ORIGIN OF JAW APPARATUS 347 
of bundles of fibers turned in varying degrees out of the trans- 
verse direction of the fibers of the parent muscle bed. Thus 
all the jaw muscles may be said to have their origin from the 
ventral transverse muscle and to insert on the jaw bars and their 
Fig. 4 A. Composite section to show relation“ of jaw base to velum of Amphi- 
oxus when jaw apparatus is expanded. The first three consecutive divisions of 
the gut are shown. 8B, buccal cavity; vc, velar chamber; G, pharyngeal canal. 
B. Dorsal view of jaw base, velum, velar chamber, median part of gills, to- 
gether with median muscle which arises from the transversus ventrad of the 
velum. 
tentacular projections. The jaw muscles are divisible into two 
groups. The first group contains the muscles of attachment; 
the second group the intrinsic jaw muscles, yet the latter are 
in a way extensions of the former. In figure 3, the relations 
of some of these muscles are shown as they appear in median 
