DEALFISII. 
317 
wards, thin, small, with few rays and rounded at the 
tip, the first ray being extremely short, the second the 
thickest and the fifth the longest". The head is com- 
paratively small, its length being always less than the 
greatest depth of the body''; but the eyes are large 1 ', flat- 
tened to the plane of the cheeks, and set about half-way 
up the body, the distance between them and the frontal 
profile being equal to their radius. The pupil is oblong 
and set obliquely downwards in a backward direction. 
When the mouth is closed, the head, when seen 
from the side, is of a quadrilateral shape. The straight 
profile of the forehead and snout slopes downwards al- 
most. at a right angle to the ascending under surface 
of the lower jaw, the point of which projects, however, 
beyond the upper jaw. The corners of the mouth are 
now entirely hidden at the sides, being covered by the | 
intermaxillary and the maxillary bones; but the upper 
margins of the lower jaw rise vertically within the gape. 
The hind corner of the head, formed by the suboper- 
culum, is somewhat rounded and elongated. The lower 
corner of the square is formed by the angular part of 
the lower jaw, which is produced behind into a blunt 
spine d . The cheek is naked; only in front of the eye 
do we find two suborbital or preorbital bones, the lower 
being so narrow that it only just separates the eye 
from the point of the high, triangular branch of the 
lower jaw, which, in its turn, is covered by the broad, 
thin maxillary bone*. The latter, like all the opercular 
bones, is of a thin, spongeous texture, externally ca- 
vernous, with radiating elevated ridges. It. is obliquely 
linguiform, the breadth being rather more than half 
the length. The preoperculum is crescent-shaped, the 
operculum almost like the upper half of the preoper- 
culum in shape, the part of the suboperculum which 
is externally visible, narrow, and the interoperculum, 
which forms the greater part of the lower margin of 
the gill-cover, of fairly uniform breadth. All these 
bones are membranous at the margin. The gill-open- 
ings are large, their height' being about equal to the 
total length of the interoperculum and suboperculum. 
The branchiostegal membrane is united to the narrow 
isthmus back to a point vertically below the hind mar- 
gin of the eye ; but in front of this point it hangs in 
a fold across the isthmus, thus appearing double, when 
the jaws are drawn back. At these times too, it is co- 
vered, together with the whole of the branchial appa- 
ratus and the isthmus, by the interopercula and the 
branches of the lower jaw. 
But the appearance of the head is quite different 
when the mouth is protruded. The nasal processes® 1 of 
the intermaxillary bones extend right up to the occi- 
put, where they may slide to and fro in the deep groove 
in the frontal bones. When they are protruded, they 
draw with them the maxillary bones, which are only 
loosely connected with the palate, and are thus capable 
of extensive protrusion. The snout now attains a length 
which may even exceed that of the rest of the head, 
and acquires an appearance, when seen from the side, 
not unlike that of a swine’s snout. Now, when the 
branchial apparatus is expanded, the hyoid bone, to- 
gether with the broad ceratohyoid bones, projects down 
below the isthmus, and the branchiostegal membrane 
emerges from the opercular apparatus. 
The nostrils are comparatively small, the posterior 
being long, but narrow, and situated in the form of a 
perpendicular slit close to the anterior upper margin 
of the orbit. The anterior nostril is separated from it 
by a dermal bridge. 
“ The pectoral fins are perfect in a specimen caught in 1879, on the lee of Vinga (Gothenburg). Their length is nearly 4 % of that 
of the body or 1 /. of the greatest depth of the latter. 
b In the specimen from Vinga (925 mm. long) the length of the head, measured from the middle of the margin of the upper jaw 
(the tip of the snout), when drawn back, is 11 3 % of that of the body. This coincides with Let ken’s measurement of a Trachypterus 
arcticus 830 mm. long, and also with Emery’s measurements of the largest specimens of Track, iris in his possession (1,120 — 1,410 mm. 
long). According to Lijtken, however, in specimens of Track, arcticus about 1 in. in length, the average length of the head is 14'2 % 
thereof, in specimens about 13 din. long, 12’4 %, and in specimens about 2 m. long, ll'l /. 
c In specimens about 1 m. long the longitudinal diameter of the orbit is about 30 % of the length of the head. In specimens 1 '/V, 
m. in length it may sink to 25‘8 / of the length of the head, according to Lutken. In many cases, however, the eye on the one side of 
the head is at least somewhat larger than that on the other. 
d In the specimen from Vinga the length of the right branch of the lower jaw is 57 % of that of the head, of the left only 52 1 / 2 /. 
Though the snout has been damaged, this does not seem enough entirely to explain the difference. In the other two specimens preserved in 
spirits in the Royal Museum, however, there is no such difference: but the gape is crooked when the mouth is protruded. 
e In the specimen from Vinga the length of the right maxillary bone is 40 % of that of the head, of the left only 34’3 %. Cf. 
the preceding note. 
f In the specimen from Vinga the height of the gill-openings is 2 /s of H ie length of the head. 
v In the specimen from Vinga the length of the nasal processes, together with the anterior height of the body of the intermaxillary 
bones, is 75 mm. or very nearly 3 / 4 of the length of the head. 
