348 HOWARD AYERS 
section through the sagittal plane of the body. It will be noted 
how the ventral transverse muscle thickens as it approaches 
the base of the jaw bars, also how bundles of muscle fibers take 
on a longitudinal direction to insert on the jaw bars. Two large 
muscles and one small one which surround the base of the jaw 
follow the bars forward as the main intrinsic muscles of the 
jaw bars. The largest and most caudad of the three is seen to 
contain a large element of transverse fibers — the anterior bundles 
Fig. 5 Dorsal view of dissection of jaw base and ventral floor of velar cham- 
ber and endostyle of Amphioxus, showing the muscles attached to ventral sur- 
face of anterior end of endostyle arising out of the transversus and the lateral 
lines of attachment of endostyle to sheath of the transverse muscle. 
of the transverse ventral muscle. One longitudinal bundle 
is shown which originates from the base of the endostyle and 
ventral border of the velum. In figure 2 is indicated the inter- 
digitation and the crossing of these three bundles at the base 
of the jaw bars. In figure 4B and figure 5 is shown the bundle 
which arises from the base endostyle and velum. 
In figure 6 the manner of origin of the left half of the jaw 
muscles from the transverse muscle to the left of the median 
line is indicated. Figure 7 shows a dissection of the jaw muscles, 
