— 165 — 



The ALISPHE.XOID, as seen from the outside of th(! skull, is a sub-semicircular bone, the 

 curved edge directed ventrally and deeply notched to form the superior border of the optic fenestra. 

 Immediately anterior to this fenestra, the ventral edge of the bone suturates with the dorsal edge 

 of the middle region of the interorbital process of the parasphenoid, while anterior to that region of 

 sutural contaet it is in synchondrosis with the cartilage of the interorbital wall. Posterior to the 

 optic fenestra it suturates with the proötic, the hind corner of the bone being in synchondrosis with 

 a small interspace of cartilage that lies between it and the proötic and sphenotic. On the internal 

 surface of the bone there is, as in the other fishes of the group, a large brace-like process which 

 separates the niid-brain and fore-bräin recesses of the cranial cavity. The dorsal edge of this process 

 is greatly expanded, as is also the dorsal edge of the bone itself, the large flat surface thus formed 

 giving Support mainly to the frontal; but the hind corner of the brace-like process extends backward 

 beneath the anterior edge of the supraoccipital and so gives support to that bone also. 



The alisphenoid is perforated, in the adult, immediately posterior to the optic fenestra, by 

 a s-nall foramen which doubtless transmits the nervus trochlearis; that nerve traversing the optic 

 fenestra, close against the alisphenoid, in 5 cm specimens. Near its dorsal edge the bone is traversed 

 by a small canal which transmits a brauch of the orbito-nasal vein, accompanied by a general 

 cutaneous brauch from the r. oticus trigemini. The bone is not traversed, as it is in the other fishes, 

 by the lateralis brauch that innervates the terminal organ of the supraorbital canal, that branch 

 passing upward external to the alisphenoid and then perforating the frontal. 



The SPHH.XOTIC isasmall and irregulär bone and is, in all my specimens, inseparably ankylosed 

 with the postfrontal, which latter bone lies upon and occupies about one half of the dorsal surface 

 of the sphenotic. The remainder of the dorsal surface of the sphenotic gives support mainly to the 

 pterotic, a small corner only of the bone supporting the hind edge of the frontal. In the fusion of 

 the sphenotic with the postfrontal, Dactylopterus resembles Polypterus, which latter fish is the 

 only other one in which, as I have stated in a recent work ('04, p. 56), I know this fusion to be of 

 regulär occurrence. Ridewood, since the publication of that work, has said ('04a, p. 56) that the 

 fusion of these two bones is also of almost constant occurrence in Amia, their Separation in that fish, 

 being an ,,occasional feature only". While this may be true of alcoholic or otherwise preserved speci- 

 mens, it certainly is not of fresh material. 



The sphenotic is in sutural contaet with the jsroötic and pterotic but not with the alisphenoid, 

 being separated from the latter bone by a small interspace of cartilage. On the lateral edge of the 

 bone there is a stout process which gives articulation to one of four articular processes on the dorsal 

 end of the hyomandibular, the particular process here concerned apparently being the regulär anterior 

 articular head of the hyomandibular, as will be later explained. Immediately dorsal to this articulating 

 process there is, on the same edge of the sphenotic, a sharp process which gives support, on its lateral 

 surface, to the small postorbital bone; probably also giving insertion to a part of the levator arcus 

 palatini muscle, though this was not investigated. 



Between the sphenotic and pterotic there is a large and deep dilatator fossa, roofed by the 

 pterotic and sphenotic, the postfrontal apparently not Coming into roofing relations with it. The 

 anterior wall of the fossa is perforated by a large foramen which transmits the ramus oticus. 



The l'ROÖTIC is a large bone with orbital and lateral portions, these two portions being 

 separated from each other bv a tall and ridgc-liko edge which, because of the flattened condition 



