— 7 — 



Scorpaena, thiis seems to represent tho fused anterior portions only of the supratemporal grooves 

 of Scomber. The posterior portions of the grooves of the hitter fish must accordingly be looked for 

 elsewhcre in Scorpaena, and they would seem to be represented, in this latter fish, in two small 

 pockets, one on either side, which occupy what is, in appearance, the dorsal portion of the posterior 

 surface of the skull. The pockets lie on a dorsal, shelving portion of the posterior surface of the skull, 

 this shelving portion being separated from the portion ventral to it by a distinct angle, usually pro- 

 duced into more or less of a ridge. This ridge is transverse and nearly horizontal in position, corres- 

 ponds approximately to the hind edge of the dorsal surface of the skull of Scomber, and appears as 

 that edge of the skull of Scorpaena when the dermal bones are removed (Fig. 7). 



There are thus two hind edges to the supratemporal portion of the dorsal surface of the skull 

 of Scorpaena, an antero-dorsal one formed by the dermal bones, and a postero-ventral one formed 

 by the primary bones. The development of these two edges I have not attempted to investigate, 

 but the Space between them evidently represents the extent to which the trunk muscles have invaded 

 the dorsal surface of the skull in the supratemporal region. This supratemporal Invasion is distinct 

 from the one that enters the temporal fossa, and its extent, which varies greatly in different fishes, 

 seems to be in some way related to the development of the extrascapular bones and the latero-sensory 

 canals they carrj'. Where the mesial extrascapular elements are strongly developed, meet in the 

 middle line, or are fused with the parietals, the trunk muscles pass dorsal to the hind edges of the 

 bones and stop when, or before, they reach the commissural canal: while where the bones are feebly 

 developed, or not fused with the parietals, the invading muscles seem to push them apart, to pass 

 forward beneath them and the canal they carry, and then onward, dorsal to the more anterior bones. 

 To the first mentioned, and probably more primitive category belong Polypterus, Amia, Lepidosteus, 

 Dactylopterus, and all those teleosts in which the mesial extrascapular elements have fused with the 

 parietals (Allis, '04); while to the second category probably belong the larger number of teleosts, 

 Scomber being typical of the class. The line that marks, in fishes, the anterior limit of the surface of 

 Invasion of the trunk muscles, has been called by Sagemehl ('84b) the linea nuchae, and it forms, 

 in many fishes of the first above-named category, the apparent, and is usually there considered as 

 the actual hind edge of the skull. It is, however, in reality, the secondary hind edge of the skull, 

 the primary hind edge underlying it and being formed by the hind edges of the dorsal surfaces of 

 the primary bones of the skull. The possible presence of these two edges must always be borne 

 in mind, for it is of importance in comparisons of the region. 



In Scorpaena, the two little pockets, just above described, accordingly lie on what is probably 

 the posterior portion of the dorsal surface of the skull, and not on its posterior surface. The mesial 

 half of the floor of each pocket is formed by a part of the supraoccipital, the lateral half being formed 

 in part by the epiotic, and in part by the dorso-posterior surface of a flange of bone that projects 

 downward backward and mesially from the ventral surface of the parieto-extrascapular, not far from 

 its hind edge. This flange lies on the dorsal surface of the primary skull, and notwithstanding its 

 apparent origin from the ventral surface of the parieto-extrascapular should probably be considered 

 as a part of the dorsal surface of that bone. The apparent hind edge of the parieto-extrascapular, 

 of either side, projecting backward, forms the roof of the corresponding pocket, and the two pockets 

 are separated from each other by the spina occipitalis. A part of the epiotic, together with overlying 

 parts of the suprascapular and parieto-extrascapular, separate each pocket from the dorsal portion 

 •of the corresponding temporal fossa. 



