624 



OF SECRETION. 



Fig. 232. 



Glandular cells of 

 Liver; a, nucleus ; b, 

 nucleolus (?); c, adi- 

 pose particles. 



Fig. 233. 



close relation to the latter than to the former. Their diameter 

 is usually from l-l500th to l-2000th of an inch; and they are conse- 

 quently easily recognized, whenever a portion of the substance of 

 the Liver is torn up and examined with the higher powers of the 

 Microscope. Their shape is usually spheroidal. They have a distinct 

 biliary tinge ; and contain a granular amorphous matter, with a few 

 small adipose globules. 



g. In regard to the Embryonic Development of the Human Liver, 

 a considerable part of our information must necessarily be derived 

 from the study of that of other animals ; and this not so much from 

 Mammalia, as from Birds ; since the development of this organ com- 

 mences so early in the former, its phases are so rapidly hurried 

 through, and its evolution is so soon completed, that the process cannot 

 be continuously watched. In the Chick, the rudiments of the Liver are found at the commence- 

 ment of the third day of incubation, in the 

 form of two crecal pouches, which are pro- 

 longed from the Intestinal tube ; these carry 

 before them a fold of the vascular layer, from 

 which the blood-vessels subsequently origin- 

 ate ; and they soon begin to ramify in this, 

 sending oft" branches, of which the coecal ex- 

 tremities are still evident. At the end of the 

 fourth day, the tubuli and their ramifications 

 have attained a considerable size ; arid they 

 approach each other and coalesce at the base, 

 entering the intestine by an orifice common 

 to the two. In this process, it is easy to re- 

 cognize the analogy to the succession of 

 forms, which we encounter in ascending the 

 animal scale. The size and density of the 

 organ are gradually increased; but it is not 

 until several days afterwards, that the gall- 

 bladder is developed. In the Human Em- 

 bryo, the formation of the Liver begins at 



Origin of the Liver from the intestinal wall, in 

 the embryo of the Fowl, on the fourth day of incu- 

 bation ;- a, heart ; 6, intestines ; c, everted portion 

 giving origin to the liver; d, livery e, portion of 

 yolk-bag. 



about the third week of intra-uterine existence ; the organ is from the first of very large 

 size, when compared with that of the body; and between the third and the fifth week, it is 

 one-half the weight of the entire embryo. It is at that period divided into several lobes. 

 By the third lunar month, the liver extends nearly to the pelvis, and almost fills the abdo- 

 men ; the right side now begins to gain upon the left ; the gall-bladder begins to appear at 

 this time. The subsequent changes chiefly consist in the consolidation of the viscus, and the 

 diminution of its proportional size. Up to the period of birth, however, the bulk of the 

 Liver, relatively to that of the entire body, is much greater than in the adult; the proportion 

 being as 1 to 18 or 20 in the new-born child, whilst it is about 1 to 36 in the adult: and 

 the difference between the right and left sides is still inconsiderable. During the first year of 

 extra-uterine life, however, a great change takes place; the right lobe increases a little or re- 

 mains stationary, whilst the left lobe undergoes an absolute diminution, being reduced nearly 

 one-half; and as, during the same period, the bulk of the rest of the body has been rapidly 

 increasing, the proportion is much more reduced during that period, than in any subsequent 

 one of the same length. According to Meckel, the liver of the newly-torn infant weighs 

 one-fourth heavier than that of a child of eight or ten months old ; and as the weight of the 

 whole body is more than doubled, during the same time, it is obvious that the change in the 

 proportion of the two must be principally effected at this epoch. 



827. The knowledge of the distribution of the Biliary ducts, and of the two 

 chief systems of Blood-vessels, in the Lobules of the Liver, has enabled Mr. 

 Kiernan to give a most satisfactory explanation of appearances, by which 

 Pathological anatomists had been previously much perplexed. When the 

 Liver is in a state of Anaemia (which rarely happens as a natural condition, 

 although it may be induced by bleeding an animal to death), the whole sub- 

 stance of the lobules is pale, as represented in Fig. 234. In general, how- 

 ever, the Liver is more or less congested at the moment of death; and this 

 congestion may manifest itself in several ways. The whole substance may 

 be congested; in which case the lobules present a nearly uniform dark colour 

 throughout their substance, their centres being usually more deeply-coloured 



