— 38 — 



There are thus, on the lateral surface of the skull of Scorpaena, two separate depressions in 

 eaeh of which certain of the levator and adductor muscles of the visceral arches have their origins, 

 and the anterior one of the two seems certainly to have been developed in some relation to the 

 muscles that have their origins in it. With the posterior depression, this causal relation is rauch less 

 evident, and it would seem as if the anterior depression of Scorpaena must be superimposed upon 

 the posterior one to form the subtemporal fossa of Sagemehl's and Ridewood's descriptions of the 

 Cyprinidae. Sagemehl says that this fossa in these latter fishes is formed as the result of the origins 

 of certain of the levator muscles on this particular part of the skull, and he says that, in the Barbidae, 

 the adductor operculi arises in the anterior part of the fossa, and the externa! levator of the fourth 

 arch in its posterior portion. Of the other Cyprinidae he simply says that the levators of the branch- 

 ial arches arise from the side walls of the skull below the adductor hyomandibularis and adductor 

 operculi. Ridewood says ('04 a, p. 62) that, in certain of these same fishes, the fossa serves ,,for the 

 lodgment of the great muscles, which by pulling up the inferior pharyngeal bones (fifth ceratobranch- 

 ials) bring the teeth upon those bones forcibly against the callous päd that is carried on the under 

 surface of the basioccipital bone"; and Vetter says ('78, p. 505) that, in Cyprinus and Barbus, the 

 levatores arc. branch. externi have their origins in part in this fossa, that they are in part inserted 

 on the hind surface of the outer corner of the large inferior pharyngeal bone, and that they press 

 that bone against the bony plate on the under surface of the basioccipital. It seems, accordingly, 

 to be to certain of the external levators alone that the fossa-forming quality is attributed, and when 

 they happen to have their points of origin on the side wall of the skull in the region of the sub- 

 triangular depression of Scorpaena, they apparently may cause a deepening of that depression and 

 so give rise to a true subtemporal fossa. The subtriangular depression of Scorpaena would accordingly 

 seem to be a rudimentary fossa, and may be called the subtemporal depression. In the Barbidae 

 and Homaloptera this depression is deepened to such an extent that the epiotic is seen at the bottom 

 of it (Sagemehl, '91, p. 554); while in Elops, according to Ridewood, the supraoccipital also is there 

 exposed. 



Immediately ventral to the surface of origin of the adductor hyomandibularis, on the dorsal 

 portion of the bulla acustica, a large bündle of the muscles of the trunk has its origin. 



THE ORBIT. 



The orbit is large. The interorbital septum is cartilaginous in its anterior and larger portion, 

 but membranous in its posterior portion. The ventral half of this membranous portion is attached 

 posteriorly to the anterior edge of the pedicle of the basisphenoid. Above the dorsal end of that 

 pedicle, the membrane spreads laterally, on either side, and is attached to the anterior edge of the 

 body of the basisphenoid, and, above that bone, to the ventral edge of the alisphenoid and then to 

 the ventral edge of the ventral process of the frontal; the membrane thus closing the orbital opening 

 of the brain case. This membrane is pierced, on either side, and immediately above the basisphenoid, 

 by the optic nerve. Slightly above the optic nerves, the two oflactory nerves enter a small median 

 pocket in the membrane, from which a membranous tube leads forward on either side of the inter- 

 orbital septum. Having traversed this tube, the olfactory nerve of either side continues forward, 

 in the orbit, lying along the lateral surface of the cartilaginous portion of the interorbital septum 

 and so reaches and then traverses the olfactory canal through the ectethmoid. Lateral to the olfac- 

 torius, and along, or enclosed in, the ventral edge of the alisphenoid, the trochlearis enters the orbit. 



