262 EDWARD PHELFS ALLIS, JR. 
AMIURUS 
In the adult Amiurus the myodome was briefly considered 
by me in my work on the mail-cheeked fishes, and I there said 
(Allis, 709, p. 200) that; 
In the anterior three-fifths, approximately, of its length, the ven- 
tral edge of the prootic does not meet its fellow of the opposite side, 
a wide hypophysial fenestra, closed ventrally by the parasphenoid, 
being left between the two bones. Posterior to this fenestra, the ventral 
edges of the prootics meet in the middle line, and the two bones there 
form, on the floor of the cranial cavity, a prominent transverse bol- 
ster which has closely the position of the cross-canal of Lepidosteus; 
and it is certainly in this bolster that MecMurrich found the small 
cavity that he considered to be a rudimentary myodome. 
In the specimens that I examined at that time I found but slight 
indication of this cavity, but I nevertheless considered it to have 
existed previously in the transverse bolster and to have been sup- 
pressed by invading growth of the surrounding cartilage. 
In my work on the pseudobranchial and carotid arteries of 
this fish, I said (Allis, 08 b, p. 259) that the external carotid 
artery 
does not apparently traverse a trigemino-facialis chamber, for al- 
though it would seem as if that chamber must be present in some form, 
there is no proper indication of but one cranial wall in this region, and 
that one wall would seem to be the inner wall of the chamber; for both 
the external carotid and the jugular vein lie external to it. 
It was further said (p. 259) that: 
The parasphenoid of Ameiurus is peculiar in that the base of the 
ascending process of the bone, which begins immediately posterior to 
the so-called orbitosphenoid, is formed of two plates which enclose 
within them the hind end of the Ssubopticus (trabecular?) bar of car- 
tilage. The bone is here apparently not of perichondrial origin, but 
the inner plate nevertheless lies internal to the cartilage of the skull 
and there forms part of the immediate bounding wall of the cranial 
cavity. Posterior to the hind end of the trabecular (?) cartilage there 
is, for a few sections, a vacant space between the two plates of the proc- 
ess of the parasphenoid, and then those plates, the inner one of which 
gradually diminishes in height, enclose the anterior portion of the 
prootic (parachordal?) cartilage. It is perhaps this portion of the 
bone of the adult that led Me Murrich to conclude that the basisphenoid 
was here anchylosed with the parasphenoid. 
