No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 751 
middle portion, where it passes into the mandible, and is 
almost completely separated into two portions, a deeper and a 
superficial one. The latter, in its superior portion, is again 
incompletely separated into two or three portions. The most 
superficial of these portions is probably the homologue of the 
entirely independent superficial muscle of some teleosts. 
34. The adductor hyomandibularis, adductor operculi, and 
levator operculi are derived from the dorsal half of the general 
constrictor of the hyeid arch, the adductor hyomandibularis from 
the deeper layers of that muscle, the other two, or at least the 
levator operculi, from its superficial portions. The adductor 
hyomandibularis is probably developed from a muscle com- 
parable to one or more of the interarcual muscles of the 
branchial arches of selachians, and is thus homodynamous 
with the levators of the branchial arches of teleostomes, and 
not with the adductor mandibulae. The adductor operculi and 
levator operculi, at least the latter, are derived from the inter- 
branchial muscles of their arch, and are thus homodynamous 
with the levator arcus palatini, and not with the levator mus- 
cles of the branchial arches. 
35. The adductors of the branchial arches arise from, or in 
connection with, the arcuals of their respective arches, muscles 
comparable to the so-called interbranchiale of Chimaera. They 
represent the middle portion only of that muscle, and have 
acquired their actual position on their respective arches by 
passing over the posterior edges of those arches. They are 
thus not homodynamous either with the adductor of the man- 
dibular arch or with that of the hyoid arch. 
36. The levator arcus palatini and the dilatator operculi are, 
in Amia, as in teleosts, separate and distinct muscles. They are 
developed from a single muscle derived from the dorsal half of 
the general constrictor of the mandibular arch. Their innervation 
and position indicate that they are, together, the homologue of 
the muscle called by Vetter, in selachians, Addy, and that they, 
and that muscle, arise from the dorsal portion of the inter- 
branchial muscle of their arch. They are thus homodynamous 
with the levator operculi, and not with the levators of the 
branchial arches. 
