604 EDWARD PHELPS ALLIS, JR. 
lachian hyomandibula. No other cartilage related to the dorsal 
end of the hyal arch is described by Greil. 
From these several descriptions of embryos of Ceratodus il is 
certain that three, and practically certain that four, separate and 
independent cartilages may develop in the dorsal half of the hyal 
arch of Ceratodus, and as this corresponds exactly with the num- 
ber found in the dorsal half of the arch in the Batoidei there is 
certainly no reason to assume, either that the epihyal has here 
been broken up into several pieces, or that an epi-pharyngohyal 
has been broken up into any others than the two normal pieces. 
The cartilage Ph has exactly the relations to the auditory cap- 
sule, the vena jugularis, the arteria carotis interna (lateral dor- 
sal aorta) and the nervus hyomandibularis facialis that the hyo- 
mandibula of the Batoidei has to the same structures. As in 
those fishes, its lateral end is attached to the palatoquadrate, by 
ligament in young embryos but by fusion in older ones, and it 
lies dorsal to the dorsal end of the mandibular aortic arch, which 
is probably the relation of the hyomandibula of the Batoidei to 
that artery, but I could not control this in my two already partly 
dissected specimens of the latter fishes. 
This cartilage Ph is thus certainly a pharyngohyal, and, to- 
gether with its dorsal process, can properly be called the hyoman- 
dibula.. The dorsal process (Ia) has the same relations to the 
pharyngohyal, the vena jugularis and the nervus hyomandibu- 
laris facialis that the hook-like process of the hyomandibula of 
Torpedo has, and is quite certainly the homologue of that pro- 
cess and hence of the corresponding, independent cartilage of 
Narcine. It is accordingly quite certainly an interarcual car- 
tilage. The cartilage Ex lies lateral to the vena jugularis and 
posterior to the nervus hyomandibularis facialis, and, in Edge- 
worth’s figure 20, its ventral end is in contact with the lateral 
(distal) end of the pharyngohyal (Ph). In the adult it has been 
pulled away from the pharyngohyal by the great expansion of 
the trigemino-facialis chamber, but it is still attached, by its 
ventral end, to the hyosuspensorial ligament dorsal to the car- 
tilage Kh. It has accordingly all the relations to the other struc- 
tures of the hyal arch, so far as they are given, of an extrabran- 
