48 ALUS. [Vol. XVIII. 



Osteology. 



The complete skeleton of the head of Scomber (Fig. 4) is 

 pointed, anteriorly, and is, both in lateral and dorsal views, some- 

 what triangular in general outline. In dorsal views it is about 

 twice as long as it is wide in its widest part, while, in lateral views, 

 it is less than once and a half as long as it is tall. In its ventral 

 portion it is much compressed, the inferior edges of the mandi- 

 bular and opercular bones almost meeting in the mid-ventral line. 

 It is accordingly, in transverse sections, somewhat triangular in 

 outline, the point of the triangular being directed downward. The 

 opercular bones are large, and their inferior edge, which is nearly 

 straight, forms nearly one half of the ventral edge of the skeleton. 

 The hind end of the mandible lies somewhat behind the middle 

 point of this ventral edge, and the height of the complete skeleton 

 at this point is nearly three times the height of the skull proper 

 in the same place. The skull proper, as here referred to, naturally 

 includes only those bones and cartilages of the head that are im- 

 movably attached together to form, in their posterior portion, the 

 brain case, and, in their anterior portion, the antorbital processes 

 and the rostrum. 



The bones of the skull of Scomber are all more or less soft and 

 tender, and this renders the deeper dissections of the head of the 

 fish particularly easy. Most of the bones are somewhat porous, 

 and the so-called primary ossifications usually contain, in pre- 

 served specimens, much fatty or oily matter, this being partic- 

 ularly noticeable in specimens that have been first treated in 



chromic acid. 



I. Skull. 



The Skull proper of Scomber (Figs. 5-10) is about twice as 

 long as it is broad, and nearly twice as broad, in its broadest part, 

 as it is deep at its hind end. Its hind end is, however, not its 

 deepest part, as the mid-ventral line of the skull is decidedly con- 

 vex and the deepest part of the curve lies approximately opposite 

 the base of the postorbital process. The skull has, thus, its great- 

 est depth at or near the hind end of the orbit, and, in this plane 

 it is, on its dorsal surface, nearly as broad as it is at its hind end. 



The mid-dorsal line of the skull is nearly straight, and the 

 anterior half of its dorsal surface is relatively flat. On this part 



