ON THE LIVED, SPLEEN, AND OMEN TUN. • The spleen and omentum seem to be less constantly found in the animal kingdom than the liver, and to be in a manner subservient to the latter viscus ; which, on the contrary, exists in every class and order of animals that is pro vided with a heart and circulating sys tem.
It deserves to be remarked here, as a peculiarity of the liver of some four footed mammalia, which live in or about the sea, namely, the polar bear and some seals, that it seems to possess some poi sonous or noxious qualities when employ ed for food. lleemskerk's companions experienced this, in the former instance, at Nova Zemlia ; and Lord Anson's squad ron, in the latter, on the coast of Pata gonia.
The liver of mammalia is in general di vided into more numerous lobes ; and the divisions are carried deeper into its sub stance than in the human subject. This is particularly the case in the carnivora, where the divisions of the lobes extend through the whole mass. But the utility, which Munro has assigned to this struc ture, viz. that of its allowing the parts to yield and glide on each other in the rapid motions of the animal, carries very little plausibility with it. " Essay on Compara tive Anatomy," p. 11.
In many animals of this class, as the horse, the ruminantia, the pachydermata, and whales, the liver is not more divided than in man.
The ductus coledochus forms a pouch between the coats of the intestine, for re ceiving the pancreatic duct, in the cat and elephant.
All the quadrumana, carnivora, and edentata, have a gall-bladder.
Many rodentia, particularly among the rats, want it. The tardigrada ; the ele phant, rhinoceros, and pecari, among the pachydermata ; the genus cervus and ca melus, among the ruminating animals ; the solipeda ; the trichechus and porpoise also want this part. It does not exist in the ostrich and parrot ; but is found in all the reptiles. Cuvier thinks that it be longs particularly to carnivorous animals ; that it is connected with their habit of long fasting ; and serves as a reservoir for the bile.
All the mammalia which want it, ex cept the porpoise, are vegetable eaters: and most reptiles, which universally pos sess it, live on animal food.
The liver of birds is divided into two equal lobes. The hepatic duct opens ser parately from the cystic ; and its termina tion is generally, but not always, preced ed by one or more pancreatic ducts, an3 followed by that of the cystic duct.
The fundus of the gall-bladder receives branches from the hepatic duct (" ductus hepaticystici") ; but the tube sometimes unites with the cystic, as in the duck.
Some fishes, which are most destitute of fat in the rest of their body, have an abundance of oil in their liver, as, for in stance, the skate and cod.
The spleen gradually diminishes in size from the mammalia to fishes. In the por poise there are several small spleens, sup plied from the arteries of the first sto mach. It is always attached to the first, when there are several stomachs.
In birds it is always near the bulbus glandulosut, but does not lie constantly very close to the stomach in reptiles, as it is found in the mesentery of the frog ; neither is it very uniformly situated in fishes.
In the crustacea the liver is large, and consists of blind tubes, opening into the commencement of the intestine. It forms the soft high flavoured substance of the crab and lobster.
A liver exists in all the mollusca, and is very large ; but this class has no gall bladder. The liver is supplied with blood from the aorta, and there is conse quently no vena portarum.
It is a completely mistaken notion, that the black fluid of the cuttle-fish is its bile. The ink-bag is indeed found between the two lobes of the liver in the sepia octo pus; and in front of them in the calmar ; but in the common cuttle-fish (" sepia officinalis"), it is at a considerable dis tance from this organ.
The real bile is poured, as usual, into the alimentary canal.
The structure of the pancreas in the mammalia, in birds, and in reptiles, is the same, on the whole, as in the human subject ; its form and size, its colour and consistence, and its division into lobules, exhibit some slight and unimportant vari ations.
The termination of its duct or ducts is distinct in birds from that of the D. cho ledochus. In the mammalia they generally open together, or there is a branch termi nating in the D. choledochus, and another opening into the intestine, as in the dog and elephant ; or they may be quite dis tinct, as in the hare, porcupine, and mar mot. They may be separate or distinct in different individuals of the same species, as in the monkeys.
The skate and shark have a pancreas similar to that of the three first classes of red-blooded animals. In other fishes the situation of this organ is occupied by nu merous small tubes, called the czcal ap pendices, or pyloric caeca ; which afford a copious secretion, analogous, no doubt, to the pancreatic liquor. The internal sur face of these tubes becomes very red on injection, and possesses a glandular and secreting appearance. Their number va ries from one to several hundreds.
The description of the organs which are concerned in assimilating the food, and in converting it into chyle, will be naturally followed by that of the blood vessels, which carry it to all parts of the body ; of the organs of respiration, which subject it to certain important changes , and of the absorbent system.