CEANIAL OSTEOLOGY OF THE OSTEOQLOSSIDiE. 267 



Las'tlie form of a thin yertical plate with concave upper border ; 

 it is constituted mainly by the dentary, but the ectosteal articular 

 forms the posterior extremity. The endosteal articular and the 

 ectosteal articular are distinct and separate readily. The 

 articular surface for the quadrate is formed mainly by the end- 

 osteal articular, but partly also by the angular, which is a 

 separate bone. There is no sesamoid articular. The ventro- 

 lateral surfaces of the angular, ectosteal articular, and dentary are 

 sculptured. 



The dentary bears a single row of about 30 teeth similar in 

 form and size to those of the maxilla. The bone is very complete 

 on the inner or lingual side of Meckel's cartilage, and bears one, 

 two, or three elliptical patches of small teeth in the position shown 

 in fig. 16 at s. These teeth were noticed by Valenciennes, who 

 wrote concerning them: — " Au c6t6 interne de chaque branche 

 ■de la mandibule je vols, sur une assez large plaque triangulaire, 

 un groupe de fines scabrosites ou de petites dents, semblables 

 a celles des palatins " (Hist. Nat. Poiss. xix. 1846, p. 446). 

 Although the bony lamina that bears the teeth occupies the 

 position of the splenial bone, it is not a distinct plate of bone as 

 might be concluded from the remark of Owen (Anat. of Veft. 

 i. p. 123) — " The Sudis, fig. 88 *, the Polypterus, and Amia, have 

 the splint-like plate along the inner surface of the ramus, called 

 ' splenial ' ; it supports teeth and developes a coronoid process." 

 The passage continues : — "In both Sudis and Lepidosteus there is 

 superadded a small bony piece, ih. 29 a, answering to the sur- 

 angular in Eeptiles." This bone, marked 29 «, is, I believe, 

 merely the endosteal articular displaced. 



Syopalatine Series (fig. 16). — The head by which the hyo- 

 mandibular articulates with the cranium is indistinctly divided 

 into a small front head and a large hinder one, broad antero- 

 posteriorly. The head that articulates with the opercular bone is 

 long drawn out, and on the external face of the hyomandibular 

 there is a short projection that engages with the anterior edge 

 of the upper part of the preopercular. The axis of the hyomandi- 

 bular slopes more forward than downward. The metapterygoid 

 is of average size, but only a small portion of it is visible in the 

 buccal aspect of the hyopaiatine ai'ch. The symplectic is large 

 and of curious shape, since it throws out jagged-edged laminae 



* Fig. 88 represents the disarticulated mandible of Ampaima gigas. 



