No. 2.] MORPHOLOGY OF THE MYXINOIDEI. 203 



faint indication on the dorsal side. This anterior fused portion 

 is divided by a transverse suture which is concave forward, and 

 is well marked on the ventral side, but less distinctly on the 

 dorsal side. In the posterior third, the inner pair of bars 

 diverge slightly, enclosing in the angle between them the ante- 

 rior half of a diamond-shaped space. The posterior ends are 

 attached to the inner thirds of the anterior ends of the median 

 cartilages {Me). At the anterior end, the inner bars, just in 

 front of the fused portion, are extended outward, forward, and 

 upward as a pair of short, flattened processes. The flattened 

 inner bars are not placed in the horizontal plane, but are in- 

 clined toward each other so that a dorsal groove is formed by 

 their meeting in the median line. This groove is shallow pos- 

 teriorly but deeper anteriorly. In it the median portion of the 

 overlying dental plate glides. The anterior continuation of 

 this groove is formed by the anterior processes, whose faces 

 look forward, as well as upward and inward. An anterior 

 notch is thus formed, through which the tendon of the pro- 

 tractor muscles of the dental plate glides. The outer pair of 

 bars belonging to the anterior segment is larger, thicker, and 

 stronger than the inner (PI. XXIII, Figs. 8, 9, Ac). They are 

 somewhat flattened dorso-ventrally, and are wider at the ante- 

 rior end. Their posterior ends are attached to the outer two- 

 thirds of the anterior ends of the median cartilages, besides the 

 posterior ends of the inner pair. Anteriorly, the outer bars at 

 first diverge laterally and then curve inward slightly toward the 

 anterior ends, which are truncated and lie a short distance in 

 front of the anterior ends of the inner bars. The external 

 angles of the anterior ends give attachment to the lateral labial 

 cartilages {Lc). The outer bars are separated from the inner 

 pair by a narrow longitudinal slit. The ventral surfaces of the 

 outer bars are convex, the dorsal surfaces nearly plane. The 

 latter are inclined so as to be nearly in the same plane as the 

 corresponding inner bar, so that they aid in forming the grooved 

 dorsal surface on which the dental plate glides. The outer 

 bars are nowhere directly connected with the inner, the two 

 being bound together by strong ligamentous bands. The mid- 

 dle segment, B\ of the basal plate lies immediately behind the 



