OSTEOLOGY OF RHAMPHOCOTTUS 469 



The dentary (d.) is forked widely posteriorly; anteriorly it is 

 curved inward to join its fellow of the opposite side. The lower 

 limb of the posterior fork has a groove on its outer surface for 

 reception of the wedge-shaped anterior end of the articular bone. 

 The superior liinb curves upward and its posterior part is wide 

 and flat. The superior edges of the dentary bones are beset 

 with rows of villiform teeth as shown in figure 13. 



The maxillary apparatus consists of a pair each of maxillae 

 and premaxillae. 



The maxilla (m.) is a rather strong rod of bone, the inferior 

 end of which is produced as a flat, paddle-like process. The 

 superior end is expanded to form a rounded knob w^hich is at- 

 tached to the shaft of the bone by a distinctly grooved neck, 

 which bends posteriorly at a right angle to the main part of the 

 bone (fig. 9). 



The premaxillae (pin.) are firmly united along the median line 

 by synchondrosis. Anteriorly they form a curved expansion of 

 bone, the under or convex surface of which is thickly covered 

 with villiform teeth. From the expanded anterior part of the 

 bone a slender rod of bone extends posteriorly in a groove between 

 the nasal spines (figs. 4 and 9). In the living specimen the pre- 

 maxillae are highly protractile. 



The opercular apparatus is made up of operculum, preopercu- 

 lum, and interoperculmn. A suboperculum is absent. 



The opercidum (op.) is slightly convex on its lateral surface 

 and is triangular in its general outline. The anterior angle of 

 the bone is considerably thickened and articulates by a distinct 

 facet with the opercular process of the hyomandibular (figs. 4 

 and 13). 



The small and flattened interoperculum (iop.) is coossified with 

 the inferior angle of the operculum. A slender process of the 

 bone extends downward for a short distance, medial to the inferior 

 arm of the preoperculum, and is connected by a slender ligament 

 with the angle of the mandible (fig. 13). 



The preoperculum (pop.) is the largest of the series. Its pos- 

 terior angle is produced as a long sharp spine. The general form 

 and connections of the bone are shown in figure 13. 



