the maxillary. The premaxillary articulates by fibrous 

 tissue along the middle of the lateral surface of the pos- 

 terior arm with the medial surface of the upper portion of 

 the maxillary, while along the medial surface of its pos- 

 terior arm the premaxillary articulates through fibrous 

 tissue with its opposite member. The ventral arm of the 

 premaxillary articulates through fibrous tissue along its 

 posteroventral edge with the anterior edge of the maxil- 

 lary. There are usually five incisorlike teeth, decreasing 

 in size laterally, borne in shallow sockets along the an- 

 terior edge of the premaxillary. Behind and internal to 

 this outer row of teeth there are usually two additional 

 teeth, the more medial of the two being the largest, of a 

 size and shape similar to that of the large most medial 

 tooth in the outer row, and the lateral inner tooth similar 

 to the small outermost tooth in the outer row. The teeth 

 are replaced by new ones developing in new sockets 

 which have pores to the exterior just above and external 

 to the sockets of the outer row of teeth. After a new tooth 

 erupts through the surface of the premaxillary, it 

 gradually migrates slightly forward and downward to the 

 area of the socket of the older tooth which it is replacing. 



Maxillary. — A more or less heavy rectangular 

 bone, rounded ventrally and less so dorsally, and slightly 

 constricted above the middle region; articulates by fi- 

 brous tissue dorsally along the lateral surface of its round- 

 ed portion with the anterior end of the palatine, while 

 along the medial surface of its rounded portion it at- 

 taches to the lateral and ventral surfaces of the posterior 

 arm of the premaxillary. Ventrally the medial surface of 

 the maxillary articulates by tough fibrous tissue with the 

 lateral surface of the posterodorsal part of the dentary, 

 while along the middle of its anterior edge the maxillary 

 articulates by similar tissue with the ventral arm of the 

 premaxillary. 



Lower Jaw. 



Dentary. — The posterior end concave on the 

 medial surface to accommodate the anterior end of the 

 articular, which it broadly overlies laterally but only 

 slightly overlies medially and to which it articulates by 

 fibrous tissue; articulates anteromedially by fibrous tis- 

 sue to its opposite member in the midline and postero- 

 laterally by interdigitation with the small angular. Along 

 the posterodorsal region of its lateral surface the dentary 

 articulates by tough fibrous tissue with the medial sur- 

 face of the ventral portion of the maxillary. There are 

 usually five incisorlike teeth borne in shallow sockets 

 along the anterior edge of the dentary and usually a 

 single tooth behind and internal to the outer series, the 

 single inner tooth being of a size comparable to that of 

 the two larger more medially placed teeth in the outer 

 series. The lower jaw teeth have the same form as the up- 

 per jaw teeth and are replaced by teeth developing in the 

 same manner as described for the premaxillary. 



Articular. — More or less triangular in shape; 

 cartilage filled at its anterior end, where it is continuous 



with the remains of Meckel's cartilage; articulates by fi- 

 brous tissue dorsally, ventrally, and laterally with the 

 broadly overlying dentary, posteroventrally by inter- 

 digitation with the angular, and posteriorly at the groove 

 on its posterior edge with the knob at the anterior end of 

 the quadrate. The sesamoid articular is a small ossifica- 

 tion held by fibrous tissue to the region of juncture of 

 Meckel's cartilage and the anteromedial surface of the 

 articular. 



Angular. — A small block of bone; articulates by 

 interdigitation dorsally with the articular and anteriorly 

 with the dentary. Posteriorly the angular connects by 

 ligament to the anterior end of the interoperculum. 



BRANCHIAL APPARATUS. 



Hyoid Arch, Branchiostegal Rays, and Urohyal. 



Hypohyals. —-Both hypohyal elements well de- 

 veloped; dorsal hypohyal cartilage filled along its ven- 

 tral and posterior edges, the ventral hypohyal cartilage 

 filled at its dorsal and posterior edges. The dorsal and 

 ventral hypohyals articulate through cartilage with one 

 another and with the ceratohyal, while they articulate by 

 fibrous tissue anteromedially with their opposite mem- 

 bers, and in the case of the dorsal hypohyal with the an- 

 terior third of the first basibranchial, which is held 

 between the posterior halves of the medial edges of the 

 apposed dorsal hypohyals. The ventral edge of the ven- 

 tral hypohyal articulates by fibrous tissue with the 

 urohyal. In large specimens there is sometimes a slight 

 amount of interdigitation between the dorsal and ven- 

 tral hypohyals. 



Ceratohyal. — A large plate expanded posteriorly; 

 cartilage filled at its anterior and posterior edges; ar- 

 ticulates through cartilage anteriorly with both of the 

 hypohyals and posteriorly with the epihyal, the ar- 

 ticulation with the epihyal sometimes strengthened by 

 interdigitation in large specimens. The six branchios- 

 tegal rays articulate by fibrous tissue with the cera- 

 tohyal; the first two rays along the ventral edge of 

 the posterior half of the ceratohyal and the last four rays 

 to the posterodorsal edge of the ceratohyal and, in the 

 case of the uppermost one or two rays, to the lower lateral 

 surface of the epihyal. 



Epihyal. — Large; cartilage filled at its anterior and 

 ventral edges; articulates anteriorly through cartilage 

 with the ceratohyal, this articulation sometimes being 

 strengthened by interdigitation, while posterodorsally 

 it articulates by fibrous tissue with the interhyal. 



Interhyal. — Short, columnar; cartilage filled at its 

 dorsal and ventral edges; articulates by fibrous tissue 

 ventrally with the epihyal and dorsally with the car- 

 tilaginous plate between the symplectic and hyoman- 

 dibular immediately behind the posterior end of the sym- 

 plectic. 



