Nos. iAxXD2.] AX ATOMY OF SCOMBER SCOMBER. 53 



The Orbits are large, occupying sometimes one half the length 

 of the skull. They are separated from each other, throughout 

 nearly their whole extent, by membrane only, there being no inter- 

 orbital ossification whatever, excepting only the small basisphe- 

 noid, and the interorbital cartilage being reduced to small rem- 

 nants at the base of the basisphenoid and at the anterior ends of 

 the mid-dorsal and mid-ventral lines of the orbit. These greatly 

 enlarged orbits cut into the skull to such an extent that an anterior 

 surface is formed to the brain case. This surface, on each side, 

 is presented forward, downward and but slightly outward, is rela- 

 tively flat, and forms the hind wall of the orbit of its side. Its 

 lateral edge is formed by the antero-lateral edge of the postorbital 

 process and by the anterior edge of the wing of the parasphenoid, 

 and it is deeply notched at about the middle of its length, the 

 nervi trigeminus and profundus, and the associated branches of 

 the lateral sensory nerves, there entering the orbit. 



The Choxdrocranium has either disappeared or been almost 

 entirely ossified, excepting in the antorbital region. In the post- 

 orbital region nothing remains of it but several relatively unim- 

 portant nodules and interspaces of cartilage, and the several nar- 

 row lines extending from them between the adjoining edges of the 

 neighboring bones. The cartilage seems, in certain parts of these 

 separating lines, to be replaced by a dense connective tissue, and, in 

 others, to have entirely disappeared, the bones in the latter places 

 being apparently directly connected by suture. These sutural con- 

 nections are usually formed by splint-like processes which project 

 from one bone and overlap and fit into corresponding depressions 

 on the outer surface of the other. The processes may, however, 

 arise from both bones, in which case they interlock. Similar 

 sutural connections may also be found even where the bones, in 

 their deeper parts, are still wholly separated by cartilage, the splint- 

 like sutural processes, in such cases, arising only from the denser, 

 superficial layers of the bones concerned. As these sutural proc- 

 esses are usually thin and semi-transparent, the lines of cartilage 

 or tissue separating the deeper parts of the bones can, in most 

 places, still be seen through them. 



In seeking to determine what parts of these separating lines were 

 formed of cartilage, stainings with reagents proved most unsatis- 



