NORMAL ANATOMY OF THE LIVER. 



177 



ciculi, which are connected with each other 

 by oblique intermediate fibres. All the fas- 

 ciculi do not extend completely round the 

 veins ; some, dividing into two portions, unite 

 with fibres from those above and below, and 

 form other fasciculi." " In the porpoise the 

 hepatic veins are connected to their canals ; 

 no circular fibres are seen in their coats. Their 

 external surface is reticulated, the ridges cor- 

 responding to the interlobular fissures, where 

 the interlobular cellular tissue is continuous 

 with the cellular coat of the veins. The mouth 

 of an intra-lobular vein occupies the centre of 

 each space circumscribed by the ridges." 



The distribution of the vessels in the liver 

 in the three great classes, Reptilia, Aves, and 

 Mammalia, has been ascertained to be the same 

 with that which has been so completely illus- 

 trated in the discoveries of Kiernan. In 

 Fishes but few observations have been made, 

 but analogy would lead us to infer that the ge- 

 neral arrangement must be the same. 



Development of the liver in the embryo. 

 The development of the liver in the embryo 

 commences so early in Mammiferous animals, 

 hurries so rapidly through its different phases, 

 and is completed so soon, that it has hitherto 

 been impossible to obtain any connected and 

 precise information with regard to its progress. 

 The observations of eminent physiologists made 

 from time to time have, however, shewn that 

 the mode of its development is in all respects 

 similar to the development of the liver in the 

 chick. Indeed, the egg of the bird is in the 

 highest degree favourable to anatomical exa- 

 mination, both on account of its large size and 

 the facility with which the incubated egg may 

 be obtained from hour to hour, and from day 

 to day. The principle of development there- 

 fore being the same in the ovum of the bird as 

 in Mammifera, I shall here trace the progress 

 of the liver in the chick according to the most 

 recent researches of Baer. 



In the embryo of the fowl at the commence- 

 ment of the third day, the common vein of the 

 body is embraced by two pyramidal ccecal 

 pouches which communicate by their bases 

 with the intestinal canal, and which shoot for- 

 wards so as to carry before them a fold of the 

 vascular layer of the germinal membrane, in 

 which they begin to ramify by giving off ccecal 

 branches from their sides and extremities. 

 These two coecal tubuli with their correspond- 

 ing ramifications form two flattened processes, 

 which represent the two lateral lobes of the 

 liver. By the end of the third^day the two 

 processes resemble folds of the vascular layer 

 in which the tubuli are seen ramifying; they 

 have increased in size and almost surround the 

 vein. On the fourth day the liver has the appear- 

 ance of two flattened processes which enclose 

 the vena portse. The hepatic tubuli have be- 

 come lengthened and further removed from the 

 intestine, and have ramified more freely in the 

 vascular layer. By their bases the hepatic 

 tubuli approach nearer to each other, and at 

 the end of the fourth day they coalesce and 

 form a common tube. On the fifth day the 

 liver has attained considerable size ; its two 



VOL. Ill, 



lobes have become thick and appear to possess 

 a spongy texture in their interior. The hepatic 

 ducts are connected with the intestine by a 

 common duct, the ductus communis chole- 

 dochus ; and the portal vein gives off large 

 branches which are distributed among the ra- 

 mifications of the ducts. On the sixth and 

 seventh days the liver receives an abundance 

 of blood and is nearly as red as the auricle of 

 the heart. The left lobe is sensibly smaller 

 than the right. On the eighth, ninth, and 

 tenth days the liver has lost its great redness 

 and presents a yellowish brown tint; the vessels 

 have diminished in calibre, while the paren- 

 chyma has increased, and the gall-bladder has 

 become apparent. The succeeding days aug- 

 ment the size of the organ, and mould it to 

 the form which it possesses after the escape of 

 the chick from the egg ; it begins to secrete 

 bile; and the gall-bladder assumes the pyri- 

 form shape which it retains in after-life. 



In the human ovum the formation of the 

 embryo commences visibly at about the third 

 week of intra-uterine existence; the parietes 

 which separate the embryo from the ovum begin 

 to be developed, and rudiments of the intestinal 

 canal, the liver, and the heart soon become 

 distinctly visible. Upon its earliest appearance 

 the liver is of large size, and between the third 

 and the fifth week is one-half the weight of 

 the entire body, divided into several lobes of 

 a reddish grey colour, and receives a large pro- 

 portion of blood from the omphalo-mesenteric 

 vein. From the fifth to the eighth week the 

 liver extends as low as the margin of the 

 pelvis; it is soft, almost pulpy, and greyish in 

 colour. The gall-bladder is developed in the 

 form of a lengthened filiform cord, having an 

 extremely minute canal through its centre. By 

 the third lunar month the liver extends nearly 

 to the pelvis and almost fills the abdomen, and 

 the right lobe has increased somewhat beyond 

 the left. The texture is more firm and of a 

 redder colour, and the gall-bladder is long and 

 conical. At the fourth lunar month the liver 

 is still prolonged nearly to the margin of the 

 pelvis, but the left lobe is evidently shorter 

 than the right. The gall-bladder is elongated, 

 straight, and vertical in direction, and contains 

 a little mucus. Upon its internal surface a 

 few rugae begin to be perceived ; it receives no 

 bile, although a small quantity of that fluid is 

 secreted by the liver and poured into the in- 

 testine. By the fifth lunar month the liver has 

 acquired an increased consistence and deeper 

 colour. It no longer descends so low as the 

 pelvis, but appears to have diminished in bulk 

 in proportion with the size of the abdomen. 

 The gall-bladder assumes a more horizontal 

 direction, and the contained mucus has a yel- 

 lowish green tint. The openings of the ductus 

 choledochus and pancreatic duct, at first placed 

 at a considerable distance from each other, 

 approximate and produce less projection of 

 the mucous membrane. By the sixth lunar 

 month the descent of the liver is still more 

 curtailed, the foetus increases in development 

 from before backwards, and the organ becomes 

 more horizontal. By the seventh lunar month 



