116 Cc. H. DANFORTH 
hangs the muscle. Its fibers are very nearly vertical in position. 
The anterior are inserted in the groove in Meckel’s cartilage, 
medial to the insertion of the superficial division of the muscle. 
The posterior fibers are inserted (a) into the posterior part of 
the groove and (b) into the dentary bone. 
‘ Innervation. Both divisions are supplied by the inferior maxil- 
lary branch of the trigeminus which runs along the dorso-mesial 
side of the superficial part and crosses the lateral face of the 
deep part. The main branch to the former is given off near the 
middle of the muscle and is directed anteriorly. : 
Blood supply. The facial artery and facial vein supply both 
divisions. 
Action. The anterior portion, besides helping to close the 
mouth, must also tend to protract the mandible, since its pull 
is somewhat diagonally forward and upward. The deep part 
may tend in a measure to oppose its action as a protractor. 
Working together or separately they would close the mouth. 
In both origin and insertion this muscle corresponds fairly well 
with the adductor mandibularis of Acipenser. There, however, 
according to Vetter’s description, the muscle is a weak flat ele- 
ment which becomes tendinous towards its insertion. Some of 
the fibers are inserted on the mandible as in Polyodon. In 
Acipenser there is, in addition to the adductor mandibulae, a 
strong constrictor muscle (Cs., of Vetter) which overlies it. The 
latter arises from the antorbital process and extends around the 
lower jaw. ‘The anterior part of the adductor in Polyodon has 
a superficial resemblance to this muscle, but none of its fibers 
arise from any part of the cranium proper and I have been unable 
to find any indication that they ever pass over into the ventral 
constrictor below the jaw. Consequently, from adult material 
alone, it can not be stated with any certainty that the anterior 
adductor of Polyodon finds a homologue in the constrictor of 
Acipenser, although there is a possibility that such is the case. 
If not, then the constrictor is unrepresented in Polyodon and 
the adductor is somewhat more specialized. In comparison with 
the adductor muscles of Amia and the teleosts that of Polyodon 
is remarkably simple. 
