ORIGIN OF JAW APPARATUS 345 
The anatomy and histology of these structures is quite fully 
described in the literature of Amphioxus. 
The two mesial tentacles at the base of the jaw bars differ 
from the others in being shorter and broader and they leave the 
k ie 
y 
f 
A. 
pie MI 
Fig. 2 Ventral view of the median part of the right and left jaw bars of Am- 
phioxus. A shows the usual symmetrical arrangements of the tentacles on the 
bar. B shows an irregular arrangement; r and J are the first tentacular rods 
given off from the right and left jaw bars. 
center of their basal plates, not at the anterior (distal) border 
as is the case with all the others. They have the appearance 
of palps. 
The oral hood has the following attachments: 1) Directly 
continuous with the metapleural folds. 2) Strong tendinous 
attachment along the dorsal longitudinal lines of contact with 
