794 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [48] 



region, there is a close agreement between them in the number and re- 

 lations of their ganoid plates."^" 



Of the Mandible. — A lateral figure of this very complex bone presents 

 us with a partial view of four of the elements that enter into its com- 

 position (Fig. 16). As usual, the chief part of the ramus is made up 

 by the dentary (Fig. 16 and PI. V, 17, I) or d). This bone expands 

 behind to articulate with the angular and surangular on lateral view, 

 while internally this expanded part is broadly concave, which concav- 

 ity is arched over by the splenial. Anteriorl3^ it meets the fellow of the 

 opposite side in a rather strong symphysis, the two bones developing 

 a single row of powerful teeth. These are of a conical form, curved 

 backwards, and very sharp at the apices. In Fig. 16 is shown where 

 two of these teeth have been shed, and the shallow pits they leave be- 

 hind them. The row of smaller teeth beyond, as shown in this figure, 

 belong to the splenial or the plates connecting it with the symphysis. 

 "Upon lateral view we may also see the angular and surangular to the 

 extent shown in Fig. 16, as well as the ossification marked z to be de- 

 scribed further on. 



The angular is the next in point of size to the dentary. Its outer 

 surface is convex and sculptured in the same manner as the ganoid 

 plates, while posteriorly it forms part of the articulation of the jaw. 



Above this element we find the surangular splint, which is carried up 

 to form the coronoid process, to be tipped with cartilage at its apex. 



Bridge, after his careful investigation of the mandible, says, in his pa- 

 per quoted above, that it "is an unusually complex structure, as each 

 ramus consists of not fewer than fourteen distinct elements. Meckel's 

 cartilage persists as a thin axial band of cartilage. Its distal end is os- 

 sified, and forms a small cylindrical mento-meckelian ossicle (Plate Y, 

 Fig. 17 of this paper, mt. mlc.), which lies in a groove on the inner side 

 of the symphysial end of the dentary (d). The proximal end of the car- 

 tilage is the seat of at least four distinct ossific centers. Of these, three 

 are arranged in a linear series proceeding from the angular extremity of 

 the mandible. These are referred to in the annexed plates [figures] as 

 «, &, and c. Of these the ossicles «. and h form the anterior and poste- 

 rior boundaries of the articular cup for the quadrate, and are separated 

 from each other by that portion of Meckel's cartilage which forms the 

 bottom of the cup. The bone marked c is much smaller than the other 

 two. That part of Meckel's cartilage adjacent to the articular cup is 

 produced vertically upwards and forwards into a well-marked ' coro- 

 noid process' (cr). The base of this process is the seat of an ossifica- 

 tion (b) which forms the outer side of the articular cup, and fits into 

 the cup-shaped distal end of the preoperculum. Thus these three bones, 

 a, &, and c, contribute to the formation of the concave articular surface 

 for the quadrate." 



'^IMd., page 609. 



