ORIGIN OF JAW APPARATUS 341 
terey, partly collected by myself and partly by Miss Julia Worth- 
ington, who generously placed her extensive collections including 
adults, larvae, and embryos at my disposal. 4) Bdellostomas 
from Cape of Good Hope, Myxine from Norway and Torres 
Straits, Hexanchus from Bay of Monterey, various Elasmo- 
branchs from Woods Hole and Trieste, Callorhynchus, Chimaera, 
several species of Urodeles both larval and adult, and several 
species of Anura both larval and adult. 
A discussion of the literature is reserved for subsequent 
publication. 
AMPHIOXUS 
Under the term jaw apparatus are included all the structures 
constituting the cirri or tentacular apparatus of Amphioxus 
as recorded in the literature of the lancelet—skeleton, muscles, 
nerves, etc. 
The jaw bars form the internal skeleton of the armature of 
the buccal aperture of the oral hood. They are two elastic 
chondral bars, one in the left lip, the other in the right lip of 
the mouth. Each bar is composed of from seventeen to twenty 
segments progressively smaller from the base behind to the 
terminal segment in front. Each segment is prolonged into 
a tapering filament or tentacle which projects from the distal 
end of each segment. 
The two jaw bars are bilaterally symmetrical and, seen from 
above, curve outward from the median line in a gentle curve, 
until about midway of their course, when they curve inward 
so that the tips lie side by side in the anterior pocket of the 
buccal cavity (fig. 1). Seen from the side, the bars curve dor- 
sad from the base and then ventrad, then dorsad again to form 
an open S-shaped figure. These curves have their part in the 
functioning of the jaw apparatus in opening and closing the 
‘mouth. Under varying pull of the muscles, the bars change 
their shape. 
Thus the bases of the bars lie in the ventral wall of the body 
and the tips lie close under the notochord. The buccal aperture, 
thus looks forward and downward; it is placed at an angle to 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 33, NO. 4 
