HYOMANDIBULA OF THE GNATHOSTOME FISHES 591 
said by Gegenbaur (I. c., p. 200) to be represented by a wholly 
independent piece of cartilage. 
No ligaments are shown, in any of the Batoidei, connecting the 
cartilages of the mandibular arch with the epihyal or ceratohyal, 
by either Gegenbaur, Parker or Gadow (’88), and no postspiracu- 
lar ligament, either inferior or superior, is shown by either of 
those authors. Both Parker and Gadow show a stout ligament 
connecting the ventro-anterior end of the hyomandibula with 
one or both of the mandibular cartilages, and Parker shows a 
stout ligament connecting the same end of the hyomandibula 
with the spiracular cartilage, called by him the metapterygoid. 
I also do not find an inferior postspiracular ligament in either 
Raia or Torpedo, but I find, in Raia radiata, the posterior wall . 
of the spiracular canal lined with a tough ligamentous tissue 
which is firmly and directly attached, ventro-laterally (distally), 
to the anterior portion of the external surface of the hyoman- 
dibula, while dorso-mesially (proximally) a smaller and less con- 
sistent extension of the tissue passes dorso-external to the vena 
jugularis and is attached to the lateral wall of the auditory cap- 
sule. In Torpedo ocellata I find the hook-like process of the 
hyomandibula similarly connected by ligament with the audi- 
tory capsule, the process and ligament together evidently being 
the homologue of the ligament alone of Raia. This ligament of 
the Batoidei is thus quite certainly the homologue of the superior 
postspiracular ligament of the Selachii, and, like that ligament, 
the probable serial homologue either of the Mm. interarcuales 
dorsales I or the dorsal interarcual ligaments of the branchial 
arches of those fishes. The hook-like process of the hyomandi- 
bula of Torpedo and the corresponding independent cartilage of 
Narcine are then either simply chondrifications of that ligament, 
as I have already suggested in an earlier work (01), or, and this 
seems much more probable, dorsal interarcual cartilages similar 
to those found in the branchial region. 
If the conditions as thus described in the Batoidei be com- 
pared with those in the Selachii, it seems quite unquestionable 
that the hyomandibula of the former can not be the homologue 
of that of the latter, and it seems equally unquestionable that 
