1082 
SCANDINAVIAN FISHES. 
suborbital (preorbital) margin of the Teleosts; but it can- 
not be fully homologous therewith, for here the nostrils 
are situated below it. The nostrils, which lie just in front 
of the median upper lip, are externally — each being- 
bounded laterally by the lateral upper lip of that side — 
simple, round, and rather large apertures, separated by 
a thin septum. On raising the lateral upper lip we find, 
however, that each nasal cavity besides possesses a pos- 
terior opening, a dermal fold, bent into several curves 
and internally supported by a cartilaginous disk (fig. 
294, ln 2 ), being turned inwards from the outer margin 
of the nasal cavity and forming the greater part of the 
posterior limit of the anterior nostril. To meet the inner 
edge of this dermal fold — though without being con- 
tiguous with it — a longer fold rises from the inner 
margin of the nasal cavity, a true narial passage being 
thus present, though not fully closed behind 3 . Exter- 
nally the nasal cavity is covered by the lateral upper 
lip, so that the posterior nostril opens within the lip, 
Fig. 304. Jaw-teeth of the left side in the Northern Chimarra ( Cliimcera 
monstrosa). After Agassiz. A, seen from without; B , from within. 
da , anterior dental plate of the upper jaw; dp , posterior dental plate of 
the same; di, dental plate of the lower jaw. Cf. fig. 294 (p. 1065). 
inside the cavity of the mouth. The Chimaera can 
thus respire even when the mouth is closed. 
The lips are thick and fleshy, studded outside and 
at the margins with small protuberances (papillae), the 
upper lip, as we have already hinted, being divided 
into three parts, a quadrangular middle part (median 
upper lip) and two larger wing-shaped lateral lobes (la- 
teral upper lips). The median upper lip as well as the 
underlip is double. The former partially covers the two 
anterior dental plates (fig. 294, da) of the upper jaw. 
The underlip is entire in front, but furnished behind 
with a broad, pendent flap at each corner of the mouth. 
The dentition of the mouth consists of two pairs of 
palato-dental plates, one pair (figs. 294 and 304, da) 
before the other (dp), at the margins of the upper jaw, 
and a single pair of mandibular plates (di). The inter- 
maxillary (prepalatine) plates (da) are quadrangular and 
most distinctly grooved, with 6 rounded ridges; the lateral 
maxillary (palatine) plates (dp) and the mandibular plates 
(di) are more triangular, undulate and nodose on the 
inside. The tongue is small, but free at the tip, and is 
densely set with papillae. The front of the branchial arches 
is also studded with similar papillae; but soft gill-rakers, 
about 12 on the first branchial arch, are besides present. 
The three free gill-arches are complete (with bran- 
chial lamella; on both sides), but both before and behind 
them lies a half gill (single row of lamellae), the former 
coalescent with the operculum, the latter with the hind 
(abdominal) wall of the branchial cavity. The gill- 
openings are about equal in depth to the length of 
the orbits, and are set far down, though separated by 
an isthmus the breadth of which is about equal to the 
depth of the orbits. 
The general form of the fins we have already no- 
ticed. The triangular first dorsal begins just behind the 
head, the length of which varies between 80 and 90 % 
of the distance from this fin to the tip of the snout. 
The spine at its anterior margin lies exactly above the 
base of the pectoral fin and sometimes (in the males) is 
only a little shorter than the head; sometimes (usually 
in the females) only 4 / 5 as long. It is rather sharp in 
front and is marked anteriorly on each side with a 
distinct groove. Both its posterior margins are armed 
superiorly, usually somewhat more than half-way clown 
the spine, with pointed, descending prickles, and its top 
is usually free from the remainder of the fin to a point 
a little further downwards. Behind the spine the fin is 
supported by fibrils, gathered into about a dozen sepa- 
rate bundles, which resemble fin-rays. The posterior 
margin is somewhat concave, and the tin-membrane is 
prolongated to the vanishing point backwards along the 
dorsal margin and more or less near to the second 
dorsal fin. The latter tin begins at a distance from the 
tip of the snout measuring a little more or less than 
twice the length of the head and extends back about 
half-way along the rest of the body, measured from the 
commencement of the fin. Its height is almost uniform 
and only about 1 / i or 1 / 5 of that of the first dorsal. 
Just behind its termination the upper caudal lobe begins. 
The lanceolate caudal' fin is made up of two almost si- 
milar lobes, one over and one under the tail, whose tip 
narrows uniformly to a filament, and of which they 
occupy the anterior half or third, before they gradually 
and, at last, imperceptibly disappear. The anal fin con- 
a Answering to one of the stages in the development of the nostrils of the higher vertebrates. 
