468 SYDNEY E. JOHNSON 



The anterior arm of the hyomandibular extends downward and 

 terminates in an irregular articulation with the symplectic and 

 the metapterygoid. The outer or posterior fork is very strongly 

 developed and affords support for the upper end of the preoper- 

 culum. Just posterior to this fork is a short blunt projection 

 bearing a socket with which the anterior angle of the operculmn 

 articulates (figs. 4 and 13). 



The symplectic (sy.) is a thin crescentic lamina (fig. 8) bounded 

 on its concave anterior margin by the quadrate and the meta- 

 pterygoid, and on its posterior or convex margin by the preopercu- 

 lum and the hyomandibular. 



The quadrate (q.) is a fairly strong bone of roughly rectangular 

 form. The upper part is thin and membrane-like, but the lower 

 anterior angle is thickened and produced as a rounded knob (fig. 

 13), which gives attachment to the articular process of the 

 mandible (ar., fig. 13). It is bounded anteriorly by the ptery- 

 goid, superiorly by the mesopterygoid and the metapterygoid, 

 and posteriorly by the symplectic and the preoperculum. 



The metapterygoid (mpt.), the mesopterygoid (mspt.), and the 

 pterygoid (pt.) are delicate laminae of bone, the position and 

 boundaries of which are shown in figure 13. The pterygoid is 

 the strongest of the three; its lower part is wedge-shaped, while 

 the superior portion is considerably thickened and curves forward, 

 uniting by a wedge-like process with the palatine bone. 



The palatine (pa.) is irregular in form, having an enlarged 

 posterior part which articulates with the pterygoid as mentioned 

 above, and an anterior, slender, somewhat outwardly curved 

 process which extends almost to the vomer. The palatines bear 

 no teeth (fig. 13). 



The mandible consists of three bones (on each side), the ar- 

 ticular, the angular, and the dentary. 



The articidar (ar.) is a relatively strong bone, expanded pos- 

 teriorly to articulate with the quadrate and tapering to a sharp 

 point anteriorly where it unites firmly with the dentary. A 

 thin triangular process extends upward and outward, and a blunt 

 process, downward, from the posterior end of the bone. The 

 latter process gives attachment to the small and irregular angular 

 (an.) bone (fig. 13). 



