No. 2.] MORPHOLOGY OF THE MYXINOIDEI. 209 



immediately expanding into a broad plate which fuses anteri- 

 orly with the connecting piece from the pterygo-quadrate, as 

 previously described, and posteriorly, at the same level, with 

 the anterior end of the superior lateral bar (b). The hyoid 

 arch then narrows somewhat and continues outward and 

 downward, its anterior margin forming the posterior boundary 

 of the large circular fenestra (3). From the anterior margin 

 of the hyoid a short flattened oval process extends forward, 

 nearly to the center of this space. Inferiorly the hyoid arch 

 again broadens out, connecting anteriorly with the inferior 

 process of the pterygo-quadrate, and posteriorly with the in- 

 ferior lateral bar {b^). In the angle between the hyoid and the 

 inferior lateral bar a short process curves upward, backward, and 

 then slightly downward, ending freely in the large fenestra (4). 

 This fenestra is bounded anteriorly by the posterior margin of 

 the hyoid, above by the superior lateral bar, below by the 

 inferior lateral bar, and posteriorly by the upper end of the 

 second branchial bar (br^. The first branchial arch (PI. XXII, 

 Figs. 5, 6; PI. XXIII, Fig. 7, br^ is a slender cartilaginous 

 bar arising from the superior lateral bar at some distance 

 behind the hyoid. It curves at first outward, backward, and 

 downward, over the middle part of the fenestra (4), previously 

 described ; then it curves forward and inward to fuse with the 

 posterior process of the second basal segment {sb), together 

 with the lower end of the second branchial arch {br^. 



The superior lateral cartilage (Figs. 5, 6, 7, b) arising anteri- 

 orly from the upper portion of the hyoid arch, and continuing 

 directly backward, gives attachment externally to the first 

 branchial arch, as just noted. Then it continues horizontally 

 backward and finally curves slightly outward and downward, 

 broadening out into a flattened, somewhat triangular plate, 

 which terminates posteriorly in a sharp apex. The lower angle 

 of the triangle is continued into the upper division of the 

 second branchial arch (Figs. 5, 6, 7, br^. The upper division 

 extends downward into a more or less prominent process, then 

 turns sharply backward and fuses with the inferior lateral 

 bar {b). This bar, as previously noted, arises anteriorly from 

 the inferior portion of the hyoid, being at first a rather strong 



