SHEATFISH. 
695 
breadth of the interorbital space, and also only a little 
more than 14 % of the length of the snout. As appears 
from these measurements, the breadth of the low, but 
rounded interorbital space measures about l / 2 (varying, 
however, between 55 and 48 %) of the length of the 
head, and the length of the snout usually a little more 
than V 3 (varying between 38 and 33 %) of the same 
length. Here, however, as usual, the length of the snout 
is measured obliquely (from the anterior margin of the 
eyes to the middle of the tip of the snout): its real 
length (the distance between its tip and the middle of 
the line joining the anterior margins of the eyes) is 
in young specimens rather more than 1 J 2 , in specimens 
1 in. long rather less than 1 / s , and in our largest spe- 
cimen about a / 5 of the breadth of the interorbital space. 
In proportion to the entire length of the head the real 
leno’th of the snout decreases, during the growth of the 
fish from a size of 3 dm. to one of 2 in., from 1 / 4 to 
only J / 5 of the said length of the head, and at the same 
time from about 41 to 28 % of the postorbital length 
of the head. The eyes thus lie invariably in the fore- 
most third of the head, just behind the line between the 
hind margins of the corners of the mouth. Just in front 
of this line, or exactly in it, lie the posterior pair of 
nostrils. These nostrils are small and round, and are 
situated so far inwards that the distance between them, 
which is relatively less in old specimens, measures only 
about 66 — 56 % of the breadth of the interorbital space. 
The anterior pair of nostrils lie far out on the snout, 
in the line between the maxillary barbels, and at a 
somewhat -smaller distance from each other. The margin 
of all the nostrils is tubular, the posterior pair being 
more elevated in a funnel-shape. 
Of each of the maxillary bones there remains, as 
Ave have indicated above, hardly more than the articular 
knob itself, a small, triangular or scaphoid bone, holloAv 
on the outside and articulating on the inside, which is 
button-shaped, with the lateral ethmoid (prefrontal) bone 
and the intermaxillary bone. But on the lower anterior 
side of this bone Ave find another, still smaller, supple- 
mentary bone, forming the base of the maxillary barbel, 
Avhich is long and narroAV, but compressed, and may be 
moA r ecl in all directions. The length of this barbel is, 
hoAvever, extremely variable. Noav and then the barbel 
on one side of the body differs from that on the other. 
As a rule too, these barbels are comparatively shorter 
in old specimens than in young: in a specimen 1 metre 
long the longest barbel measured someAvhat more than 
7i 0 °f the length of the body, in a specimen 2 metres 
long not quite l / 6 of the same length or, in other Avords, 
a little more than the length of the head. The tAvo 
pairs of barbels on the loAver jaw are considerably shorter, 
the anterior pair being also shorter than the posterior, 
which generally extend to about a line Avith the hind 
margin of the preoperculum or with the articulation of 
the operculum. These barbels are not set on the loAver 
jaAv itself, but a little farther inwards, on the skin be- 
tAveen the branches of the jaw, the anterior pair nearly 
beloAv the anterior nostrils, the posterior pair beloAv 
the anterior margins of the eyes. 
The surface of the head is smooth, and the bones 
and cavities Avhich othenvise give many Glanomorphs 
one or more important characters, are perceptible only 
to the touch. Within this series of families Ave rather 
constantly find, in the forms that have a more or less 
fully armoured head, a longitudinal groove, or an oblong, 
naked patch, along the middle of the forehead and snout. 
Here, as in the other forms the head of which is des- 
titute of dermal ossifications, no groove of this kind is 
externally perceptible; but in the skull Ave find a long 
opening (fontanel) between the anterior parts of the 
frontal bones proper, and this opening is continued 
betAreen the posterior parts of the ethmoid bone. 
In the same Avay Ave find no external trace of the 
suborbital ring; but in the skeleton it displays some 
striking peculiarities. The foremost bone in this ring 
(the preorbital bone) is comparatively small, flat, tri- 
angular, and acute-angled in front. One side of this 
bone lies on the outer top of the lateral ethmoid bone, 
and the point in front is united by ligaments to the 
top of the long lateral process of the ethmoid bone 
proper. With its inside this bone forms the outer mar- 
gin of the nasal cavity, the inner margin of Avhich is 
formed by the long, but also fairly broad nasal bone Avith 
its someAvhat crescent-like shape. Both the nasal bone 
and the preorbital bone are furnished on their upper 
surface Avith hollows and grooves for the ramifications 
(muciferous ducts) of the lateral line. The second sub- 
orbital bone forms the anterior margin of the orbit and 
occupies a singular position, straight outwards and down- 
Avards from the lateral ethmoid bone, Avhile its length 
is so great that the tip lies above the loAver jaw, though 
Avithout coalescing Avith the latter, just in front of the 
articulation thereof. At the distal part of this sub- 
orbital bone, Avith its anterior side united to the pos- 
terior side thereof, lies the third suborbital bone, Avhich 
Scandinavian Fishes. 
88 
