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fenestration, in the prepared skull, leads from orbit to orbit, traversing the interorbital portion of 

 the cranial cavity. In the recent state, the fenestra of either side is closed by a membrane which 

 is pierced by the optic nerve as it passes from the cranial cavity to the orbit. The two fenestrae 

 are accordingly the optic fenestrae. 



The interorbital process of the parasphenoid of Dactylopterus would seem to be the homologue 

 of the median process of the same bone of Gymnarchus, as shown in Erdl's ('47) figures, which 

 process is considered by that author as the lower portion of the ala magna, and by Ridewood ('04b, 

 p. 198) as the basisphenoid. It seems also to be the equivalent of the basisphenoid of Ameiurus 

 ('Mc Murrich, '84), fused, perhaps, with the orbitosphenoid of that fish. It is apparently the homo- 

 logue of the median process of the parasphenoid of Peristedion, but enormously developed. That 

 it contains an originallv independent basisphenoid element, as its general relations would certainly 

 indicate, seems improbable, for even in 5 cm specimens there is no slightest indication of two inde- 

 pendent ossifications. In these latter specimens, the process is apparently wholly of membrane 

 bone, but it is in part formed by two thin laminae of bone which enclose between them a part of 

 the cartilage of the interorbital septum, much as the pedicle of the basisphenoid does in young 

 specimens of Scorpaena. 



Ventral to the optic fenestra, and, in most of my specimens, partly confluent with it, there 

 is a second large perforation of the posterior portion of the interorbital wall, this Perforation also 

 leading from orbit to orbit but not traversing any portion of the cranial cavity. This perforation 

 is bounded anteriorly by the hind edge of the interorbital process of the parasphenoid. Ventro-posteri- 

 orly it is bounded by a tall and thin ridge of bone which extends transversely across the dorsal sur- 

 face of the parasphenoid between the small and pointed ascending processes of that bone. This^ 

 ridge of bone projects dorso-posteriorly, suturates on either side with the anterior edge of the ventral 

 portion of the proötic and slightly also with the ventral edge of the orbital portion of that bone, but 

 between the two proötics presents a free dorsal edge. In the recent state, a membrane extends from 

 this free portion of the edge of the ridge upward and forward to the concave hind edge of the spreading 

 arms of the orbital portion of the interorbital process of the parasphenoid, the lateral edges of the 

 membrane, postero-ventral to those arms, being attached, on either side, to the mesial edge of the 

 nearly vertical orbital portion of the corresponding proötic. Against that part of this membrane 

 that lies between the orbital portions of the proötics, or immediately postero-ventral to it, lies the 

 pituitary body, the entire opening closed by the membrane, or at least that part of it that lies between 

 the proötics, accordingly being the pituitary opening of the brain case. The whole opening may be 

 referred to as that opening. 



The ventral one of the two usually confluent perforations of the interorbital wall of Dactylo- 

 pterus thus lies between a membrane that fills the pituitary opening of the brain case and a process 

 of the parasphenoid the dorsal end of which fulfils the function of a basisphenoid, if it be not in part 

 that bone. On the antero-dorsal portion of the osseous boundary of this ventral perforation of the 

 interorbital wall, and partly also on the ventral surface of the membrane that closes the pituitary 

 opening, a median vertical membrane has its attachment. Ventro-posteriorly this membrane becomes 

 less strong, and separates into two parts which spread to either side and are doubtless attached to 

 the parasphenoid, though this could not be satisfactorily determined in my material. The membrane 

 is thus a median vertical one which closes, more or less completely, the ventral perforation. On 

 the dorsal portion of this membrane, in 5 cm specimens, and directly opposite its fellow of the opposite 



