ANATOMY OF HETERODONTUS: ENDOSKELETON 465 
Extra-visceral cartilages. The visceral arches are provided 
with superficial pieces, the extra-visceral cartilages. These for 
convenience may be separated into the labial cartilages, the 
extra-hyoid and the extra-branchial cartilages. The labials 
are located at the sides of the mouth and consist of three pieces 
of cartilage on each side, two dorsal and one ventral (d.l.1-2 and 
v.l., fig.6). The posterior dorsal labial is about twice the length 
of the anterior dorsal labial cartilage; it articulates with the 
ventral labial at its distal end so that the two serve to reduce 
the gape of the mouth. 
An extra-hyoid cartilage, so far as I have been able to make 
out, is lacking dorsally, and the one which appears ventrally is 
small. This, in the adult, is generally a nodule of cartilage less 
than half the length of the one shown in figure 9. In all cases 
the extra-hyoid cartilage was located where the termini of the 
ventral aorta bifurcate to form the first and second afferent 
arteries, the body of it lying superficial to the base of the second 
afferent. In no case did I find it further out over the first gill 
pocket as is shown for Heterodontus philippi (Max Fiirbringer 
’97, pl. 6, fig. 5). In one of the cases examined the extra- 
hyoid on the right side was elongated as is shown in figure 9, 
while on the left it was a nodule very much like the enlarged 
end of the cartilage seen in figure 9. Usually both of the carti- 
lages were almost identical in shape with that figured by Gegen- 
baur and Karl Firbringer as the first basibranchial. I am at a 
loss to know whether what Gegenbaur described as a single 
piece and Fiirbringer described as paired cartilages are not in 
fact what I have regarded as the extra-hyoids. If these be the 
cartilages described by them I am convinced that they are not 
basibranchials since they lie entirely superficial to the second 
afferent artery. 
Extra-branchial cartilages are located over all of the (internal) 
branchial arches in Heterodontus excepting the fifth. The 
extra-branchials of the first branchial arch are usually large and 
like succeeding arches overlap terminally (ez.b., fig. 10). The 
first three cartilages are hook-shaped at their attached ends, the 
dorsal ones only slightly and the ventral pieces in a very pro- 
