176 



NORMAL ANATOMY OF THE LIVER. 



A similar arrangement is seen upon the visceral 

 surface of the liver in the Llama. 



The gall-bladder is absent in all invertebrata, 

 the efferent ducts of the biliary organ termina- 

 ting for the most part by several openings in 

 the digestive stomach. In Fishes the gall- 

 bladder is observed for the first time in the 

 animal series, but it is not by any means con- 

 stant in its existence. It is absent in many 

 genera, and in these cases is frequently re- 

 placed by a dilatation upon the hepatic duct 

 and by several efferent tubes. In the class 

 Rept'dia it is invariably present, and varies 

 considerably in form, in the different genera. 

 In serpents it is placed at the extremity or 

 even beyond the liver, and occupies the space 

 formed by the pyloric contraction of the sto- 

 mach. The cystic duct is consequently ex- 

 tremely long. Among the Chelonia the gall- 

 bladder is enclosed within the substance of the 

 liver, and receives its secretion through the 

 medium of cyst-hepatic ducts. Some of these 

 ducts unite also with the cystic duct and con- 

 stitute a ductus communis choledochus. In 

 Birds the gall-bladder is occasionally absent, 

 as in Pigeons, Toucans, &c. without supplying 

 to the comparative anatomist a sufficient reason 

 for the peculiarity; being present and absent 

 in the same natural genera and under precisely 

 the same circumstances of food and climate. 

 The bile is brought from the liver by two ducts, 

 a cyst-hepatic duct which opens into the gall- 

 bladder, and an hepatic duct which terminates 

 in the duodenum near to the cystic duct. 

 When the gall-bladder is absent, both hepatic 

 ducts terminate in the duodenum. There is no 

 instance in the whole class of a ductus com- 

 munis choledochus. In Mammalia, the gall- 

 bladder is by no means constant; it is deficient 

 as a general rule, to which there are several 

 exceptions, in herbivorous animals, as in the 

 horse, stag, elephant, peccary, tapir, whilst it 

 is present in the ox, sheep, goat, antelope, &c. 

 In the first giraffe examined in this country by 

 Owen it was absent; in the next he found two. 

 Upon the hepatic duct in the elephant, near to 

 the duodenum, there is a remarkable dilata- 

 tion. In the cat and seal the ductus communis 

 choledochus is dilated in the same situation. It 

 is not uncommon to find a double gall-bladder 

 or two gall-bladders in the cat; in the kinkaju 

 this is supposed to be the normal condition ; 

 and in the Museum of the Royal College of 

 Surgeons there is a preparation, preserved by 

 Hunter, of the liver of a small animal in which 

 are three gall-bladders. 



Throughout Invertebrata the bile is secreted 

 from arterial blood. In Fishes the portal vein 

 is formed by veins returning from the tail and 

 occasionally from the air-bladder and genital 

 organs. In Reptiles a part of the blood from 

 the lower extremities unites with that from the 

 alimentary canal to constitute the portal circu- 

 lation. In Birds the portal vein also receives 

 a part of its blood from the tail and lower 

 extremities by means of its communication 

 with the pelvic veins. (Fig. 171, u, v, z, page 

 338, vol. i.) Injections of the portal vein 

 carefully conducted, as well as injections from 



the internal iliac vein, have shewn that a venous 

 communication subsists between the smaller 

 branches of the two systems in the large in- 

 testines, even in man. In support of this 

 communication Miiller, in his Physiology, 

 quotes the observations of Retzius: " Pro- 

 fessor Retzius, of Stockholm, however, has in- 

 formed me that he has discovered in man some 

 minute communications between the veins of 

 the intestines and the branches of the vena 

 cava. When he injected the vena cava and vena 

 portae with fine injection of different colours, 

 he found that the whole meso-colon and colon 

 sinistrum were injected with both colours, and 

 veins belonging to the two systems at several 

 places formed anastomoses. The veins of the 

 colon and meso-colon, which belonged to the 

 system of the vena cava and entered the left 

 renal vein, lay superficially, while those which 

 belonged to the vena portae lay for the most 

 part nearer the mucous membrane. The ex- 

 ternal surface of the duodenum also had re- 

 ceived injection from the vena cava. M. 

 Breschet too has filled the inferior mesenteric 

 vein from branches of the inferior cava, and 

 Schlemm has discovered distinct com- 

 munications of the inferior mesenteric vein 

 with branches of the inferior cava about the 

 anus." Besides these communications be- 

 tween the two systems occurring in the pelvis, 

 Kiernau points to another most important com- 

 munication upon the surface of the liver. 

 " The capsular veins," he says, " are branches 

 of the portal vein ; these vessels communicate 

 freely with branches of the phrenic veins. In 

 some cases of atrophy of the liver, and in 

 cases in which the circulation through the liver 

 has been for some time obstructed, a collateral 

 circulation is established by means of the 

 communications which take place between the 

 capsular branches of the hepatic artery and 

 portal vein and those of the phrenic artery and 

 vein." In diving animals, as in the otter and 

 seal, in which large venous reservoirs exist 

 upon the inferior cava, for collecting the re- 

 turning blood during submersion, the hepatic 

 veins are muscular. Kiernan observes with 

 regard to the hepatic veins of the seal that they 

 " differ in many respects from those of any 

 other animal I have examined. The intra- 

 lobular veins at their exit from the lobules do 

 not as in other animals terminate immediately 

 in the hepatic veins : these vessels enter the 

 hepatic venous canals, where they unite into 

 branches, which, like the vaginal branches of 

 the portal vein, are connected by a fine cellular 

 tissue, with which they form around the he- 

 patic veins a cellulo-vascular sheath precisely 

 similar to that surrounding the branches of the 

 portal vein. The structure of the two sheaths 

 is similar, but their uses are different. That 

 of Glisson's capsule has been explained ; 

 the capsule of the hepatic veins in the seal 

 appears destined to admit of the muscular con- 

 tractions of these vessels." " The external 

 coat of the hepatic veins is composed of circu- 

 lar fibres which in the larger vessels form a 

 complete tunic. In the smaller vessels the 

 fibres are arranged in the form of circular fas- 



