HYOMANDIBULA OF THE GNATHOSTOME FISHES 615 
dibularis facialis. Parker (’82) does not show this process in 
Acipenser nor does Bridge (’79) show it in Polyodon, but Bridge 
found a nodule of cartilage in Acipenser and a filament of carti- 
lage in Polyodon, both of which are said to lie in a groove on the 
lateral surface of the hyomandibula and which may accordingly 
represent the process of van Wijhe’s descriptions. In a single 
specimen of Polyodon that I have rather summarily examined I 
find the process on the mesial, instead of the lateral, surface of 
the hyomandibula, and it lies, as the process does in Acipenser, 
between the two branches of the mandibularis facialis. Bridge 
considered the little cartilage found by him to be a remnant of a 
branchial ray, and as he does not specify to which arch it belongs, 
it was undoubtedly considered by him to belong to the hyal arch. 
But if the little cartilage is the homologue of the process described 
by van Wijhe it would seem as if it could not be a branchial ray 
of the hyal arch, for the process lies anterior to the ramus hyoid- 
eus facialis instead of posterior to it, as it normally should if it 
were aray of the related arch. Its relations to the afferent artery 
of the arch are not given, but it would seem as if it must lie an- 
terior also to that artery, which would not be normal. It cer- 
tainly lies dorso-posterior to both the afferent and efferent man- 
dibular arteries. It may accordingly be the extrabranchial of 
the mandibular arch; and as there seems to be no trigemino- 
facialis chamber in this fish, that element of the mandibular arch 
would be thus accounted for. Bridge describes, in Polyodon, a 
ligament which he calls the metapterygoid ligament and which 
he says extends from near the dorsal end of the hyomandibula, 
to ‘‘the smaller of the two parasphenoidal alae,’’ passing upward 
and forward ventral to the spiracular canal. This ligament ts 
said to support, on its spiracular surface, the short branchial fila- 
ments of the mandibular gill, and it hence corresponds, in posi- 
tion, to the spiracular cartilage and the related ligament and 
chain of little cartilages in Torpedo. There is, however, no 
spiracular cartilage related to it. 
In Polypterus the hyomandibula differs in certain important 
respects from that both of the Chondrostei and Teleostei, and, as 
in the case of the Chondrostei, the conditions here need further 
