FLYING-FISH. 
359 
waves, this is probably nothing more than the effect 
of the current of air that rises from the surface, and 
is formed in the trough of the waves (fig. 95) just as 
a stream eddies when it passes a promontory, or from 
the same cause as that from which the flame of a candle 
is attracted towards a surface, if we blow straight to- 
wards that surface through a tube, the end of which 
is beside, but behind the candle. 
In order to facilitate its flight the Flying-fish has 
several peculiarities of structure. Thus we first observe 
the advanced development of the pectoral fins and the 
shape of their rays. The first ray, which has to divide 
the air, is sharply compressed in the plane of the fin as 
in the two preceding genera; but the rest of the rays are 
compressed in the opposite direction or rather strength- 
ened in their proximal part (the part nearest the inser- 
tion) by a downward (when the fins are at rest, outer) 
edge along the anterior (when the fins are at rest, 
superior) margin, the section of these rays in the pro- 
Fig. 95. Tlie lifting of the Flying-fish by the wind, the direction 
of which is shown by the arrows. After Mobius. 
ximal (inner) part of the fins thus forming an angle 
opening backwards (when the fins are at rest, downwards). 
The fin-membrane is attached to the posterior (when 
the fins are expanded, upper) margin of the rays; and 
the base of the pectoral fins, which, when the fins are 
at rest, runs upwards in front and downwards behind, 
assumes an almost horizontal direction when the fins are 
expanded, as the anterior (upper) rays are drawn down- 
wards at the base, the fish thus resting on that side of 
the fins which was formerly the exterior. On the un- 
der surface of the expanded fins a deep groove, opening 
posteriorly and inferiorly, is thus formed between each 
pair of rays; and it is in these grooves that the up- 
ward current of air we have just mentioned, plays its 
part in lifting the fish. 
The muscles of the pectoral fins serve chiefly to 
expand them. They also assist to retain them in the 
expanded position; but this object is also promoted by 
the current of air itself, and the rays are kept in po- 
sition not only by the fin-membrane but also by special 
ligaments, which cross from one ray to another in the 
proximal part of the fin. Thus any extraordinary 
strength — such as would be necessary if the flight 
were a true one, accompanied by the flapping of the 
wings — is scarcely needed, and the muscles of the 
pectoral fins are hardly any thicker than in the gener- 
ality of Teleosts. These muscles are also arranged in 
the usual way, in two layers, a superficial and a deeper, 
on each side of the shoulder-blades and coracoid bones. 
The common extensory muscle of the two first (upper- 
most) rays, however, has a long surface of origin at 
the bottom of the clavicular groove, and has its sinew 
inserted under a transverse band like a roller, which 
joins the shoulder-blade to the clavicular bone. Still, 
the lack of any extraordinary degree of thickness in 
these muscles is compensated, as in the two preceding 
genera, by their extension. Their surface of origin, 
the shoulder-girdle proper — the clavicular bone, the 
shoulder-blade and the coracoid bone, especially the 
last of these three — is also extraordinarily large here 
as in Ramphistoma. 
The strength required to produce the great speed 
is given by the large lateral muscles of the body; and 
their surfaces of origin in front — the occiput and the 
anterior vertebra; — are of the type we have attributed 
above to all the Synentognates. Their points of insertion 
on the last caudal vertebrae are also strengthened. Here, 
as in the Garpike — and we have observed similar for- 
mations in the majority of the Mackerels — we find on 
each side of the last caudal vertebra a strong, project- 
ing, osseous knob; and in the Flying-fish the upper 
spinous processes of the last six or seven caudal verte- 
brae are also longitudinally extended and contiguous. 
In the Great Flying-fish and its kindred species 
the ventral fins also help to increase the width of the 
fish, and thus also increase the size of the column of 
air that supports it. Their first ray is compressed and 
sharp, but repeatedly branched. The second ray re- 
sembles the first, but is considerably longer; and the 
third ray is the longest of all. 
As a counterpoise to the weight of the great mass 
of muscles the Flying-fish is furnished with an extra- 
ordinarily large air-bladder, which occupies the greater 
portion of the abdominal cavity (fig. 96), and is con- 
tinued behind within the closed haemal arches of the 
caudal vertebrae. In the air-bladder of the Flying-fish 
Humboldt found a strikingly small quantity of oxygen", 
0'04 oxygen, 0'94 nitrogen and 0’02 carbonic acid gas; see Reise AHqu. Geg ., I, p. 309. 
