342 PROF. T. W. BRIDGE ON THE MORPHOLOGY OF THE SKULL 



Wiedersheim (I. c), and each ramus consists of articular, coronoid, and dentigerous 

 regions, and a persistent and curiously-modified Meckelian cartilage (PI. XXVIII. 

 figs. 7 and 8, and PI. XXIX. fig. 9). 



Meckel's cartilage consists of a thick proximal portion (fig. 8, mk.c), deeply 

 excavated posteriorly so as to form a concave, transversely-disposed, articular surface 

 for the suspensorium, and of a thin band-like extension of the foregoing, which makes 

 its appearance on the outer surface of the ramus in front of the angular bone (fig. 7), 

 and thence runs forvrard- in a groove near the lov^er border of the splenial (sp.) as far 

 as the mandibular symphysis, where it becames continuous with its fellow of the 

 opposite side in an expanded symphysial plate (fig. 9). In the angle between the 

 anterior and central of the three cutting tooth-plates with which each mandibular 

 ramus is furnished, the Meckelian cartilage gives off a vertically-disposed ascending 

 process (fig. 7). Three similar, but shorter, processes are also given oft' from the upper 

 margin of the symphysial plate, of which two are supero-lateral and one central, and 

 lie in the angle which the anterior tooth-plate forms with its fellow of the opposite 

 ramus (fig. 9). A short cartilaginous nodule may also be found between the central 

 and posterior tooth-plates, but is connected with the Meckelian cartilage only by 

 fibrous tissue (fig. 7). Morphologically, it is possible that the symphysial plate and 

 its supero-lateral processes may represent lower labials, as Rose {I. c.) has suggested in 

 the case of Protopferus ; but at present no valid reason has been assigned for 

 regarding them as other than expansions or outgrowths from the Meckelian cartilage 

 for -the support of certain folds of mucous membrane which occupy the outer angles of 

 the tooth-plates, and, as Rose {I. c.) himself as shown, are important factors in the 

 process of tooth-regeneration and growth. 



Two bones only are i-epresented in each half of the mandible. Of these, the splenial 

 (in Protopterus, the " dentary " of Owen, Peters, and Miall, and the " articulare " of 

 Wiedersheim ; in Ceratodus, the " dentary " of Giinther, and the " splenial " of Huxley) 

 is by far the larger, and forms nearly the whole of the bony portion of each ramus, 

 retaining, however, its primai-y and normal position in relation with the inner surface 

 of Meckel's cartilage (figs. 7-9, s/j.). Posteriorly and dorsally it rises into an unusually 

 strong coronoid process (cor.p.) for the insertion of the powerful temporal and 

 masseter muscles, and anteriorly articulates and partially fuses with its fellow in an 

 exceptionally massive symphysis (fig. 8, im.sy.), which, internally as well as externally, 

 is produced into a strong " spina mentalis " (fig. 8, s.m.i. ; fig. 9, s.m.e.). For the 

 anterior half of its extent the bone supports dorsally the three splenial or mandibular 

 tooth-plates (fig. 7, a.m.t., m.m.f., p.m.t.). The second bone is the "angular" (in 

 Protopterus the "articular" of Owen, the "dentale externum" of Wiedersheim, and 

 the " angular " of Peters and Miall ; in Ceratodus, the " articulary " of Giinther, and the 

 " angular " of Huxley). It is a relatively small bone (figs. 7, 9, an.), commencing at 

 the extreme angle of the jaw and thence extending for a short distance forward, external 



