Mandibular Region. 



Hyomandlbular. — Somewhat expanded dorsally, 

 but tapering to a stout shaft ventrally; cartilage filled at 

 its posterodorsal and anteroventral edges; articulates by 

 fibrous tissue dorsally with the longitudinal groove on 

 the ventral surfaces of the prootic and pterotic, while 

 posterodorsally the hyomandlbular abuts against and is 

 firmly held by fibrous tissue along the medial surface of 

 the elongate portion of the ventral flange of the pterotic. 

 Along the lower three-fourths of its posterior edge the 

 hyomandlbular articulates by fibrous tissue with the 

 preoperculum. Just posterior to the dorsal end of the 

 preoperculum, the ventral edge of the hyomandlbular is 

 thickened and bears a concavity with which the dorsal 

 end of the operculum articulates by fibrous tissue. The 

 anterior end of the hyomandlbular articulates variously 

 through cartilage and fibrous tissue with the metapter- 

 ygoid, symplectic, interhyal, and preoperculum. 



Quadrate. — Widest posteriorly, tapering to a knob 

 anteriorly for articulation with the articular in the lower 

 jaw; cartilage filled at its posterior edge; deeply cleft 

 along its lower posterior edge to accommodate the 

 anterior end of the symplectic; articulates by slight inter- 

 digitation dorsally with the ectopterygoid, while it ar- 

 ticulates by fibrous tissue posteriorly with the 

 metapterygoid and symplectic, both of which somewhat 

 overlie the quadrate. Ventrally the quadrate articulates 

 by fibrous tissue with the preoperculum. 



Metapterygoid. — Large; a more or less rounded flat 

 plate; cartilage filled at its anterior edge; articulates by 

 fibrous tissue anteriorly with the quadrate, posteriorly 

 with the interhyal and hyomandlbular; articulates by 

 slight interdigitation dorsally with the mesopterygoid, 

 anterodorsally with the ectopterygoid, and ventrally with 

 the symplectic. 



Symplectic. — Large; cartilage filled at its anterior 

 and posterior edges; dorsally expanded in the middle of 

 its length; articulates by fibrous tissue anterodorsally 

 and anteroventrally with the quadrate; articulates by 

 slight interdigitation posterodorsally with the 

 metapterygoid, while along its posteroventral edge the 

 symplectic is attached to the fibrous tissue sheet that is 

 present between the preoperculum, hyomandlbular, and 

 metapterygoid. 



Palato-Pterygoid Region. 



Palatine. — T-shaped; articulates by fibrous tissue 

 ventrally with the ectopterygoid, anterodorsally with the 

 premaxillary and maxillary, and posterodorsally with the 

 laterally expanded anterior ends of the ethmoid and 



Ectopterygoid. —Elongate; articulates by slight 

 interdigitation anteroventrally with the quadrate, which 



it somewhat overlies, posteroventrally with the 

 metapterygoid, and posterodorsally with the mesoptery- 

 goid. Along the middle of its anterior edge it articulates 

 by tough fibrous tissue with the base of the palatine. 



Mesopterygoid. — Small; articulates by inter- 

 digitation anteriorly with the ectopterygoid and ven- 

 trally with the metapterygoid. 



Opercular Region. 



Operculiun. — Thin and flat, except dorsally where 

 it thickens into a rounded articular facet; articulates by 

 fibrous tissue with the slightly upraised area on the ven- 

 tral surface of the posterodorsal region of the hyoman- 

 dlbular, while ventrally it overlies and articulates by fi- 

 brous tissue with the suboperculum. 



Suboperculum. — Very thin and flat, slightly wider 

 anteriorly than posteriorly; held to the overlying oper- 

 culum by fibrous tissue. 



Interoperculum. — A straight rod, slightly wider 

 posteriorly than anteriorly; extends from the region of 

 the interhyal to about the anterior end of the preoper- 

 culum; articulates by a tough ligament anteriorly with 

 the angular in the lower jaw, while at its posterior end 

 two ligaments are present. One of these ligaments is 

 short and connects with the dorsal surface of the epi- 

 hyal, while the other one is long and runs posteriorly to 

 connect with the anterior edge of the operculum just 

 above the point where the operculum begins to overlie 

 the suboperculum. 



Preoperculum. — Not greatly expanded in its mid- 

 dle region; its dorsal surface only slightly flattened for ar- 

 ticulation with the quadrate; articulates by fibrous tis- 

 sue along the posterior portion of its dorsal edge with the 

 hyomandlbular, along the middle portion of its dorsal 

 edge with the symplectic, metapterygoid, and interhyal, 

 and along the anterior portion of its dorsal edge with the 

 quadrate. 



Upper Jaw. 



Premaxillary. — A slightly curved plate, wider dor- 

 sally than ventrally; its posterodorsal edge slightly con- 

 cave to articulate by fibrous tissue with the anterior ends 

 of the ethmoid and vomer. It also articulates by fibrous 

 tissue laterally with the medial surface of the palatine. 

 The anterior edge of the premaxillary forms the border of 

 the upper jaw, except for a short distance ventrally where 

 the maxillary does so. The premaxillary is in close ap- 

 position with the maxillary and articulates immovably 

 with it by fibrous tissue and slight interdigitation. The 

 flat dorsomedial edges of the two premaxillaries are held 

 closely to one another by fibrous tissue. Each premaxil- 

 lary bears seven teeth, four in an outer row and three in 

 an inner row. Both of these rows are in close contact with 



