614 EDWARD PHELPS ALLIS, JR. 
Holostei and Teleostei (Allis ’11 a, p. 292); and in that the 
hyomandibula articulates, in Polyodon, in part with the 
lateral wall of that canal. There is, in the Chondrostei, 
not the slightest indication of even a rudiment, of a postfacialis 
articular head of the hyomandibula, the extrabranchial of 
the arch thus not so beimg accounted for. There is an 
interhyal, which is quite certainly the strict homologue of 
that found in the Teleostei. The symplectic is a large 
and independent cartilage which extends from the ventral 
(distal) end of the hyomandibula to the articular end of the pala- 
toquadrate, strongly attached to both those cartilages by liga- 
ments or ligamentous tissues, and, as in the Teleostei, it would 
seem as if it must have been developed from one or more of the 
middle branchial rays of the mandibular series. Its relations to 
the arteria hyoidea are the same as those of the symplectic 
process of the Teleostei (Allis ’11 a, p. 260), but its relations to 
the nervus facialis would seem, from van Wijhe’s (82) figures 
and descriptions, to differ, in both Acipenser and Polyodon, 
from those in the Teleostei, and even to differ from each other 
in Acipenser and Polyodon. 
In Polyodon I find the ramus mandibularis internus facialis 
traversing a little notch in the hind edge of the symplectic which 
is also traversed by the efferent hyoidean artery (Allis’11a, p. 286), 
the nerve thus lying external to the cartilage while dorsal to the 
notch, but internal to the cartilage when ventral to the notch, the 
notch thus appearing to represent the interval between two rays 
that have here fused to form the symplectic. Parker (’82) con- 
sidered the symplectic of Acipenser to be a piece segmented from 
the ventral end of the epihyal, the remainder of the latter ele- 
ment forming the hyomandibula and the pharyngohyal being 
wholly wanting. But this breaking up of any one of the four 
typical elements of a visceral arch into two or more pieces, and 
their perpetuation by inheritance, finds no support whatever in 
my work. 
In Acipenser, van Wijhe (’82) shows a small process project- 
ing upward on the lateral surface of the hyomandibula between 
the mandibularis and hyoideus branches of the nervus hyoman- 
