634 
Ceratodus thus, in the foramina traversed by the ramus palatinus 
facialis and in the general course of that nerve, resembles Lepidosteus 
more than it does any other of the fishes above referred to, as it 
also resembles that fish in the absence of a myodome. 
Returning now to the palatoquadrate of Ceratodus, it is evident, 
as already assumed in this discussion, that the space enclosed between 
the so-called pars ascendens palatoquadrati and the plane of the foramen 
prooticum laterale is the homologue of the trigemino-facialis chamber 
of Amia, excepting only in that it is not connected ventrally with 
the pituitary fossa, resembling in this last respect the chamber in 
Lepidosteus and teleosts. The chamber in Ceratodus thus being homo- 
logous with that in Amia, it would seem as if its lateral wall must 
necessarily be homologous with the corresponding wall in the latter fish 
notwithstanding that this wall is currently considered to be, in the one, a 
part of the palatoquadrate and in the other a part of the neurocranium. 
The palatoquadrate is, in the youngest embryo of Ceratodus de- 
scribed by SEWERTZOFF, a simple rod of cartilage that extends from 
the lateral surface of the basal portion of the chondrocranium to the 
mandible. Its dorsal end, at this stage, is apparently the homologue 
of the processus basalis of my descriptions of other fishes, and this 
simple rod of cartilage represents the entire dorsal half of the cartilage 
of the mandibular arch. Pterygoid and palatine portions of the cartilage 
are wholly wanting at this stage, but Grem describes (p. 1124), in an 
embryo of stage 45, at the point where his processus anterior joins 
the trabecula, a slight process which he considers as a rudimentary 
and transitory processus pterygoideus. He says that it is related to 
the dermal pterygoid and to the rudimentary premandibular visceral 
pocket found by him in this fish, and so far as I can understand the 
descriptions and discussion he considers the process to belong to a 
premandibular arch that has not yet separated from the mandibular 
arch. The pars ascendens of the palatoquadrate is a later development, 
and there is nothing in Grei’s descriptions to show that it is the 
result of a definite and progressive outgrowth of the basal portion of 
the cartilage rather than a chondrification in situ, and independent of 
the palatoquadrate. 
The pars ascendens of the palatoquadrate of Ceratodus thus cer- 
tainly has no homologue in the palatoquadrate of ganoids and teleosts, 
and it seems equally certainly to have its homologue in the lateral 
wall. of the trigemino-facialis chamber of those fishes. If it be the 
