470 



OF SECRETION AND EXCRETION. 



FIG. 165. 



wards the outlet, it becomes evident that the cells originate in the former 



situation, arid gradually increase in size as they ad- 

 vance towards the latter. It is also to be observed 

 that the cells which lie deepest in the ctecum (a, 

 6), contain for the most part the yellow granular 

 matter, which may be regarded as the proper bil- 

 iary secretion ; but as they increase in size, there 

 is also an increase in the quantity of oil-globules 

 which they contain (c), until past the middle of 

 the follicle, where they are found full of oil, so as 

 to have the appearance of ordinary fat-cells (d, e). 

 From this it happens, that when an entire crecum is 

 examined microscopically, its lower half appears 

 filled with a finely-granular matter, intermingled 

 with nucleated particles ; and the upper half with a 

 mass of fat-cells, whose nuclei are obscured by the 

 oily particles. 1 In vertebrated animals, the Liver 

 seems to be constructed upon a similar plan. Its 

 component cells, which have not been proved to 

 possess a definite cell-wall, are still contained in 

 distinct ceecal follicles or elongated tubuli branch- 

 ing off from the excretory ducts ; but in ascending 

 through the Vertebrated series, it presents a more 

 and more solid parenchymatous texture, which 

 strikingly contrasts with its loosely-lobulated race- 

 mose aspect in even the highest Invertebrata. 

 This character is very obvious in the liver of Man, 

 which is peculiarity firm and compact, and has less 

 of connective tissue between its different parts than 

 is found in that of many other Mammalia. It is 

 observable, moreover, in the Human liver, that 

 certain portions are rudimentary, which are else- 

 where fully developed. The liver in Mammalia, as 

 in the lower vertebrates, is essentially a bilobed organ, but this character is 

 usually more or less concealed by the various accessory fissures by which it is 

 divided into many lobes ; always, however, on the same general plan. The 

 fissure in which the umbilical vein runs constitutes the primary division into 

 right and left segments. In the most complex forms usually met with in the 

 Quadrumana, Carnivora, Insectivora, llodentia, Edentata, Marsupialia, etc., 

 the left segment is further divided by the left lateral fissure into a left lateral 

 and a left central lobe. The right segment is similarly divided into a rigid 

 central and right lateral lobe; and it has moreover two accessory lobes on its 

 under surface, the Spigelian and the caudate. When the gall-bladder is 

 present it is attached to the under surface of the right central lobe. In most 

 Ungulates, in Cetacea, in the highest Apes, and in Man, the lateral fissures 

 are not present, and the liver appears of simpler form. In Man the sim- 

 plicity is further increased by the caudate being hardly distinguishable from 

 the right lateral lobe and the Spigelian lobe being but little developed. J 



1 Leidy, Amer. Journ. of Med. Sci., Jan. 1848. 



2 See W. H. Flower, On the Organs of Digestion of Mammalia, Mod. Times and 

 Gazette, March 9th, 1872, et srq. The weight of the Liver is from 48-58 oz in the 

 male, and from 40-50 oz. in the female. Its sp. gr. is about 1.05 From the exam- 

 ination of a large number of bodies, Steffan (Jahrlmeh f. Kinderheilk., N. F., Bel. v, 

 p. 47) found that the ratio of the weight of the Liver to the body weight is greatest 

 after birth, and that it diminishes during the first year, especially in boys. In child- 

 hood the l>u<ly weight and the liver weight increase, but not in equal proportion, the 

 former augmenting fastest. 



One of the Hepatic cieca 

 of Astacus affinis (Crayfish), 

 highly magnified, showing the 

 progress of development of the 

 secreting cells from the blind 

 extremity to the mouth of the 

 follicles; specimens of these, 

 in their successive stages, are 

 shown separately at a, b, c, d, e. 



