250 EDWARD PHELPS ALLIS, JR. 
and, projecting dorso-anteriorly, extends approximately to the 
transverse plane of the anterior edge of the hypophysis, where 
it reaches to about the middle of the height of the myodome. 
The large membranous pituitary sac rests upon its dorsal sur- 
face, that surface being presented dorsoposteriorly. The space 
beneath this ridge opens anteriorly into the subpituitary por- 
tion of the myodome. 
The ascending processes of the parasphenoid have their 
greatest dorsal extent anterior to the transverse ridge on its 
dorsal surface, and Swinnerton says that these processes of 
Gasterosteus are not the homologues of the processes of the 
bone of Amia. Swinnerton based this conclusion wholly upon 
the fact that each process of the bone of Gasterosteus lies ante- 
rior to the foramen for the nervus trigeminus, while in Amia 
it lies posterior to it; but he overlooked the fact that a part of 
the process of Gasterosteus, as shown in his figure 19, plate 29, 
projects dorsally posterior to the foramen trigeminum, this 
part of the process thus corresponding to the process of Amia. 
The anterior portion of the process of Gasterosteus lies lateral 
to the oculomotorius, trochlearis, and profundus nerves, and 
also lateral to the vena jugularis and the rectus muscles, be- 
tween them and the nervus trigeminus, thus having exactly 
the relations to these several structures as does the pedicel of 
the alisphenoid bone of Amia. This part of the process of Gaster- 
osteus thus replaces functionally a pedicel of the alisphenoid, 
and it has certainly been developed in relation to tissues that 
represent, in this fish, that bone of Amia. The orbital open- . 
ing of the myodome of Gasterosteus thus differs from the open- 
ing in all the other fishes so far considered, except Cottus and 
Clinocottus, in which latter fishes the pedicel of the alisphenoid 
of Amia is also represented by a process of the parasphenoid. The 
orbital opening of the myodome of Gasterosteus, and also that 
of Cottus and Clinoccottus, does not, however, correspond 
strictly to that of the myodome of Amia, for, as will be shown 
later, there has been added to its ventral portion the canals 
traversed, in Amia, by the internal carotid arteries and the 
palatine branches of the faciales. 
