MYODOME AND TRIGEMINO-FACIALIS CHAMBER 263 
I have now reexamined my sections of young specimens of 
this fish, but the material was evidently not in a good state of 
preservation when sectioned, for the membranes in the myo- 
domic region are all more or less disintegrated. The cartilages 
I tentatively identified in my earlier work as trabecular and para- 
chordal are certainly those cartilages, as currently conceived, 
for the one lies wholly anterior to the hypophysis and the other 
along the lateral wall of, and posterior to, that organ. The 
anterior end of the parachordal cartilage is, as I stated, enclosed 
between external and internal plates of the parasphenoid, but 
neither plate is adherent to it, and, in the adult, the cartilage les 
in a little pocket on the dorsal surface of the parasphenoid and 
ean be easily withdrawn from it without breakage. Posterior 
to this pocket, the cartilage, in embryos, gradually becomes 
enclosed between plates of perichondrial bone which form part 
of the prootic, the internal plate of the parasphenoid gradually 
diminishing in height and finally vanishing. The ventral edges 
of the prootics form the lateral boundaries of the fenestra ven- 
tralis myodomus. The hypophysis is large, lies directly above 
this fenestra, upon the dorsal surface of the parasphenoid, and 
extends posteriorly to the anterior surface of the transverse 
bolster described in my earlier work. This bolster is but slightly 
developed in my young specimens, but it is evidently formed 
either by the fusion of the horizontal and ventral processes of 
the prootics or by the horizontal processes alone, the ventral 
processes of the prootics, in the latter case, here vanishing. The 
cavity described by MeMurrich (’84) in this bolster would then 
seem to represent the prootic portion of the dorsal compart- 
ment of a myodomic cavity. A ventral myodomic compart- 
ment is wholly wanting, for that part of the parasphenoid lying 
in the prootic region has certainly been developed in the skeletog- 
enous tissue which, in the other Teleostei described, forms the 
horizontal myodomic membrane, this part of the parasphenoid 
of Amiurus thus corresponding to the transverse ridge on the 
dorsal surface of the bone of Gasterosteus. This, then, accounts 
for the fact that both the internal carotid artery and the ramus 
palatinus facialis of Amiurus lie everywhere external to the para- 
