Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 73 



The fore-brain recess of the cranial cavity is Hmited dorso- 

 posteriorly by the epiphysial ridge. This ridge (epr, Fig. 8), 

 starting from the middle line of the head, runs backward and 

 laterally, on each side, its anterior surface being formed by the 

 anterior one of the two laminar plates that form the posterior arm 

 of the Y-shaped ridge of the frontal. The posterior surface of 

 the ridge is formed by the anterior, turned-down end of the small, 

 median, postepiphysial interspace of cartilage already several times 

 referred to. This cartilage fits into a depressed region formed, on 

 the ventral surfaces of the adjoining edges of the frontals, by 

 the spreading of the laminar processes that form the posterior 

 arm of the Y of either side. It is somewhat rectangular 

 in outline, is concave on its ventral surface, and strongly keel- 

 shaped on its dorsal surface, the edge of the keel lying in the 

 median plane of the head. It extends backward nearly to the hind 

 edges of the frontals, where it abuts, with a wavy, transverse edge, 

 against the anterior edge of the supraoccipital, the hind edges of 

 the frontals slightly overlapping the latter bone. The anterior end 

 of the cartilage is convex, or pointed, turns downward, sometimes 

 almost at right angles to the rest of the piece, and ends, some- 

 times at the free inferior edge of the epiphysial ridge, and some- 

 times near that edge but separated from it by a thin plate of bone 

 that projects backward from the summit of the ridge. At each of 

 the antero-lateral corners of the cartilage there is a lateral projec- 

 tion from .which a narrow line of cartilage extends outward along 

 the dorsal edge of the posterial arm of the slightly Y-shaped dorsal 

 end of the alisphenoid. At the base, or lateral end, of the posterior 

 arm of this Y of the alisphenoid the line of cartilage is continued 

 forward and mesially along the dorsal edge of its anterior arm, 

 and backward and laterally along its shank. At the lateral end 

 of the shank of the Y the line of cartilage joins another line which 

 edges the dorso-mesial edge of the postorbital ossification. Antero- 

 ventrally this latter line lies between the postorbital ossification 

 and the alisphenoid, soon becoming indistinct and fibrous in ap- 

 pearance. Posteriorly it forms a definite but narrow band along 

 the free, dorso-mesial edge of the postorbital ossification; and at 

 the hind end of that bone joins the small interspace of cartilage 

 that lies in the bottom of the temporal groove. This latter i;iter- 



