2IO AYERS AND JACKSON. [Vol. XVII. 



bar, which becomes more slender posteriorly. After fusing 

 with the upper division of the second branchial it passes back- 

 ward and slightly upward, ending in a sharp apex just below the 

 posterior end of the superior lateral bar. Near the posterior 

 end the lower division of the second branchial arch begins 

 from the inferior margin and extends forward, downward, and 

 inward, to fuse with the posterior process {sb) of the second 

 segment of the nasal plate, as previously described. 



Lying in the median dorsal pharyngeal wall, between the 

 posterior portions of the superior lateral bars, is a flattened 

 plate, the suprapharyngeal cartilage (PI. XXII, Figs. 5, 6, S). 

 It is composed of a body and two lateral horns. The body 

 is a flattened, nearly circular plate, somewhat wider than the 

 notochord. The plate is usually perforated by two openings 

 lying one behind the other in the median line, but there is 

 considerable variation in different specimens. On each side 

 of the plate is given off a slender lateral horn which extends 

 outward and slightly downward, with a sharp apex ending free 

 near the tip of the superior lateral bar. The lateral horns are 

 continued anteriorly with the anterior connecting processes 

 {a) from the velar cartilages. From the body of the supra- 

 pharyngeal cartilage there is also given off anteriorly, in the 

 median line, a short process that fuses with the vertical median 

 connecting process (w), which passes directly downward to the 

 underlying velar cartilages. 



The velum, or pharyngeal valve, is formed by an evagination 

 of the mucous membrane from the dorsal and lateral walls of 

 the pharynx. The velum projects backward in the pharyngeal 

 cavity and is supported by a framework of velar cartilages. 

 This includes the external and internal lateral bars, connect- 

 ing bars, and connecting processes. The external lateral velar 

 bars (PI. XXII, Fig. 6 ; PI. XXIII, Fig. 7, V) are the largest 

 and support the lateral margins of the velum. Anteriorly the 

 bar is large, thick, strong, and flattened laterally. Posteriorly 

 it tapers very gradually to a point. The rod is slightly curved, 

 *the posterior end being nearer the median line. The anterior 

 end of the bar is continued into a large, strong, articular process, 

 extending outward and slightly downward. This process 



