THE MYOLOGY OF POLYODON EZ, 
M. protractor hyomandibularis: figure 2, m.pro. 
Of the two muscles in connection with the hyomandibular 
apparatus the anterior resembles very closely the muscle in 
Acipenser designated by Vetter (’78) and Gegenbaur (’98) as the 
protractor hyomandibularis. It is a large muscle, which in Polyo- 
don arises in two separate parts, which soon unite. The smaller 
portion, whose fibers constitute the ventro-median part of the 
muscle, arise laterally on the cartilaginous base of the skull from 
a small area lying medial to the anterior opening of the facial 
canal, close to the roof of the mouth and immediately in front 
c.hyb. 3 m.bmd. 
m.5md’, a.br.a.2 a.br.a.1 
Fig. 3 Schema to show relationships of the branchiomandibular and sterno- 
hyoid muscles 
of the spiracular cleft. From below, its origin is concealed by 
the parasphenoid bone and the overlying cartilage. ‘The second 
and much larger portion of the muscle arises from the post- 
orbital process, from the side of the chondrocranium and from 
the overhanging supraorbital cartilage, nearly as far forward as 
the olfactory capsule. The most anterior fibers, which are some- 
what tendinous at their origin, are dorsal and medial to the 
eye. This muscle fills the angle between the hyomandibular and 
skull and presses against the membrane stretching across the 
