ORIGIN OF JAW APPARATUS 349 
their relation to the transverse ventral muscle, the jaw bars 
and basal tentacular palps. 
The group of intrinsic jaw muscles has been previously de- 
scribed. It consists of a large fusiform bundle (outer muscle) 
running the entire length of the jaw bar of either side and a 
smaller muscle consisting of long bundles and short thin plates 
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Fig. 6 Dorsal view of dissection of jaw muscles of the left side arising from 
transversus. Amphioxus. 
of muscle fibers extending from one tentacular bar to the next one 
in front (inner muscle). These two groups we may call, one 
the mandibular muscle and the other the tentacular muscle. 
They are both complicated in their make-up. 
_ The rectus-abdominis portions of myotomes 1 to 4, and some- 
times myotome 5, are attached to the wall of the buccal cavity 
