HYOMANDIBULA OF THE GNATHOSTOME FISHES 595 
independent structures in his specimens, and says that the lower 
end of the hyomandibula, called by Huxley the symplectic pro- 
cess, is articulated to the dorsal surface of-the tubercule, and 
that, as this tubercule gives attachment also to the hyosuspen- 
sorial ligament, the hyomandibula is thus indirectly connected 
with the ceratohyal. The nervus hyomandibularis facialis 1s 
said by him either to perforate the hind edge of the suspenso- 
rium or to issue between that hind edge and the anterior edge of 
the lower, process-like end of the hyomandibula, and this pro- 
cess-like end is said to be frequently found segmented off as a 
separate cartilage. In one of the several specimens examined 
by him, Ridewood (1. c., fig. 3b, p. 637) found a little cartilage 
imbedded in the hyosuspensorial ligament which he says may 
‘‘nossibly have the value of an interhyal;” this little cartilage 
having been described by Pollard (’94) one month before and 
also said by him to probably represent an interhyal (stylohyal). 
Pollard (1. ce.) concluded that Huxley’s hyomandibula was an 
opercular cartilage, and Fiirbringer (’04) is undecided as to 
whether it be such a cartilage (Kiemenstrahlenrudimente) or 
the homologue of the hyomandibula of other fishes. 
Ridewood, alone, of the several authors above referred to, calls 
attention to the fact that the point where the so-called hyoman- 
dibula is attached to the neurocranium is widely separated from 
the auditory capsule, “‘in the vicinity of which the hyomandibu- 
lar of fishes usually articulates.’’ This intervening part of the 
neurocranium is, in fact, a wide concave surface presented ventro- 
latero-posteriorly, with the foramen faciale lying near its lateral 
margin and the foramen for the vena jugularis in its antero-ven- 
tro-mesial portion. The vena jugularis, after issuing from its 
foramen, runs posteriorly along the lateral surface of the neuro- 
cranium in the large jugular groove of van Wijhe’s descriptions, 
which groove lies dorsal to the foramina for the glosso- 
pharyngeus and vagus nerves. 
In a badly preserved specimen of Ceratodus that I have, I 
find, on one side of the head, this so-called hyomandibula with 
its symplectic process, and the ventral end of the process articu- 
lates with a stout, and slightly biconcave cartilage which, in 
JOURNAL OF MORPHOLOGY, VOL. 26, NO. 4 
