ORIGIN OF JAW APPARATUS 395 
form veil and smaller nets with their connecting strands, en- 
closing the structures in an Amphioxine plexiform nerve appara- 
tus, the character of which leaves no doubt of its ancestral origin. 
The labial cartilages of the cartilaginous fishes have attracted 
the attention of anatomists from the time of Cuvier, who held 
that they are related to the jaws and represent the maxillary 
and intermaxillary, among other bones of the fish head. J. 
Miiller held that they were aberrant structures and had no re- 
lation to the jaw structures or any part of the mouth. Geg- 
enbaur thought they were remnants of premandibular gill arches. 
It has been an open field for guessing. The latter view seems 
to be the one in favor, notwithstanding the fact that no traces 
of gills or nerves that could belong to such body segments have 
been. found. 
Excepting Ammocoetes and the Myxinoids, the Chimaeroids 
have preserved the Amphioxine jaw apparatus more completely 
than any other of the cartilaginous fishes. Callorhynchus and 
Chimaera serve to bridge over the gap between the Myxinoid 
and what we are pleased to call the Gnathostomes. In figure 
10 the relations of the parts of the skeleton of the jaw apparatus 
of Callorhynchus are shown, and in figure 30 those of the related 
Chimaera are displayed, both from the left side, for ready com- 
parison with that of Bdellostoma (fig. 25). It will be noted that — 
in Callorhynchus the mechanism is about as complete as in 
Bdellostoma. It consists of two well-defined cartilaginous jaw 
bars, marked 3, fastened to the hyoid below and just outside of 
the mandible, 3b. They run forward and upward to the sides 
of the nasal region, 4 and 8, where they are connected with 
the tentacular cartilages grouped lateroventrad of the nasal 
capsules. The tentacular cartilages of the third and fourth 
tentacles of Bdellostoma, which are placed opposite the middle 
and lower part of the buccal aperture (figs. 22 and 25), are here 
located with the cartilages of the first and second tentacles 
close about the nasal apertures, and they no longer extend out- 
ward as slender tentacular rods but lie in flaps of the skin and the 
large rostral snout. As in Bdellostoma, the distal part of the 
