252 EDWARD PHELPS ALLIS, JR. 
ever, unquestionably related to the fact that the vena jugularis 
lies ventral (mesial) to the nervus facialis in Gasterosteus, while 
in the other fishes mentioned above, except Catostomus, it lies 
dorsal (lateral) to that nerve. In Catostomus the vein lies. ven- 
tral (mesial) to the nervus facialis but lateral to the nervus pala- 
tinus, this thus being a variation in the transformation of the 
primitive vena cardinalis anterior into a vena capitis lateralis. 
A delicate median vertical membrane separates the space 
beneath the transverse ridge on the dorsal surface of the para- 
sphenoid into lateral halves, this membrane being continuous 
anteriorly with the membrane that gives insertion to the rectus 
muscles. At its hind end this membrane ossifies as a short 
median ridge on the dorsal surface of the parasphenoid. 
The space beneath the dorso-anteriorly projecting ridge on 
the dorsal surface of the parasphenoid thus corresponds strictly 
to the ventral compartment of the myodome of the other Tele- 
ostei so far considered, but the roof of that compartment, which 
is of membrane in those other fishes, has here been ossified as 
part of the parasphenoid. The recti externi and the pituitary 
veins run posteriorly dorsal to this ridge, and hence lie in the dor- 
sal compartment of the myodome, the pituitary veins lying along 
the lateral surfaces of the pituitary sac, and forming, posterior 
to it, a large median sinus. 
Posterior to the hind end of the ventral compartment of the 
myodome, and hence posterior also to the ascending processes 
of the parasphenoid, a tall median ridge of the latter bone, flat 
on its dorsal surface, projects upward between the ventral ends 
of the ventral processes of the prootics, its dorsal surface there 
forming the floor of the dorsal compartment of the myodome. 
Up to this point the ventral processes of the prootics are wholly 
of bone, but cartilage now appears in their ventral halves, as 
shown in Swinnerton’s figure 35, plate 30. The hind end of 
the membranous pituitary sac is here cut in the sections. Pro- 
ceeding posteriorly, the median ridge on the dorsal surface of 
the parasphenoid gradually becomes wider, and, arching up- 
ward, projects into the myodome between the ventral ends of 
the ventral processes of the prootics. ‘The membrane which, 
