582 



OF SECRETION AND EXCRETION. 



Fig. 150. 



One of the hepatic caeca of Astacus 

 affinis (Cray fish), highly magnified, 

 showing the progress of development 

 of the secreting cells from the blind 

 extremity to the mouth of the folli- 

 cles; specimens of these, in then- suc- 

 cessive stages, are shown separately 

 at a, b, c, d, $. 



to be constructed upon a different plan ; and the 

 relation between the secreting cells of which its 

 mass is composed, and the ducts by which their 

 product is conveyed away, is very difficult to de- 

 termine satisfactorily except in certain Fishes, in 

 whose liver the ducts may be shown to terminate 

 in caeca filled with cells, as in the lower animals. 1 

 In ascending through the Yertebrated series, this 

 organ presents a more and more solid parenchy- 

 matous texture, which strikingly contrasts with its 

 loosely lobulated racemose aspect in even the highest 

 Invertebrata. This character is very obvious in 

 the liver of Man, which is peculiarly firm and com- 

 pact, 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 parts are rudimentary 

 which are elsewhere fully developed. Thus in the 

 Carnivora and Rodentia, which present the most 

 complex form of liver that we meet with among 

 Mammalia, there are five, distinct parts ; namely, 

 a " central" or principal lobe, and a right and left 

 " lateral" lobe, each with its " lobular appendage." 

 The whole mass of the liver of Man (Fig. 151), 

 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 be- 

 tween its two portions), which must be regarded as 

 the "central" lobe; the "lobulus Spigelii" is the 

 rudiment of aright " lateral" lobe, and the "lobulus 



Fig. 151. 



The inferior or concave surface of the Liver, showing its subdivisions into lobes : 1, centre of the right lobe; 

 2, centre of the left lobe ; 3, its anterior, inferior, or thin margin ; 4, its posterior, thick, or diaphragmatic 

 portion; 5, the right extremity ; 6, the left extremity ; 7, the notch in the anterior margin ; 8, the umbilical 

 or longitudinal fissure; 9, the round ligament or remains of the umbilical vein; 10, the portion of the sus- 

 pensory ligament in connection with the round ligament; 11, pons hepatis, or band of liver across the umbili- 

 cal fissure ; 12, posterior end of longitudinal fissure ; 13, 14, attachment of the obliterated ductus venosus to 

 the ascending vena cava; 15, transverse fissure ; 16, section of the hepatic duct ; 17, hepatic artery; 18, its 

 branches; 19, vena portarum; 20, its sinus, or division into right and left branches; 21, fibrous remains of the 

 ductus venosus ; 22, gall-bladder; 21, its neck ; 24, lobulus quartus ; 25, lobulus Spigelii ; 26, lobulus cauda- 

 tus; 27, inferior vena cava; 28, curvature of liver to fit the ascending colon; 29, depression to fit the right 

 kidney; 30, upper portion of its right concave surface over the renal capsule; 31, portion of liver uncovered 

 by the peritoneum ; 32, inferior edge of the coronary ligament in the liver ; 33, depression made by the verte- 

 bral column. 



1 See Dr. T. Williams, in "Guy's Hospital Reports," 1846, p. 323. 



