THE LIVER SECRETION OF BILE. 517 



designated those lobules which lie upon the exterior of the glandular substance, not only 

 upon the surface cf the Liver, but also against the walls of the larger vessels,ducts,&c.,) 

 the Intralobular Veins commence directly from their surface; and the minute venules of 

 which each is composed may be seen in an ordinary injection, converging from the 

 circumference towards the centre, as in the transverse section of other lobules* The 

 Intralobular Veins terminate in the larger trunks, which pass along the bases of the 

 lobules, collecting from them their venous blood; these are called by Mr. Kiernan sub- 

 lobular veins. The main trunk of the Hepatic Vein terminates in the ascending Vena 

 Cava. 



/. In regard to the mode in which the nucleated Cells, that are the real agents in the 

 Secreting process, are arranged in the Liver of Man and the higher animals, there is 

 much uncertainty; owing especially to our want of acquaintance with the mode in which 

 the Hepatic Ducts terminate. They would seem to form the greatest part of the paren- 

 chyma, which fills up the interstices between the reticulations of the Blood-vessels and 

 Ducts ; but it is obvious, from their functional operation, that they must have a more 

 close relation to the latter than to the former. Their diameter is usually from l-15UOth to 

 l-2000th of an inch; and they are consequently easily recognized, whenever a portion of 

 the substance of the Liver is torn up and examined with the higher powers of the Micro- 

 scope. Their shape is usually spheroidal. They have a distinct biliary tinge ; and 

 contain a granular amorphous matter, with a few small adipose globules. (Fig. 139.) 



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 commences 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 commencement of the third day of 

 incubation, in the form of two coscal pouches, which are prolonged from the Intestinal 

 tube; these carry before them a fold of the vascular layer, from which the blood-vessels 

 subsequently originate; and they soon begin to ramify in this, sending off branches, of 

 which the coscal extremities are still evident. At the end of the fourth day, the tubuli 

 and their ramifications have attained a considerable size; and 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 recognize the analogy to the succession of forms which we en- 

 counter 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 Embryo, the formation of the Liver begins at 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 abdomen ; 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 pro- 

 portion 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 remains stationary, whilst the left lobe undergoes an absolute dimi- 

 nution, 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-born 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 doubted, during the 

 same time, it is obvious that the change in the proportion of the two must be principally 

 effected at this epoch. 



656. 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. 142. In general, however, 

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

 44 



