OF THE SKULL IK LEPIDOSTEUS OSSEUS. 
479 
in the post-orbital region, but it then widens to thrice its breadth even in the ethmoidal 
region. It flanks the basipterygoids (b.pg.) with a pair of small wings, is spread out 
under the auditory capsules (cut.), and applies itself as a forked splint to the under face 
of the basioccipital ( b.o.). Behind, for three-fifths of their length, the palatine splints 
(pa'.) are bound on their inner edge by a larger, but similar bone; this is the ptery¬ 
goid (fig. 3, pg.) ; both these bones are seen in their relation to the suspensorium in 
other figures (Plate 37, fig. 4, and Plate 38, fig. 5, pa'., pg.). The pterygoids acquire 
a fine bony rasp when they lie close to the palatal surface. Each bone is a long style 
in front, and then widens gradually so as to become a broad spatula in the orbital 
region. 
The styloid palato-pterygoid cartilage is applied to its outer face above, but the bone 
passes backwards, and invests three-fourths of the inner face of the broad suspensorium 
(see Plate 38, pg.), ending behind, with a thin, rounded margin. 
When these parts are removed from the rest of the skull (Plate 37, fig. 4, and Plate 
38, fig. 5) their parosteal relation to the prognathous suspensorium is clearly seen. 
Over the edge of the suspensorium, in its broadest part, there is a third parostosis; 
this is the mesopterygoid (Plate 37, fig. 4, and Plate 38, fig. 5, ms.pg.). It is a thin, 
falcate bone above, one-sixth the length, and one-sixth the width, of the pterygoid. 
A fourth splint is applied to the suspensorium, and this, like the last, is extremely 
small as compared with what is seen in the Teleostei; this is the preoperculum 
(p.op.) ; this bone is falcate, narrow, gently curved downwards, pointed behind, where 
it lies on the interopercular, and roughly notched in front, where it binds on the 
outside of the quadrate bone (q.) ; it is only one-third the length and one-third the 
width of the succeeding bone—the interopercular (i.op .); whereas in the Teleostei 
it is much the larger bone, as a rule. 
The free part of the lower jaw, or mandible, is of great length, and the dentary 
bone covers it from end to end (Plate 37, fig. 4, d .); on the inside (Plate 38, fig. 5, d.) 
it is only seen at the edges of the jaw. Under its upper edge, on the inside, a much 
smaller bone, three-fourths its length, binds on the upper edge of the cartilaginous 
axis (mlc.) ; this is the splenial (spl.). 
Behind the splenial, on the inner side (Plate 38, fig. 5 cr.) the coronoid is seen as a 
pedate tract of bone with its heel behind ; it binds on the inside of the fore part of the 
large cartilaginous coronoid (cr.c.). Under the short angular process of the articular 
cartilage there is a small angulare (ag.), and outside the large, ear-shaped coronoid 
cartilage, on its convex face, there is a considerable scale of an oval shape, and placed 
obliquely forwards and upwards ; this is the supra-angulare (Plate 37, fig. 4, s.ag.). 
The specialised “ scutes ” just desuribed belong to the mandibular arch ; those next 
to be noticed belong to the hyoid. On the knob of the hyomandibular a large oval 
scute is articulated by its capped fore end: this is the operculare (Plate 37, fig. 1, op.); 
below this a similar bone is seen, but of an uncinate or semi-crescentic form, with 
its sharp end behind, and its upper edge inside the operculare; this is the sub- 
operculare (s.op.). 
MDCCCLXXXIT. 3 Q 
