992 
tion at the opposite side of the vascular circle. 
The branches which afterwards unite to form 
the single pulmonary artery on each side are 
given off from near the termination of the 
second and third pairs of the primitive aortic 
trunk, which thus combine the functions of 
both systemic and pulmonary arteries. The 
rons artery, formed by the union of the 
ranches from the second and third branchial 
arteries, descends between the vena cava (fig. 
525, e) in front, and the left branch of the 
vena pulmonalis (f') behind to the interspace 
to the lungs; here it distributes branches to the 
anterior lobes, and then divides; each division 
extends along the mesial side of its correspond- 
ing lung to the extremity. The blood distri- 
buted by the capillaries of this artery over the 
cells of the lung is collected into a vein (7) 
which returns along the lateral or outer margin 
of the lung as far as the commencement of the 
lobulated part; here it crosses obliquely the 
anterior surface of the lung and unites with its 
fellow. The common pulmonary vein runs 
parallel with and behind the vena cava for a 
few lines, then obliquely pierces the pericar- 
dium, and enters the sinus formed by the ex- 
pansion of the vena cava, and continues attached 
to the parietes of that sinus till it reaches the 
auriculo-ventricular aperture, where it termi- 
nates close behind the cartilaginous knob 
before mentioned.* 
Portal system of veins—All the blood de- 
rived from the stomach, from the intestines, 
and from the spleen, is collected into one or 
sometimes into several trunks, which convey it 
into the liver for the elaboration of bile pre- 
' cisely as in other races of Vertebrata. In some 
genera, however, more especially the Cypri- 
nide, the lobes of the liver are so intervolved 
with the intestinal folds, that the venous blood 
from the intestines enters the liver through 
innumerable small branches, none of which 
are of sufficient size to be regarded as a main 
trunk of the portal vein. Rathke,ft indeed, 
observes, in relation to this subject, that 
the vena porte of Fishes exhibits a kind of tran- 
sition in its arrangement, a sort of tendency to 
perfection indicated by progressive concentra- 
tion of the venous trunks according to the fol- 
lowing ‘scale:—As an improvement upon the 
portal system of the Ciprinide, in Cottus scor- 
pio all the veins bringing the blood from the 
abdominal viscera form three aie trunks, 
which enter the liver separately. In Cobitis 
Jossilis most of these veins are found united 
into two trunks, which penetrate the liver sepa- 
rately; but besides these there are some strag- 
gling branches which keep themselves inde- 
ndent of the two great veins. In the Blenny 
and the Pike there are only two portal trunks. 
In the Lump-fish, the Shad, c., the two 
trunks are united into one; but there are still 
small veins which run isolatedly into the sub- 
stance of the liver; and lastly, in the Eel, the 
Perch, &c., there is only one vena porte, as in 
the most highly organized vertebrate animals, 
* See Professor Owen’s paper, ubi supra. 
+ Annales des Sciences Nat, tom. ix. p. 170. 
PISCES. 
There is a remarkable circumstance connected 
with the great venous trunk above alluded to 
which accompanies the spinal cord lodged in 
the superior vertebral canal, for this vein, al- 
though it receives a good proportion of the 
blood derived from the muscles of the upper 
part of the trunk, does not empty itself into the 
venous sinus of the heart, and, from the cireum- 
stance of its giving off numerous large branches 
to the substance of the kidney, has been re- 
garded as forming a renal portal system, similar 
to that described by Jacobson as existing in 
Birds. It must, however, be observed that this 
superior vein communicates very freely with the 
inferior vein, which indubitably represents the — 
vena cava inferior, and consequently the renal 
branches may be derived from, and not distri- 
buted to, the kidney. fed 
Lateral system of vessels—Dr. Marshall 
Hall discovered some years ago a peleing, 
cavity or heart situated near the caudal extre- — 
mity of the vertebral column of the Eel, the con- 
tractions of which were found to be quite inde- 
pendent of the pulsations of the branchial heart, 
this organ beating 160 times in a minute, while — 
the pulses of the branchial heart were only 60. 
This structure, the existence of which only was 
pointed out by Dr. Marshall Hall, has since 
been carefully investigated by M. Hyrtl,* 
and the following is the result of that gentle- 
man’s explorations. The organ in question is 
easily seen by stretching out the tail of an Eel 
upon a piece of glass, to which it readily ad- 
heres owing to the viscid secretion furnished by 
the skin. Its pulsations are very lively, and it 
seems surrounded by a transparent areola, which — 
eee to M. Hyrtl to consist of two 
e disorganization of, the spinal marrow by 
means of a wire had no effect upon the number 
of its pulsations, and even when the branchial 
heart was tied or the animal cut in two, the 
caudal heart continued to beat for five or six 
minutes. The genera in which the caudal 
heart and the apparatus connected with it 
were examined, were Accipenser, Salmo, P. 
Abramis Leuciscus, Gadus, Gobio, Silurus 
Esox, Cyprinus, Zeus, Lophius, and sever 
others, so that doubtless the system unde 
consideration is common to the whole class 
Fishes. ; 
Brain.—The encephalon of Fishes is remark 
able for its diminutive size in proportion to th 
dimensions of the animal, and also with rela 
tion to the nerves which are derived from it 
in fact it occupies but a very small portion ¢ 
the cavity of the cranium, the wide interval exi: 
ing between its surface and the dura mater th 
lines the cranial parietes being filled up w 
loose cellulosity filled with fluid, and sor 
times containing abundance of oil, or in certa 
instances, as for example in the Sturgeon ar 
Tunny, of a compact and fatty substance. — 
It has been remarked that this interval 
tween the cranium and the surface of the br 
is much less in young subjects than in adults. 
acs. 
* Archiv. fiir Anat. Phys. und Wissenscha 
eat herausgegeben von J, Muller. 
