i 5 O r THE H E A R T , V E S S E L S,
The blood iffues from both ends of all thefe veins, but chiefly at the pofterior
part, between the throat and upper part of the fpine.
From the trunks of the branchial veins the blood paffcs direftly to all the other
parts of the filh, by velTels analogous to the branches of our aorta, and which
we therefore call Arteries ; and the gills and liver are the only organs which arc
not fupplied by them folcly.
T . III.
IN the Ikate the branchial veins join together, and then difperfe branches in
the following order (i).
The vein A of the uppermofl gill, which is fingle, is joined, by the canal C,
to the uppermofl: vein of the fécond gill ; and then, running inwards and upwards,
forms an artery B, which fupplies the parts of the upper jaw, the eye, the nofe,
the ear, and gives fmall branches to the fore-part of the brain.
From the uppermofl: vein D E of the fécond gill, other fmall arteries F F arc
rent off to the jaws. After that, a vein K is added, compofed of the under vein H
of the fécond gill and upper one I of the third. A little below the joining of
all tliefe veins, a rétrogradé artery L, analogous to our vertebral, is fent oif to the
brain, cerebellum, and top of the fpinal marrow, the branches of which have large
and numerous communications witli each other, and with the correfponding artery
of tlie other fide ; and from them, chiefly, the enccphalon is fupplied. Then
the trunk M, from which this artery came off, meets at N, with its fellow M,
from the other fide; and, about a finger-breadth lower, there is added, on each
fide, a vein R, formed by the under vein P of the third gill and upper vein Q_of
the fourth.
.About a quarter of an inch below tlje meeting of all the abote at T, is fent
o f f f f om cachjide, at nearly right angles, a very large artery U, analogous in
fome large branch, a, from the root of that artery
fupphes fome parts of the lower ja,^- thcn runnîng towards the fore-part of the
gills. It anaftomofes freely with the exterior ends of all ihe branchial veins (Jt),
after which it 'ends branches Q_Q,Qj;o the gills themfelvcs, which fcem to me
analogous to our bronchial arteries ; efpecially as from the fame part the heart
receives its coronary arteries (/). The reft of the great artery, which I have called
like to our fubclavian, fupplies the numerous and large mufcles and "fins on the
lide of the fifli, as far down as the fins near to the anus.
At laft, to the trunk T before-mentioned, is added a large vein X , on each fide,
which conveys the blood from the under vein S of the fourth gill, and both
veins V W of the fifth gill (m) ; and we are led by it to a great vcflil Y, which
now afliimes plainly the oflice of an artery, refembUng our aorta defcendens.
From the fore-part of this trunk two large branches cd. analogous to our caihac
and mefentcric arteries, are fent off to the chylopoietic vifcera; a fmall branch from
which enters the liver, refembhng our hepatic artery (»).
(/) Tab. I. Fig. 5. From
(.;.) Tib. I. rig. J.
(i) Vide Tab. 1. Frg. 5 . « Fig, 4. P a R R n.
(..) Scca:foTib.III.RSTUVW.
(/) Tib I. Fig, 4. S S
C I R C U L A T I O N ru F ISHES.
From the fides of the aorta the organs of generation and urine are fupplied by
fmall arteries eeee, &c. and from the lower part of the trunk are fent off two
lateral b r anche s / / that may be compared to our ihac arteries, and which fupply
the mufcles and fins at the lower part of the body.
A middle artery g runs ftraight down into the tail, covered and prote£led by
cartilage, and terminates the aortic fyflem.
From the remarkable courfe of the arteries of the heart, and of the bronchial
and hepatic arteries, fimilar to that in man, we fee clear proof, that the blood,
which, after palTing through the gills, has undergone one circulation, or rather
here has paffed through one artery and one vein, is unfit for fome office or ofiices
which are performed by the blood in the heart, gills, and liver.
Nutrition only has been mentioned by authors: but no-fully fatisfying reafon
has as yet been given, why by one circulation the blood fliould become unfit for
this purpofe; and particularly, why the gills or the lungs cannot be nouriflied,
though the whole mafs paffes through them.
T . IV.
FROM the extremities of thefe feveral arteries, the blood is returned to the
heart, by veins which in general refemble our vena portarum (0) and vens
cavas (/•).
When we examine thefe veins more accurately, we find two venK cava;, a right
and left one, equal in fize and fimilar in fituation, communicating freely by their
trunks in the abdomen, and in other places, as in the head, by their branches. In
both, the branches are much larger in their courfe than at their terminations; and
they, befidcs, form confiderable receptacles of blood. For inflance, each of the
abdominal cava has double the diameter of the cava conjoined at the heart; and
under the place at which the two cavae communicate, there is a large receptacle of
blood covered by the ovarium in the female, and by the teftes in the male (jf).
In like manner, the hepatic veins between the iiver and diaphragm form finufes
the diameter of which is ten times greater than that of their openings into the'
cavae (c).
Upon the whole, they join in the following manner. The veins from the tail
jommg with the iliac veins, form the bottom of the twd venai cava. Tab. II 24'
Then the veins from the organs of urine and generation are added, 24, ' At
26 the two abdominal cava:, which are contiguous, communicate freely'with each
other. At 27, above the diaphragm, and behind cartilages which refemble our
clavicles, the abdominal cava; join with the veins which refemble the branches of
our fupenor cava. At 28, 29, 30, veins from the mufcles of the back and latera
parts form a trunk refembling our right fubclavian vein; to which the internal
jugular 33, and external jugular 34, are foon added. A little farther in the
nght vena cava hcpatica 31, terminates; and this, at 32, is joined to the left vena
cava hcpatica. The communicating canal alfo receives the blood from a middle
W s„ T.b, „1. XX. V, zz, „ , „ , , , „^ ,„ ,, ,,, ,, ^^ j^i ^^^ ^^^