174 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



Into two parts, and this vein is retained in a rudi- 

 mentary condition in the adult as the round liga- 

 ment. It may, therefore, be taken as lying in the 

 middle line of the liver ; the parts or lobes that lie on 

 one side are the right lobes, those that lie on the 

 other are the left lobes. The fissure in which the 

 remains of the umbilical vein lie is called the 

 umbilical fissure, but it is not always the deepest ; 

 where a lateral fissure is as deep, or deeper, the 

 liver appears to lose its bilobate character, and seems 

 often to consist of three chief parts. The characters 

 and relations of the umbilical fissure must, therefore, 

 be carefully borne in mind if we desire to retain the 

 proper morphological conception of the liver as an 

 originally bilobed organ. A well-marked lateral 

 fissure being frequently found on either side of the 

 umbilical, it results that the organ is often found to 

 consist of four chief lobes ; these, from their topo- 

 graphical relations, may be spoken of as right 

 central, left central, right lateral, and left 

 lateral ; while the whole mass of lobes on either 

 side of the primitive middle line may be called re- 

 spectively the right and left segments. 



So far, then, we find that the liver is an organ 

 consisting of two segments, each of which may be 

 divided into two or more lobes. All the more impor- 

 tant modifications of the liver affect its right segment; 

 with the right central there is very frequently con- 

 nected a reservoir or gall bladder ; the right lateral 

 often develops a prolongation on its lower surface, 

 which is known as the spigelian lobe ; another 

 accessory to be developed from the right lateral is the 

 so-called caudate lobe. 



While all these parts are to be found in the human 

 liver, we find some considerable variations exhibited 

 in different mammalia ; in some cases (Cetacea, Peris- 

 sodactyla, and some other Ungulata, etc.) the gall 



