682 ALLIS. [Vov. XII. 
tores of all fishes, and not as a specially developed condition of 
the interbranchiales of other fishes. From the dorsal end of 
this primitive muscle the interarcuales of selachians and the 
levatores arcuum branchialium of ganoids and teleosts arise ; 
from its ventral end the obliqui ventrales of the latter fishes. 
The adductores can now be considered. In Amia and 
teleosts they seem to represent, on the branchial arches, the 
greatly reduced and disappearing middle portion of the once 
continuous interbranchiale of Chimaera. They cannot, how- 
ever, always be derived from that muscle, for in Chimaera both 
an adductor and an interbranchiale are found on each of the 
first three arches. Whether they arise from that muscle, or 
with it from the same deeper layer of the general constrictor, 
they, in Amia, reach their position on the inner surface of the 
arches by passing backward and inward over the hind edge of 
the arch. This the innervation shows conclusively. 
In the hyoid arch the hyohyoideus superior is unquestion- 
ably the true interbranchial muscle of its arch; that is, a 
muscle homologous with the interbranchiales of selachians and 
not with those of Chimaera. From the dorsal portion of this 
muscle the levator and adductor operculi of Amia arise. These 
latter muscles are accordingly not the serial homologues either 
of the external or the internal levator muscles of the branchial 
arches. The homologue of one or both of those muscles is 
certainly the so-called adductor of the arch, the adductor hyo- 
mandibularis. The origin, insertion, and innervation of the 
muscle all indicate this almost conclusively. The other inter- 
arcual muscle or muscles of the arch are found, in Amia, in 
one or both of the two ligaments on the inner surface of the 
hyomandibular. The ligaments, in Amia, have entirely lost 
their attachment to the first branchial arch. In certain selachi- 
ans they still retain it (No. 38). Other ligaments, in selachians, 
connect the hyomandibular with the skull and represent the 
levator, or so-called adductor, hyomandibularis, which muscle is 
otherwise entirely wanting. The hyohyoideus inferior may be 
the obliquus ventralis of the arch. 
In the mandibular arch the levator arcus palatini develops 
from the superficial portion of the general constrictor, and is, 
