hyoideus 
superior, and which he considers the homologue of the superior 
division of the hyohyoideus in teleosts. 
5. Nervus Trigeminus and Nervus Facialis. 
The several branches of the nervus trigeminus and nervus 
facialis arise from what is commonly called in fishes the Gas- 
serian ganglion, or, more properly, the trigemino-facial gangli- 
onic complex. This ganglion, in the adult Amia, lies in the 
