696 
SCANDINAVIAN FISHES. 
is angular, and forms with the shorter (inner) arm a 
part of the outer margin of the orbit. These two sub- 
orbital bones thus form with their outer parts an osseous 
ridge projecting from the orbital ring, a structure re- 
minding us of that which in the Cottoids and the Lump 
Suckers unites the orbital ring to the preoperculum. 
The fourth • suborbital bone, which is the longest, is 
curved in an S-shape. With its lower curve it forms 
a part of the lower (outer) and the whole of the pos- 
terior margin of the orbit. With its upper curve it 
bends backwards to be united by ligaments to the out- 
side of the anterior extremity of the posterior frontal 
bone, which at this point, outside the frontal bone pro- 
per, meets the hind extremity of the lateral ethmoid 
(prefrontal) bone. 
The crescent-shaped, obliquely set preopercula are 
also externally indistinct, being entirely covered by the 
skin; but a distinct dermal fold on each side marks the 
position of the margins of the operculum and interoper- 
culum. The former is triangular, with the upper margin 
convex and the lower posterior margin slightly concave. 
The interoperculum too, which also replaces the suboper- 
culum, is triangular in form, but forked behind, with 
the upper posterior corner projecting obliquely under the 
operculum. The anterior extremity of the interoper- 
culum is united by a long and strong ligament to the 
hind extremity (angular part) of the lower jaw; but this 
ligament runs along the inside of the interoperculum as 
Avell, and is attached here and also, no less firmly, to 
the outside of the upper part of the epihyoid bone®. 
Behind the said dermal fold marking the hind mar- 
gin of the opercular apparatus proper, the head is con- 
tinued on each side by a broad branch iostegal membrane, 
which lies in a rather indistinct flap above the upper 
angle of the base of the pectoral fin. Both of the 
branchiostegal membranes are entirely free from the 
isthmus and united to each other only at the extreme 
front for a very short distance, nearly below the corners 
of the mouth; but the left branchiostegal membrane 
overlaps the right under the isthmus to a considerable 
extent. The branchiostegal rays are numerous; 13 or 
14 of them are set on the ceratohyoid bone and are 
fairly uniform in thickness and terete, but narrow and 
pointed. The last two of these rays are set on the epi- 
hyoid bone, and the last in particular is flat towards 
the tip, externally grooved (hollowed in a longitudinal 
direction), and fairly broad. 
The cards of teeth in the lower jaw, on the inter- 
maxillary bones, and on the head of the vomer are of 
similar form and parallel, curved like a crescent and of 
fairly uniform breadth, but growing narrower as usual 
behind (distally on the vomer). They are composed of 
dense, pointed, and somewhat recurved teeth of uniform 
size, which are comparatively small, but in so large a 
fish still form a powerful weapon. In the lower jaw 
and on the intermaxillary bones the halves of the cards 
are separate in front; but the vomerine card of teeth 
presents an unbroken surface 6 . Of the three upper pha- 
ryngeals on each side only the hindmost is furnished 
with teeth, and this bone is also the only one of the 
three that is visible in the pharynx, having extended 
under the other two, which are small and serve to sup- 
port it and to attach it to the under surface of the skull. 
The patch of teeth on the first-mentioned pharyngeal is 
fairly large, convex and elliptical. Each of the two 
lower pharyngeals is furnished with an oblong patch of 
teeth, broader in front, narrower behind (above), and 
concave on the insideb All the pharyngeal teeth are 
pointed and resemble the jaw-teeth, but are smaller, 
smallest on the lower pharyngeals and in the outer pos- 
terior corner of the upper cards. The gill-rakers are 
scattered and fairly short, but pointed like teeth. On 
the first and second branchial arches they are set in a 
single row, and on the front of the first arch we find 
9 or 10 on the ceratobranchial bone and 2 on the lower 
part of the epibranchial bone. In some cases the lower 
pharyngeals are also furnished on their outer margin 
with a row of short, similar spines. The palatal folds 
within the cards of jaw-teeth are well-developed, but 
the upper is quite shallow. The upper jaw is not ca- 
pable of the slightest protrusion, for the intermaxillary 
bones are firmly united by ligaments not only to the 
large anterior process of the ethmoid bone proper, but 
also, though at a somewhat greater distance, to the 
a Cf. above, p. 664, note A, on the singular position of the interoperculum in the Syngnathince. 
5 In a Sheatfish 2 metres long the patch of teeth on each half of the lower jaw is 29 mm. broad in front and 118 mm. long, though 
the posterior (outer) part for a distance of 40 mm. is considerably narrower than the anterior part; the patch on each intermaxillary bone is 
85 mm. long and 22 mm. broad, a breadth also attained by the vomerine card of teeth, which measured across the palate is 96 mm. in length. 
c In a Sheatfish 2 metres long each of the cards of teeth on the upper pharyngeals is 47 mm. long and 30 mm. broad, on the lower 
pharyngeals 85 mm. long and 24 mm. broad at the broadest point. In a Sheatfish 1 metre long each of the two cards of teeth on the upper 
pharyngeals is 30 mm. long and 21 mm. broad, on the lower pharyngeals 47 mm. long and 14 mm. broad at the broadest point. 
