Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 8l 



is, as already stated, thickened and runs 'downward and backward 

 to the anterior edge of the basisphenoid. Starting from the ante- 

 rior portion of the olfactory extension of the cranial cavity there 

 are always, in the interorbital membrane, fibrous lines, which run 

 downward and forward toward the ventral process of the antor- 

 bital cartilage, and there gradually disappear. In many of the 

 specimens examined, a small opening pierced the septum, imme- 

 diately in front of these fibrous lines. It did not seem to have 

 been artificially produced, in. any of the specimens where it was 

 found, but it seemed to have no relation whatever to any of the 

 orbital structures. 



The optic nerves, as already stated, pierce the hind edge of the 

 interorbital septum immediately in front of the basisphenoid ; and 

 about midway between these nerves and the hind end of the mem- 

 branous olfactory chamber, the eye-stalks have their origin, aris- 

 ing from a semicartilaginous nodule in the thickened hind edge 

 of the septum. The eye-stalk, on each side, runs forward and 

 laterally, along the dorso-anterior surface of the opticus, and is 

 inserted on the eye-ball close to the place where the opticus enters 

 it. In section the eye-stalk is round. It has a tough, fibrous, 

 peripheral covering, and a somewhat gelatinous interior which 

 resembles, in general appearance, the tissue that fills the spaces 

 between adjoining vertebrae. In alcoholic preparations the entire 

 stalk becomes semi-cartilaginous in appearance. 



From the anterior part of the interorbital septum, immediately 

 in front of the fibrous lines that run downward and forward from 

 the olfactory extension of the cranial cavity, the obliqui muscles 

 have their origin. The surface of origin of these muscles is oval, 

 with its long axis directed upward and backward, and it Hes imme- 

 diately ventral to that part of the olfactorius that lies free in the 

 orbit. As the muscles arise entirely from the interorbital mem- 

 brane, the existence of an anterior eye-muscle canal in Scomber 

 may perhaps be questioned, although the large recess that lies 

 between the septum and the orbital rib of the preorbital ossifica- 

 tion, or the smaller ventral part alone of that recess, occupy the 

 position of such a canal. If this recess is the representative, in 

 Scomber, of the so-called anterior eye-muscle canal of certain 

 teleosts, it is evident that the canal must, in this fish, owe its origin 



