114 Cc. H. DANFORTH 
at first suggest an intermandibularis, but in teleosts and Amia, 
where such a muscle is recognized, it is found to consist of fibers 
which lie close to the symphysis and pass from one ramus of 
the mandible to the other with no median interruption. Both 
of these characters indicate that the muscle in question is not 
a true intermandibular. Vetter (’78) quotes Stannius to the 
effect that the geniohyoid of Acipenser is supplied in part by 
the trigeminal nerve, which is in accord with conditions found 
here. The anterior part of the muscle seems to correspond with 
the ventral constrictor of Heptanchus which Vetter (’74) desig- 
nates as CSV,. The posterior part represents the superficial 
fibers immediately posterior to this. Such an interpretation 
seems the more probable when it is recalled that with the great 
development of the opercular folds which occurs in Polyodon 
the web of tissue connecting the two flaps ventrally is extended 
backward to a very marked degree (fig. 3). There is in conse- 
quence this extensive development of skin musculature repre- 
senting a transverse band which was primitively very much 
narrower. 
M. adductor mandibularis: figure 2, m.adm., m.adm.’ 
The M. adductor mandibularis is in two parts, a long rounded 
superficial portion (m.adm.), and a short flat mesial part (m.adm.’). 
These two elements are somewhat distinct but become confluent 
where in contact and especially towards their insertion. The 
superficial division arises on the dorsal surface of the palato- 
quadrate from the median line in front back to the middle of 
the cartilage. Anteriorly it is horizontal in position and occupies 
the space between the M. protractor hyomandibularis above and 
the palatoquadrate cartilage and maxillary bone below. Near 
the angle of the mouth it passes under a strong triangular fascia 
and turns abruptly downward to be inserted (a) in the anterior 
part of a broad shallow groove in Meckel’s cartilage, and (b) 
on the median aspect of the overlying dentary bone. The deep 
division of the muscle, which extends somewhat further caudad 
than the other, arises laterally from the posterior third of the 
palatoquadrate, but not from its lateral projection which over- 
