THE LIVER SECRETION OF BILE. 



513 



active, it is much smaller, but is placed on the median line, in conformity with 

 the general symmetry of their internal as well as external organs ( 51). In 

 Mammalia, also, it is comparatively small ; but, though reduced in proportional 

 size, it is at the same time much more compact and firm than in the lower Ver- 

 tebrata. The Liver of Man is much less developed than that of many other 

 Mammalia ; and presents, as rudimentary indications, certain organs which 

 are elsewhere fully developed. The whole mass, which we are accustomed to 

 describe as consisting of a right and left lobe, does in reality form but one (there 

 being no real division between 



its two portions), which must [Fig. 135 



be regarded as the Central 

 lobe ; the Lobulus Spigelii is 

 the rudiment of a second or 

 light lobe, and the Lobulus 

 Caudatus is a Lobule developed 

 from it. In the Carnivori and 

 Rodentia, which present the 

 most complex form of Liver 

 that we meet with among 

 Mammalia, there are five dis- 

 tinct parts ; a central or prin- 

 cipal lobe, corresponding with 

 the principal part of. the liver 

 of Man ; a right lateral lobe, 

 with a lobular appendage, cor- 

 responding to the Lobulus 

 Spigelii and Lobulus Cauda- 

 tus ; and a similar lobe and 

 lobule on the left side. The 

 Gall-bladder is an appendage 

 to the Liver, of which we find 

 no traces in the Invertebrata. 

 It may be regarded as simply 

 a dilatation of the efferent duct, 

 more or less prolonged from it, 

 adapted to store up the hepatic 

 secretion against the time when 

 it may be required. In Fishes 

 it frequently, but by no means 

 constantly, presents itself; in 

 Reptiles, on the other hand,it 

 invariably exists. In Birds it 

 is occasionally absent, even in 

 species closely allied to others 

 that possess it, and without any 

 marked difference in the food, 

 habits, &c., of the two. In 

 Mammalia, again, it is frequent- 

 ly absent, especially among 

 herbivorous animals ; some- 

 times, on the other hand, two 

 are present, a second or ac- 

 cessary gall-bladder being formed upon the Ductus communis choledochus, 

 which elsewhere not unfrequently presents a dilatation in the same situa- 



Shows the three coats of the Gall-Bladder separated from 

 each other; 1, the external or peritoneal coat; 2, the cellular 

 coat with its vessels injected; 3, the mucous coat covered 

 with wrinkles ; 4, 4, valves formed by this coat in the neck of 

 the gall-bladder j 5, 5, orifices of the mucous follicles at this 

 point] 



[Fig. 136. 



A view of the Gall-Bladder distended with air, and with 

 its vessels injected; 1, cystic artery; 2, the branches of it 

 which supply the peritoneal coat of the liver; 3, the branch of 

 the x hepatic artery which goes to the gall-bladder; 4, the 

 lymphatics of the gall-bladder.] 



