— 42 — 



cavity, forms the dorsal portion of the anterior wall of the labyrinth recess. The posterior recess on 

 the internal surface of the bone thus forms part of the labyrinth recess, but it lodges, in the adult, 

 no part of the membranous ear, lying wholly dorso-anterior to the curved anterior edge of the anterior 

 semicircular canal. The anterior recess forms the latero-postero-dorsal corner of that part of the 

 cranial cavity that lies between the labyrinth and fore-brain recesses, and would accordingly seem to 

 be a mid-brain recess. 



Ridewood says ('04a, p. 56) that the sphenotic is found distinct from the postfrontal in but 

 a few fishes. I, on the contrary, find these two bones almost invariably distinct and separate. Ride- 

 wood further says that the sphenotic is an endosteal ossification ,,set up in sympathy with" that 

 ossification in the dermal tissues that gives origin to the postfrontal; and he accordingly considers 

 the name sphenotic redundant. This relation of these two bones to each other I do not consider as 

 established. 



In the Barbidae, according to Sagemehl ('91, p. 573), the anterior semicircular canal may 

 be enclosed in a canal in the sphenotic. This semicircular canal thus has this relation to the sphenotic 

 in the Barbidae, while in Elops, as I have already stated, it traverses a canal in the alisphenoid. 



Swinnerton, in his descriptions of Gasterosteus, uses the term „postorbital process" in a 

 manner that might be confusing. On p. 532 of his work on that fish he says „the postorbital process, 

 which in other teleosts forms part of the alisphenoid, remains unossified". The process of Gasterosteus 

 here referred to is an outgrowth of the auditory capsule which projects forward in the dorsal portion 

 of the hind end of the orbit, and is accordingly more properly an orbital or supraorbital process, than 

 a postorbital one; and it is the lateral corner of its base, alone, that is the postorbital process, as that 

 term is commonly used, and it ossifies in Gasterosteus, as in other fishes, as the sphenotic. 



BASISPHENOID. 



The basisphenoid is, as usual, T-shaped, the ventral end of its pedicle abutting against a 

 median nodule of cartilage that lies on the dorsal surface of the parasphenoid. The anterior edge 

 of the pedicle is strongly curved, running at first forward and downward, or sometimes even directly 

 forward, and then curving downward, and downward and backward. The dorsal portion of the 

 pedicle is usually expanded into a relatively large median plate, and this part of the pedicle is often 

 independent of the ventral portion, touching and being bound to that portion, but not being con- 

 tinuous with it; the pedicle of the bone thus being in two, and sometimes even in three separate 

 pieces. The pedicle, as usual, separates the anterior opening of the myodome into two parts, and 

 its anterior edge gives insertion to the hind edge of the ventral portion of the membranous posterior 

 portion of the interorbital septum. 



The body of the basisphenoid is almost flat, and occupies a nearly horizontal, transverse 

 position. Its posterior edge, on either side, is overlapped ventrally by, and lies against the dorsal 

 surface of a small process of the prepituitary portion of the mesial process of the proötic, these small 

 prepituitary processes of the proötics of opposite sides meeting in the middle line and thus shutting 

 off the basisphenoid from the anterior edge of the pituitary opening of the brain case. In Scomber 

 (Allis, '03), the basisphenoid forms part of the anterior edge of the latter opening. In Amia the 

 anterior edge of the opening is formed by a transverse bolster of cartilage, the actual anterior edge 

 of the pituitary fossa being, however, formed of membrane only. 



