CARP. 
in front towards the snout. This depression is most 
distinct in old specimens, in which the externally bare 
hind parts of the frontal bones too are more distinctly 
marked with radiating striae. The eyes are round (with 
the longitudinal diameter slightly greater than the ver- 
tical) and are set rather high, by far the greater part 
of them lying above a horizontal line from the tip of 
the snout to the middle of the caudal fin. In speci- 
mens between 3 and 5 dm. long their longitudinal dia- 
meter measures about 15 — 14 % of the length of the 
head; in younger Carp they are as usual comparatively 
larger, their longitudinal diameter, when the body is 
2 dm. long, being about 1 / 5 of the length of the head, 
when the body is 3 / 4 dm. long, about 1 / i of the same. 
The nasal cavities lie just, in front of the upper an- 
terior corners of the orbits. The two nostrils on each 
side are fairly large and round, the diameter of the 
posterior being about equal to its distance from the 
orbit. They are set close to each other, the anterior 
obliquely on the inner side of the posterior; and the 
margin of the anterior nostril is raised behind in an 
obliquely cut, canaliculate form, so as to compose a 
lid with which the aperture may be closed. The distance 
between the two anterior nostrils is somewhat less than 
their distance from the middle of the tip of the snout, 
but about equal to half the breadth of the interorbital 
space above the centre of the eyes. The length of the 
snout varies, however, quite considerably, from 1 / 3 of 
the length of the head in young Carp to about 3D % 
thereof in old. The mouth is fully terminal, the cleft, 
when the mouth is closed, slightly ascending, and the 
gape, when protruded and wide open, of a rounded 
quadrangular form. The lips are fleshy; the upper lip 
is double, the maxillary bone being also furnished with 
a dermal fold, in which the two pairs of barbels have 
their origin; the lower lip hangs down along the sides 
of the lower jaw in front of the corners of the mouth. 
The barbels are flattened at the base and vary con- 
siderably in length; the lower (at the corners of the 
mouth) may be half as long again, according to Fatio, 
as the diameter of the eye, but are usually shorter and 
in young Carp much shorter than the diameter of the 
eye; the upper (anterior), which are set about half way 
along the maxillary bones or a little higher, are only 
half or one-third as long as the lower; but we must 
not forget that during life these barbels are capable of 
extension and contraction. The length of the upper 
jaw, measured from the middle of the tip of the snout 
725 
to the hind extremity of the maxillary bones, is in 
adult Carp about 27 or 28 %, and the length of the 
lower jaw 31 — 36 % of the length of the head. The 
gill-openings extend from the upper posterior corner 
of the operculum to the isthmus, about to the perpen- 
dicular from the articular knob (upper anterior corner) 
of the operculum. The branchiostegal membranes are 
below united to the isthmus at a distance from each 
other which in old specimens is equal to the longi- 
tudinal diameter of the eyes. The branchiostegal rays 
are 3 in number, in accordance with the general rule 
within the family; but Fatio on one occasion found 4 
rays in each membrane. The operculum is obliquely 
quadrangular (rhomboidal), with the lower posterior 
angle rounded and obtuse. The anterior margin is the 
longest, being about equal in length to the postorbital 
part of the head, or to about half the entire length of 
the head. The lower margin is slightly indented in a very 
elongated S-shape or even straight. The surface of the 
operculum is striated by granulated ridges with inter- 
jacent. grooves, radiating backwards and downwards from 
the articular knob. The crescent-shaped suboperculum, 
which coasts the inferior margin of the operculum, is 
distinctly (about 1 / 3 ) longer than the lower jaw. The 
triangular interoperculum, pointed at the top, tills the 
angle between the two bones just mentioned and the 
lower part of the preoperculum, and coasts the inside 
of the horizontal (lower) arm of this last bone forward 
to the point of union with the articulation of the lower 
jaw. The hind angle of the preoperculum is obtuse 
and rounded. The cheeks are soft; but the space be- 
tween the eye and the uppermost part of the preoper- 
culum is filled by the posterior bones of the orbital 
ring. The suborbital bones are also thick and firm, 
striated like the operculum. The gill-rakers are short 
and rather scattered (18 — 20 in the outer row on the 
first branchial arch), consisting of pointed triangular 
disks with dermal papillte on the inner margin. The 
lower pharyngeals (fig. 178), the mucous membrane of 
which is fringed at the outer superior margin with 
similar, but. smaller gill-rakers, 22 in number, are fur- 
nished within this margin as a rule with five teeth each; 
but while the teeth a, re being shed, one or two of these 
may be wanting or may lie hidden or loose in the 
mucous membrane. The largest teeth are 3 in number, 
set in an inner row. The first of them is bluntly conical, 
with a greater or less degree of lateral compression, 
and never shows signs of wear by grinding, but bears at 
