Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 117 



ribs of Anita be true upper ribs, as I was led to suggest in an 

 earlier work (No. 4, p. 715), the horizontal ribs of Scomber would 

 naturally be the homologues of the ribs of that fish, as their serial 

 relations to the occipito-supraclavicular ligament indicate. In 

 Monacanthns, Goeppert says there are no ventral ribs (Pleural- 

 bogen), that fish differing radically in this from Scouiher. 



3. The Visceral Arches. 

 I. Gill Filaments. 



Scomber has four branchial arches, each with a double row of 

 gill filaments, a fifth incomplete arch, without gill filaments, and 

 an opercular demibranch. 



The opercular demibranch lies near the dorsal end of the inner 

 surface of the gill cover, partly on that cover and partly super- 

 ficial to the thick hind edge of the adductor hyomandibularis mus- 

 cle. The anterior end of its ventral edge lies immediately above 

 the proximal and dorsal end of the infrapharyngobranchial of 

 the first arch. From there the ventral edge of the gill extends 

 at first outward and backward slightly dorsal to the ventral edge 

 of the wide posterior surface of the adductor hyomandibularis, and 

 then, beyond that muscle, upward and backward along the inner 

 surface of the operculum. From this curved ventral line the fila- 

 ments of the demibranch extend upward and slightly backward, 

 being longest in their middle portion and thus giving to the whole 

 structure a somewhat oval form. The demibranch covers almost 

 completely the thick, posterior surface of the adductor hyomandi- 

 bularis, and, beyond that muscle, a part of the inner surface of 

 the operculum. It is attached (Fig. 39) to the mucous mem- 

 branes that cover the muscle and the operculum, the surface of 

 attachment being so wide that the ventral halves, approximately, 

 of the filaments are included in it. The dorsal halves of the fila- 

 ments are thus the only parts left free, the demibranch resembling, 

 in this, but not in its surface of attachment, the demibranch of 

 Salnio salar (No. 45, p. 243). 



The gill filaments of the demibranch, and also those on all 

 the branchial arches, all contain a central, bony, supporting ray. 

 These rays (Fig. 44) are V^-shaped at their proximal ends, the V 



