Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 3: Ins-Pla
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29464/1067/
PISCES. 
Salmonida, they are extremely numerous, while 
in other races, the Pleuronectidæ for example, 
there are only two coeca attached to the pylorus. 
That the pyloric appendages are strictly analo¬ 
gous to the pancreas, exhibiting that gland in 
its simplest condition, such as it presents in 
the embryonic state of the higher animals, is 
proved by the gradual transition that may be 
traced from the condition in which they exist 
as above described, and the undoubted pan¬ 
creatic gland met with in the more highly 
organized cartilaginous Fishes. Thus in the 
Cod-fish ( Gadus morrhuu) the pancreatic 
cueca unite together as they approach the duo¬ 
denum, so as to communicate with that intes¬ 
tine by comparatively few orifices situated in 
the vicinity of the pylorus ; and in the Stur¬ 
geons this coalescence of the ececal tubes is 
still more conspicuous, for in that race of 
Fishes the pyloric appendages are very short, 
and so connected together by vessels and cel¬ 
lular membrane into a single mass, that they 
here present a precisely intermediate condition 
between the free cceca of the osseous Fishes 
and the conglomerate pancreas possessed by 
the Sharks and Rays. 
In the plagiostome cartilaginous Fishes last 
named, the pancreas is in fact a true conglo¬ 
merate gland, resembling that of Quadrupeds, 
and in the same manner pouring its secretion 
into the intestine through a single excretory 
duct, which runs obliquely for a considerable 
distance between the coats of the duodenum, 
and terminates in the vicinity of the ductus 
choledochus. 
Liver.—The liver of Fishes is generally of 
very great relative size, and frequently contains 
in its tissue such an enormous quantity of oil, 
that this alone forms an important article of 
commerce. Its texture is exceedingly soft, and 
from the arrangement of the vessels in its inte¬ 
rior sometimes exhibits a fibrous appearance. 
The lobes of which it consists are generally 
very numerous, but there is always a gall-blad¬ 
der, from which the bile is poured into the 
intestines through a single duct, which termi¬ 
nates in the duodenum near the pylorus. 
Spleen.—This viscus, which is peculiar to 
the Vertebrata, first makes its appearance as 
we trace the animal series upwards in the class 
under consideration. In Fishes it is of very 
variable size, but is always present. Its usual 
position is among the folds of the intestines, 
and its relations with the stomach are so diffe¬ 
rent to what obtains in the mammiferous races, 
that its functions cannot be in any way influ¬ 
enced by pressure caused by the distension of 
that organ. In its supply of arterial blood, 
which is subsequently transmitted to the portal 
system, it differs in no essential particular from 
what occurs in the other vertebrate classes. 
All the above viscera are lodged in the cavity 
of the abdom'en, in which they are suspended 
by numerous irregular folds of peritoneum; 
the generative and urinary organs, as well as 
the swimming bladder hereafter to be described, 
being situated beneath the spine external to the 
peritoneal sac, the peritoneum only covering 
their anterior surfaces. In many Fishes the 
peritoneum does not form a closed bag, as is 
the case with the serous membranes in general, 
but on the contrary is penetrated by two large 
orifices situated in the vicinity of the anus, 
through which the peritoneal membrane be¬ 
comes continuous with the external integument, 
and in this respect assimilates a mucous sur¬ 
face. Such is the case in the Sturgeons, Lam¬ 
preys, Salmons, Sharks, and Rays : in the two 
last genera, indeed, the connection is still fur¬ 
ther extended by two orifices, through which 
the peritoneal bag communicates with the ca¬ 
vity of the pericardium. The mesentery is 
in Fishes very incomplete, consisting merely 
of irregular bands, which enclose the principal 
bloodvessels and unite the viscera to each other. 
Sometimes there are processes filled with oily 
fat representing the omentum. 
In the Branchiostoma the oesophagus com¬ 
mences at the bottom of the buccal cavity be¬ 
hind the opening of the branchial sac, between 
the latter and the spinal axis, and after a short 
course terminates in a simple dilatation, which 
forms the stomach. About the middle of the 
branchial sac the alimentary tube becomes im¬ 
bedded in the liver, and terminates in a delicate 
intestine, which extends to the anal opening. 
Lymphatic system.—The principal lacteal 
vessels are situated near the large branches 
of the cœliac and mesenteric arteries and veins, 
and the large lymphatic trunks derived from 
the spleen, liver, and pancreas, accompany the 
chief bloodvessels of those parts.* 
The lacteals and lymphatics of the assistant 
chylopoietic viscera are much larger in propor¬ 
tion to the bloodvessels than in Quadrupeds, 
Birds, or even in Reptiles. Their branches 
communicate with each other freely and repeat¬ 
edly, and instead of uniting into one or two 
trunks, they form a right and left plexus, which 
are continued undiminished in size till they are 
about to join with the lymphatic system of the 
rest of the body. Neither the lacteal nor 
lymphatic vessels are quite cylindrical, but by 
being contracted a little in many places seem 
to be jointed, so that the anatomist would ex¬ 
pect to find numerous valves in their course, 
yet these are entirely wanting, except at the 
termination of the whole system. 
The lacteals terminate in a very remarkable 
structure, which is situated along the great 
curvature of the stomach. This consists of an 
elongated viscus, the interior of which is en¬ 
tirely cellular, so that, when prepared by infla¬ 
tion and drying, its internal texture resembles 
the cancellated structure of bones, being com¬ 
posed of a great many cells of very irregular 
shapes, and all communicating with each other, 
so that probably this cellular viscus may per¬ 
form the office of the absorbent glands of other 
animals, which in Fishes are totally wanting. 
Pursuing the right and left plexuses formed by 
the lacteals and lymphatics of the chylopoietic 
organs, we are led upwards along the sides 
and back part of the oesophagus to the sides of 
the spine and of the inferior venae cavæ, and 
* Monro, Structure and Physiology of Fishes, 
fol. 1785.
        

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